Dynamic photochromism in cocrystals and tri-state fluorescence switching in films for multilevel optical encryption

Domain: neuroscience
Published: 2026-02-10
Editorial outcome: minor_revision

Abstract
Organiccrystallinesystemscombiningdynamicphotosalienteffectwithstatic
photochromismrepresentapromisingclassofintelligentresponsivemateri-
als.Inthiswork,weconstructa3Abf-Ofncocrystal(3Abf=3-aminodibenzo-
furan,Ofn=Octafluoronaphthalene)throughmolecularco-assemblystrategy.
UponUVirradiation,the3Abf-Ofnundergoesasolid-statetransformation
involvingvolatileOfnreleaseandN-Ncouplingof3Abftobis(benzofuran-3-yl)
azocompound(Bfa),triggeringsignificantphotochromismandphotosalient
behavior.Thisreactionpathwaydiffersfromconventionalmechanismssuch
asphotoisomerizationorcycloaddition,representinganexampleofsuch
photochemicalprocessinorganiccocrystals.Furthermore,the3Abf-
Ofn@PMMAcompositefilmexhibitsdynamicallytunablefluorescenceunder
UVirradiation:aninitialenhancementoffluorescenceuponphotoactivation,
followedbyexcitationwavelength-dependentemission(EWDE)andpro-
gressivefluorescencequenching,showinggreatpotentialforadvancedanti-
counterfeitingandinformationencryptionapplications.Thisworknotonly
providesvaluableinsightsfordesigningmultifunctional,light-controlled
organicluminescentmaterialsbutalsoofferscomplementarysynthetic
approachestoazo-aromaticcompounds.

Introduction
Photo-responsive dynamic materials, capable of exhibiting various common dynamic photomechanical molecular crystalline materials
macroscopicmechanicaleffects(suchasbending,twisting,rotating, havemainlybeeninvestigatedinlight-sensitivechromophoresystems
jumping,expanding,andfragmentation)inresponsetolightstimuli, (e.g.,diarylethenes,azobenzenes,anthracenes,andstilbenes)12–16.The
have received widespread attention in the fields of soft robotics, mechanical motions of such molecular crystals are predominantly
flexibleelectronics,sensors,andactuators1–5.Inparticular,lightasa driven by photochemical reactions, including photoisomerization,
non-contactstimulussourcepossessesinherentadvantagesofclean- photocycloaddition, photodimerization, and other photoinduced
liness,adjustabilityinrealtime,andhighprecision,presentingapro- reactions, thereby releasing accumulated strain energy. Once the
mising opportunity for the further development of intelligent strain is above the threshold and isn’t canceled, the macroscopic
photomechanical materials. In addition, compared with polymer- photo-responsive mechanical motions would be observed17–20. Cur-
based materials such as hydrogels, rubbers, and liquid crystals6–8, rently, many photo-responsive crystalline materialscan dynamically
molecularcrystalsstandoutfortheirfastresponse,aswellasrapid respond to light stimuli. However, research on integrating multiple
couplingbetweenlightandmechanicalenergywithinthelong-range distinguishable output signals for a single material is still relatively
orderedstackingstructures,whichcanbeconducivetofurthereluci- limited14.
ating the relationship between structure and photomechanical In the context of photo-responsive materials, photochromism
properties through single crystal X-ray diffraction9–11. To date, referstoaphenomenonwhereinphotosensitivesubstancesundergo
reversiblechangesincoloruponexposuretospecificwavelengthsof functionalproperties,holdssignificantscientificimportance.Particu-
light, driven by structural transformations or electronic transitions, larly,thesynergisticmechanismbetweenguestreleaseincocrystaland
whicharedistinguishedbypronouncedcolorcontrastandundetect- photochemical reactions, and how the cascade process transforms
ablefluorescentsignalsundernaturallight21–25.Thesematerialspos- molecular-scale structural evolution into dual optical-mechanical
sess advantages for high-security, diversified, and intelligent responses,haslackedsystematicinvestigation.
information protection, making them as ideal candidates for light- Inthiswork,wepresentasingleorganicmolecularcocrystalthat
inducedstaticresponseapplications26–31.Despitesignificantresearch integratesphotosensitivemechanicaleffectandphotochromism,co-
progress and widespread practical applications of organic photo- assembledfromthe3AbfandOfnbuildingblocksviadominantπ-π
chromicmaterials,theintegrationofthephotochromicprocesswith stackinginteractions(Fig.1).The3Abfmoleculeasanelectrondonor
dynamicmechanicalresponsesinasinglesystemremainsakeychal- (D)adoptsadisorderedstackingarrangement,whileOfn,asanelec-
lenge, possibly attributed to the rational design of multi-channel tronacceptor(A)satisfiesenergymatchinginthe3Abf-Ofncocrystal
responsemodesbasedonsynergisticactionmechanisms.
system. Under UV irradiation, photoinduced electron transfer (PET)
Cocrystalsengineeringenablesprecisemodulationofmolecular between 3Abf and Ofn generates cationic radicals, enabling the
conformations,intermolecularinteractions,andstructuraldimensions observationofclearphotochromicproperties.Concurrently,photo-
throughrationalselectionofco-assembledunit(co-former),achieving active3Abfundergoesaphotochemicalreactionthatrapidlypromotes
well-ordered molecular arrangement and spatial stacking at the Ofnrelease,triggeringmacroscopicmechanicalmotionsbyreleasing
supramolecularscale,oftengivingrisetoemergentphysicochemical accumulated strain. Single-crystal X-ray data (SCXRD) confirms that
properties that go beyond the simple sum of the individual Bfa isthe finalphotoproduct, rather thanundergoing complex and
components32–36.Forexample,MichaelR.Wasielewskietal.studiedthe cumbersomechemicalsynthesistraditionallyrequiredforazobenzene
influenceofchiralelectronacceptorsonchargetransferdynamicsand derivatives. Control experiments with structurally related amine
triplet exciton formation in charge transfer cocrystals37. Tang et al. donors demonstrate the potential generality of this photochemical
reportedtriethylaminevaporinducesacyclizationreactioninAOTC N–N coupling strategy. Moreover, the significant photo-induced
cocrystals,accompaniedbyacocrystal-to-polycrystalphasetransition fluorescence enhancement effect can be achieved by embedding
process,convertingthenon-emissivefluorescencestateofAOTCinto 3Abf-OfnintoPMMAmatrix.Subsequently,thefluorescencegradually
ared-emissiveACTCcocrystalandablue-emissiveAIC38.Thestructural diminishes, accompanied by progressive photochromic transforma-
tunabilityofcocrystalsmaterials39–41makethemanidealplatformfor tion upon continuous 365nm UV irradiation. The 3Abf-Ofn@PMMA
exploringlight-drivenchemicalreactions,astheirorderedmolecular filmsalsopresenttunableexcitationwavelength-dependentemission
packingcanregulatethereactivity,selectivity,andkineticbehaviorof fluorescencerangingfrombluetoredlight.Thus,thisstudyprovides
photochemical processes effectively. The convergence of crystal an advanced strategy for constructing multifunctional responsive
engineeringandphotochemistryisemergingasapromisingpathway organiccrystallinematerials,layingthefoundationfortheirpotential
for developing intelligent photoresponsive materials. Nevertheless, applicationsinopticalanti-counterfeiting.

Results
Synthesisandphoto-responsivepropertiesof3Abf-Ofn
cocrystal
3Abf-Ofncocrystalswereobtainedin1:1stoichiometryratiobyslow
evaporationfromthemixedsolvent(methanol:dichloromethane=1:1)
atroomtemperature.Thecrystallineproductspresentatransparent,
well-defined two-dimensional (2D) plate-like morphology with blue reveals the formation of 3Abf–Ofn cocrystal containing both char-
fluorescence, which are consistent with the predicted crystal mor- acteristicvibrationalpeakofbuildingblocks(SupplementaryFig.4).
phologybyBravais−FriedelDonnay−Harkercalculations22,43(Fig.2a). Thermogravimetric analysis (TGA) shows the 3Abf-Ofn cocrystal
Thepredictedmorphologyshowsthatthelargestcrystalfacescorre- exhibits good thermal stability and remain undecomposed until
spondtothe(002)millerplanebasedonthesingle-crystalstructure reaching145.8°C(SupplementaryFig.5),whichdiffersfromthermal
analysis, which is parallel to the slipped 3Abf–Ofn columnar stacks behaviorthatoftheindividual3AbfandOfnmolecules(Supplemen-
(Fig. 2b). The crystallographic data of 3Abf-Ofn cocrystal (Supple- taryFig.6),furtherconfirmingtwo-componentself-assemblystrategy
mentary Table 1) show it belongs to a monoclinic system with the can effectively modulate the thermal stability of single-component
centrosymmetricspacegroupofP2/c(No.14).Adjacent3Abfmole- systems.
1
culesadoptahead-to-tailstackingmodewithcloseoverlapanddis- As shown in Fig. 3a and Supplementary Movie 1, the obvious
orderedconformations,whichmayfacilitatethesusceptibilityofthe staticphotochromicbehavioranddynamicphotomechanicaleffect
materialtointernalstrain.Thedisorderofthe3Abfmoleculearises of macroscopic 3Abf-Ofn crystals can be first observed simulta-
fromitscrystallographicplacementataspecialposition,asthelocal neously,whichareabsentinthe3Abfcrystals(SupplementaryFig.7).
symmetryofthelatticesiteishigherthantheintrinsicsymmetryofthe UponirradiationwithUVlight(365nm,441mW/cm2),the3Abf-Ofn
3Abf molecule, which crystallizes in the orthorhombic Pna2₁ space crystals (0.15×0.1×0.05 mm3) changes from colorless to brown
group.Moreover,theorderedOfnmoleculesareintercalatedbetween rapidlywithin4s,accompaniedbythefadingofgreenfluorescence.
two layers of disordered 3Abf molecules with the larger interlayer Concurrently,thecrystalsshowadistinctphotosalient(splittingand
spacingdistanceof3.381Åandoverlappingareaofnearly95%,form- jumping)effectinresponsetoUVlight.Whenthedurationoflight
ing a mixed stacking structural motif (DADADA) through π−π irradiationtimerangeof0–2minutes,the3Abf-Ofncrystalsundergo
interactions41 (Fig. 2c). Such alternating stacks column enhances fastandobvioussplittingactuation,andbreakdownintoindividual
strong electronic coupling44, promoting PET from 3Abf to Ofn. In microcrystalssuddenly,someofwhichjumpedtorandomdirections
addition,adjacent3AbfmotifsareinterconnectedviaC-H···NandN- beyondtheilluminatedareaandremainunchangedthereafter,sug-
H···C hydrogen bonding interactions in a staggered arrangement gestingthatsuchcrystallinematerialexhibitsaspecificresponseto
(Fig.2d),withthedihedralangleof40.59°and42.63°(Supplementary UVlight.Notably,themicro-sizedcrystallinefracturesurfacesemit
Fig. 1). Likewise,neighboring Ofn molecules are linked byF···F con- brightgreenfluorescenceunderUVlight,whichrapidlydiminishes
tacts,withnosignificantinterplanartwistbetweenadjacentnaphtha- and eventually disappears completely, implying that the high-
lenerings(SupplementaryFig.2).Bothmolecularcomponentsfurther contrast photochromic transformation of the crystals occurs con-
extendinto2Dsupramolecularlayersinfinitelyalongthec-axis(Sup- tinuouslythroughouttheentireilluminationprocess.Furthermore,it
plementaryFig.3).Furthermore,thephasepurityandcrystallinenat- isobservedthattheneedle-likefragmentedcrystalretainsacurved
ure of the as-prepared 3Abf-Ofn during crystallization can be morphologywithanangleof10.16°withoutrevertingtoitsoriginal
elucidatedbypowderX-raydiffraction(PXRD)analysis,whichshow straightshapeuponremovalofthelightsource,indicatingacertain
goodagreementwiththesimulatedpatternfromsingle-crystalstruc- degreeoflight-inducedplasticdeformation(SupplementaryFig.8).
ture,theintense(002)diffractionpeakindicatesapreferredorienta- The light-induced mechanical motion and photochromic behavior
tion (Fig. 2e). Fourier transform infrared (FT-IR) spectra indirectly can also be presented in crystals of different sizes with varying
responsespeeds(SupplementaryFig.9),whicharelargelyrelatedto radicals during the light-induced electron transfer process for the
variousinternalandexternalfactors,suchasinternaldefects,crystal visible coloring process. Furthermore, 3Abf-Ofn powder exhibits a
size, light intensity, as well as morphology45–48. Crucially, thermal distinct decrease in fluorescence intensity upon UV irradiation
effects can be excluded as the primary driver of these responses. (Fig. 3d and e), consistent with their decreasing trends in both
Differential scanning calorimetry (DSC) result (Supplementary fluorescence lifetimes from 4.80 to 3.78ns (Fig.3f, g) and fluores-
Fig. 10) indicates that the as-prepared 3Abf-Ofn crystals have a cence quantum yield (PLQY) (Supplementary Figs.13 and 14). The
meltingpointof139°C,andnomorphologicalchangesareobserved quenchingisattributedtothePETgeneratinganon-emissiveradical
whenthecrystalsareheatedbelowthistemperature(Supplementary state49, as well as the self-absorption effect50. This is further sup-
Fig.11).Moreimportantly,themaximumtemperatureofthecrystals portedbythenotablespectraloverlapbetweentheUV-Visabsorp-
reachedabout42°CundercontinuousUVirradiation.Therefore,it tion bands of photoproducts during irradiation and fluorescence
can be concluded that the mechanical motions and photochromic emissionspectraofthepristine3Abf-Ofnmaterial.Furthermore,the
behavior of 3Abf-Ofn crystals are primarily driven by the direct yellowpowderbyshort-termUVirradiationcanberestoredtothe
influenceofUVlightstimulationratherthanthermal-inducedstruc- initial state upon heating to 95°C (Supplementary Fig. 15). The
turalchanges.
thermal decomposition as a contributing factor during the fading
Unlikethedynamicmechanicalbehaviorofcrystalline3Abf-Ofn processcanbeexcludedbasedonthedecompositiontemperatureof
atthemacroscopicscale,thepowdersampleremainsstaticuponUV 3Abf-Ofn. Moreover, the PXRD and FT-IR spectra after thermal
light irradiation, confirming that the fine particles prevent the treatment are nearly in agreement with those before the photo-
accumulationofenergyduetosizeeffect48.Itisworthmentioning chromic process (Supplementary Figs. 16, 17), indicating no sig-
thatphotochromicprocessesareretainedfor3Abf-Ofnpowder,with nificant structural changes during this process. Importantly, the
thepowdersamplestransitioningfromwhitetodeepyellowrapidly pronounced decrease in EPR signal intensity after heat treatment,
within 20s (Fig. 3b), accompanied by the emergence of a new suggestingthephotogeneratedradicalscanbequenched,whichis
absorptionbandinthescopeof370-450nm(SupplementaryFig.12), directly correlated with the color fading and fluorescence
indicatingtheformationoflight-inducedspecieswithradicalchar- recovery49,51.Furthermore,repeatedUVirradiationofthethermally
acter.Correspondingly,a pronouncedsignalwith g=2.004canbe treated3Abf-OfnsamplesleadstothereappearanceoftheEPRsignal
detected for the colored sample after irradiation in electron para- and a darkeningofthe samplecolor(SupplementaryFig.18),con-
magneticresonance(EPR)spectra(Fig.3c),whileonlyaweaksignal firmingthatthecolorrecoveryisprimarilyattributedtotheregen-
is observed before irradiation, verifying the generation of free eration of photogenerated radicals upon irradiation. However,
followingprolongedUVirradiation,the powder undergoesa color after sufficient irradiation for 2h, making it difficult to resolve
darkening upon thermal treatment (Supplementary Fig. 19) and photochemicalreactionproductsbysingle-crystalX-raydiffraction.
exhibitsnewdiffractionpeaksinthePXRDpatterns(Supplementary After numerous attempts10,14,53–55, the final photoproduct can be
Fig.20),owingtotheactiveradicalsthatmaytriggersidereactions52. obtained successfully through solution recrystallization and con-
Meanwhile,theintensityofUV-Visabsorptionpeaksdecreasessig- firmedtheformationofonlyBfa.
nificantlyuponheating,approachingtheinitialspectralprofilesprior ThephotoreactioncompoundBfaiscrystallizedinthemonoclinic
toirradiation(SupplementaryFig.21),indicatingthecoexistenceof space group P2/c, as summarized in Supplementary Table 1. The
1
thereversibleradical-basedoriginalreactantsandphotoproductsin adjacentBfamoleculesaretightlyconnectedthroughstrongC-H···π
a mixed phase. In contrast, mechanically grinding achieves good interactions (2.862 and 2.887Å), with a dihedral angle of 47.12°,
cyclingstabilitywithoutalteringthecrystallinephase,asevidenced forminganorderednetworkstructurealongthebaxis(Fig.4a,and
byPXRDpatterns(SupplementaryFig.22)thatareconsistentwith Supplementary Fig. 26). The highest occupied molecular orbital
those of the light-irradiation product. This structural recovery is (HOMO)andthelowestunoccupiedmolecularorbital(LUMO)ofBfa
accompaniedbyasignificantincreaseinbluefluorescenceintensity arepredominantlydistributedacrosstheconjugatedbackbone.The
observabletothenakedeye(SupplementaryFig.23).
calculatedenergygapofBfa(3.270eV)islowerthanthatofthe3Abf-
Mechanisminvestigationforphoto-responsiveproperties Ofnmolecules(3.490eV)(Fig.4b),furthercorrespondingtoexperi-
Tofurtherclarifytheoriginofthephotochemicalreactionprocess mentalevidenceddemonstratingthevisiblelightabsorptioncapacityof
inthe3Abf-OfncocrystalduringUVlightirradiation,variousstruc- the3Abf-Ofnundercontinuousillumination.Inaddition,theintensity
turalcharacterizationtechniqueswereperformed.SCXRD,serving ofthepeakat5.5ppmin1HNMRspectraexhibitasignificantchange
asthemostdirectandpowerfultooltodeterminepotentialstruc- followingUVlightirradiation,indicatinganalterationinthechemical
tural changes, was further performed on freshly split crystals environmentofthehydrogenatomsof-NH₂(SupplementaryFig.27).
maintained in high quality with shorter UV irradiation time. After IntheFT-IRspectra,theintensityof-NH₂stretchingvibrationpeakat
20soflightirradiation,the3Abf-Ofncrystalexhibitsanexpansion 3388cm-1 gradually weakens upon prolonged UV irradiation time
ofapproximately0.25%alongtheb-axisandacontractionofabout (Fig.4c,andSupplementaryFig.28),suggestingachangeinthecon-
0.34% along the c-axis. Additionally, the dihedral angle between tentof-NH₂groupsandinvolvementinthephotochemicaltransfor-
3Abf and neighboring Ofn molecules decreases from 6.91°, and mation. Furthermore, new diffraction peaks appear in the PXRD
6.86° to 3.76°, and 4.65°, respectively (Supplementary pattern(SupplementaryFig.29),whichcorrespondwelltothesimu-
Figs.24and25).Thisanisotropiclatticedeformationindicatesthat latedpatternoftheBfaproduct.High-resolutionmassspectrometry
significantrelative rotation and structural rearrangement between (HRMS) further confirms the formation of the final product Bfa
moleculesoccurduringthephotoinducedprocess,generatingand (C₂₄H₁₄N₂O₂),withadetectedm/zvalueof363.111matchingthecal-
graduallyaccumulatinginternalstresswithinthelattice. However, culatedexactmass.Moreover,therelativeabundanceofBfamarkedly
the crystal quality of 3Abf-Ofn has been significantly deteriorated increasesfrom20%tonearly100%uponcontinuousirradiationfor2h
(Supplementary Fig. 30). Subsequent X-ray photoelectron
spectroscopy(XPS)analysisrevealsthatthesignalintensityoftheC-F character,leading to localized structuralinstability. Uponlightsti-
bonddiminisheswithincreasingUVirradiationtime(Fig.4d,e,Sup- mulation, energy is rapidly transferred, inducing swift molecular
plementaryFigs.31and32),consistentwiththereleaseofOfnduring twisting in these disordered regions, thereby initiating a drastic
photoinducedprocess,whichcontributestothestabilityofthepho- phasetransition.Duringthephasetransition,theextremeproximity
toproductBfa.
ofadjacent3Abfunitsfacilitatesaradicalcouplingreaction.Mean-
To elucidate the reaction pathway from 3Abf-Ofn to Bfa, the while, Ofn is no longer stabilized within the lattice due to loss of
control experiments with alternative electron donors (1-aminodi- structuralcompatibility.Givenitslowmeltingpointandhighvapor
benzofuran (1Abf) and 2-aminodibenzofuran (2Abf)) and acceptors pressure58, Ofn readily sublimes even at room temperature, thus
(1,2,4,5-Tetracyanobenzene (Tcnb), 3,4,5,6-Tetrafluorophthalonitrile facilitating its escape through sublimation as the temperature
(Tfpn), and 3,4,5,6-Tetrachlorophthalonitrile(Tcpn))under identical increasesunderUVirradiation.Whentheaccumulatedinternalstress
conditions are conducted. Bfa compounds can be detected (m/z is abruptly released, the crystal lattice is broken, giving rise to
363.111) by HRMS upon UV irradiation of 1Abf–Ofn (Supplementary observablemechanicaleffectsthatultimatelyleadtoanamorphous
Fig. 33) and 2Abf–Ofn (Supplementary Fig. 34), which demonstrate state, marking the transformation from a metastable to a stable
that the strategy can be extended to more systems. EPR results of state13,46. For the localized plastic deformation observed in a few
1Abf–Ofnand2Abf–OfnrevealthepresenceofradicalsignalsbyPET, samples,whichcanbeattributedtoarelativelygradualstressrelease
accompanied by photochromic behaviors (Supplementary thatdoesnotreachtheenergythresholdnecessarytoinducebrittle
Figs.35–37).Notably,thereactionproceedsefficientlyevenundera fracture. At the microscopic level, this behavior originates from
nitrogen atmosphere, as evidenced by both Bfa product formation sudden anisotropic changes in the unit cell48. The molecular rear-
(SupplementaryFig.38)andphotochromicbehavior(Supplementary rangements of 3Abf-Ofn at transition states cause lattice volume
Fig.39),confirmingthatthisreactionisnotaconventionaloxidative expansion,whichcanreachupto84.8%(from909.01to1679.84Å3).
couplingpathwaywithmolecularoxygen56,57.However,itisfailedto The anisotropic expansion of the crystal occurs rapidly to drive
observecolorchangesandyieldazocompoundsin3Abf-Tcnb,3Abf- macroscopicmotion.Importantly,thestructuraldefectenvironment
Tfpnand3Abf-Tcpn(SupplementaryFig.40),underscoringthecrucial formedbymoleculardisordering,tosomeextent,facilitatesmole-
roleofOfnindrivingthereaction.Basedontheexperimentalfindings, cularrearrangement,therebycreatingfavorableconditionsforthe
we propose the reaction mechanism. Upon UV irradiation, photo- photo-inducedmechanicalresponse.
induced electron transfer from the electron-donor 3Abf to the
electron-acceptor Ofn generates radicals, which subsequently Photophysicalpropertiesfor3Abf-OfndopedintoPMMAfilm
undergointermolecularN–Ncouplingtoformtheazobenzenederi- Considering the excellent photoresponsive properties of the
vative Bfa. Density functionaltheory(DFT) calculations (Fig. 4f) are 3Abf–Ofn cocrystals and the practical requirements for processa-
performedtosupportourproposedreactionpathway.Uponphoto- bilityandintegrabilityofsolid-statefunctionalmaterials,weincor-
excitation, 3Abf-Ofn enters the singlet excited state, followed by porated 3Abf-Ofn powder into polymethyl methacrylate (PMMA)
intermolecular electron transfer to generate radical species. Subse- polymer matrices in dichloromethane to improve their overall
quently,the-NH2•+of3Abfdeprotonatestoform-NH•,resultingina applicability.ThePXRDanalysisindicatethat3Abf-Ofncomponents
reductionofthesystemenergyto0.89kcal/mol.Thegeneratedradical areeffectivelydopedintothePMMAformingamorphousstates,with
thenparticipatesinN–Ncouplingprocesstoyieldanazo-linkeddimer, nosignificantphaseseparation(Fig.5a).XPSdemonstratesthedif-
andfinalproductenergy(1.43kcal/mol)islowerthantheinitialstate, ferent functional groups between 3Abf-Ofn and the PMMA matrix
demonstrating that PET-assisted coupling reaction of 3Abf-Ofn is (SupplementaryFigs.47and48).Furthermore,the3Abf-Ofn@PMMA
thermodynamicallyfavorable.
filmshowsdistinctiveopticalcharacteristics,inadditiontopreser-
The photochemical reactivity of the 3Abf–Ofn cocrystal is ving the photochromism (Supplementary Fig. 49) of the pristine
intrinsicallylinkedtoitsmacroscopicphotomechanicalresponse.To 3Abf-Ofnpowder.Specifically,theinitialfluorescencesignalisweak,
further uncover the origin behind the photoinduced mechanical however,thefluorescenceintensityincreasesbyapproximately10-
motion,takingthepristine3Abfand3Abf-Tcpncocrystalsystemsas foldaftercontinuousirradiationfor20s(Fig.5bandc),andfluor-
an example. Under identical irradiation conditions, both pristine escencelifetime slightlyincreasesfrom3.93nsto4.00ns(Supple-
3Abf and 3Abf-Tcpn cocrystals remain stable macroscopic mentaryFig. 50), revealing a clear phenomenon ofphotoactivated
morphologies (Supplementary Figs. 5 and 41), and their photo- fluorescence enhancement. The behavior can be attributed to the
responsepropertiesaredistinctlydifferentfromthoseofthe3Abf- intrinsic aggregation-induced emission (AIE) of 3Abf-Ofn (Supple-
Ofnsystem(SupplementaryFigs.42and43).SCXRDanalysisfurther mentaryFig.51)and UV-induced transientpolymerchainmobility,
reveals the self-assembly patterns and intermolecular interactions facilitatingmolecularorderedaggregatescollectively6,59–61.Interest-
are key factors influencing photochemical processes. Pure 3Abf ingly, when different wavelengths of visible light are employed as
adoptsaclassicherringbonepackingmotifdrivenbyC–H⋯πinter- excitationsources,the3Abf-Ofn@PMMAfilmdisplayspronounced
actions(SupplementaryFig.44a),theclosestN⋯Ndistanceisaslong EWDE(Fig.5d),withthewavelengthsofemissionspectraspanning
as7.312Å(SupplementaryFig.44b),indicatingmoleculesstruggleto from450nmto680nm,correspondingtheirCIEcoordinatesfrom
achieve close-range cooperative motion through slip or rotation, thebluetotheredregion(SupplementaryFig.52),indicatingabroad
preventing observable macroscopic deformation. The 3Abf-Tcpn tunabilityinluminescence,whichexhibitpromisingapplicationsin
cocrystalspresentD-Aarrangementpattern(SupplementaryFig.45), smartdisplays,multicolorfluorescentdevices,andopticalencoding
but its structure is stabilized by hydrogen bonds interactions (N- technologies.UponprolongedUVirradiation,asignificantreduction
H⋯N, C-H⋯N, and N-H⋯F) that form rigid dimers units (Supple- in fluorescence intensity is observed for 3Abf-Ofn@PMMA film
mentaryFig.46),whichfurtherassembleintohighlyparallel,tightly (Fig. 5e), with the PLQY decreasing from 4.32% to 3.90% (Supple-
packed DADA columns. This strong hydrogen-bonding network mentaryFig.53).Thefluorescenceattenuationisattributedtopho-
rigidlylocksmolecularconformation andsignificantlyrestricts the tochromisminducedbyradicalformation,asevidencedbyenhanced
degreesoffreedomformolecularmotionintheexcitedstate.Forthe visible-lightabsorption(Fig.5f)andincreaseinEPRsignalintensity
as-prepared 3Abf-Ofn crystals, intermolecular interactions are (Supplementary Fig. 54). Additionally, the 1Abf molecules are iso-
dominated by weak interactions (C–F⋯H, F⋯F and π-π) contacts, structuralsystemsof3Abf.1Abf–Ofnpowderexhibitsphotophysical
lackingstrongdirectionalhydrogenbondconstraintsbetween3Abf properties analogous to those of 3Abf–Ofn (Supplementary
and Ofn. This packing arrangement displays a loosely packed Figs.55–59).Correspondingly,the1Abf-Ofn@PMMAfilmsalsoshow
photoactivated fluorescence enhancement effect followed by irradiation of varying durations to different regions,multi-level and
quenching upon prolonged irradiation, as well as EWDE (Supple- programmableopticalresponsescanbeachieved.Forinstance,aftera
mentary Figs. 60–63). In contrast, neither significant fluorescence 5sirradiationoftheheartregion,nonoticeablechangesareobserved
enhancement nor EWDE is detected in 3Abf-Tcpn@PMMA and underdaylight.However,dueto
3Abf@PMMA films, and the overall fluorescence intensity is weak, UV light-induced fluorescence enhancement effect of 3Abf-
respectively (Supplementary Figs. 64-66). Supplementary Ofn@PMMAfilm,thisregionexhibitsclearandbrightbluefluores-
Figs. 67–69 clearly indicate that the photoresponse properties of cence, forming a time-resolved fluorescence intensity anti-
films are related to the inherent optical properties of the dopant counterfeitingmark.Meanwhile,theuseofexcitationlightsources
molecules themselves. Replacing the PMMA matrix with polyvinyl at different wavelengths enables multi-channel optical responses,
alcohol(PVA)matrixinaqueoussolution,both3Abf-Ofn@PVAfilm providinganadditionalsecuritydimensionforinformationencryp-
and 1Abf-Ofn@PVA film display only conventional photochromic tion and significantly enhancing confidentiality. When the peace
behavior, with a narrower excitation-dependent emission range dove region is exposed to UV light for a longer time, a significant
(Supplementary Figs. 70–74). XPS spectra of 3Abf-Ofn@PVA show photochromicresponseoccurs,resultinginavisiblecolorcontrast
the presence of C-O-C and C-O-H bonding signals at 533.38, and under natural light. The entire film is exposed to 20s of UV light,
532.35eV,respectively(SupplementaryFig.75).Thestrongbonding which falls in the fluorescence enhancement response window.
interactionsrestrictmolecularflexibilityandpromotefeweremissive Undertheseconditions,thelocalizedfluorescencesignalintheheart
states. Furthermore, we further fabricated 3Abf-Ofn doped films region is gradually masked by the enhanced background fluores-
usingotherpolymermatrices,includingpolylacticacid(PLA),poly- cence,effectivelyconcealingand fadingthe first-levelinformation.
amide(PA),andpolyvinylpyrrolidone(PVP)indichloromethane.The UponfurtherprolongingtheUVexposure,thepeacedovepattern
resultsrevealthatsimilarlight-regulatingbehavior(Supplementary gradually fades, ultimately erasing the information and enabling a
Figs. 76–80) to that in 3Abf–Ofn@PMMA film, demonstrating that system reset. Furthermore,thefluorescentvisualizationproperties
the photoactivated aggregation induced luminescence mechanism of3Abf-Ofn@PMMAcanbeappliedindigitalinformationencryption
exhibits excellent reproducibility in various hydrophobic polymer system(Fig.6b).Thecorrectpassword3113isonlyrevealedunder
matrices. fluorescent mode after UV irradiation 20s. In contrast, the initial
mask encoding is 1331, which is clearly visible under daylight and
Applications servesasmisleadingsurface-levelinformation.Authorizedpersonnel
Based on tri-state fluorescence switching in 3Abf-Ofn@PMMA film canretrievethetruepassword3113viafluorescentimagingunderUV
materials,thepotentialapplicationsinmulti-levelanti-counterfeiting illuminationafterthedesignatedexposuretime.Continuedirradia-
andinformationencryptionareinvestigated.AsillustratedinFig.6a, tionfor240sinducesfluorescencesaturationacrosstheentirearea,
peacedoveandheart-shapedmasksareplacedon3Abf-Ofn@PMMA transitioningthedisplayto8888,aninterferencepatterndesignedto
filmsamples.BeforeUVirradiation,thefilmremainstransparentwith preventunauthorizedaccess.Moreover,thephotochromicmaterials
novisiblepatternsunderbothdaylightandUVlight,demonstrating 3Abf-Ofn and 1Abf-Ofn can be extended to functional decorative
excellent properties for information storage. By applying UV applications by embedding them into a mold (Fig. 6c and
SupplementaryFig.81).UnderUVirradiation,3Abf-Ofnchangesfrom
white to yellow, while 1Abf-Ofn turns brown. With prolonged UV
illumination, 3Abf-Ofn and 1Abf-Ofn powders exhibit a noticeable
color gradient, showing excellent visual appeal. Importantly, the
colors can be restored to their initial states through mechanical
pressure,enablingreversiblecolorswitching.

Methods
Materials
3-Aminodibenzofuran(3Abf,98%),1-Aminodibenzofuran(1Abf,98%),
2-Aminodibenzofuran(2Abf,98%),Octafluoronaphthalene(Ofn,96%),
1,2,4,5-Tetracyanobenzene (Tcnb, 97%), 3,4,5,6-Tetra-
fluorophthalonitrile(Tfpn,98%),and3,4,5,6-Tetrachlorophthalonitrile
(Tcpn,98%)werepurchasedfromcommercialsuppliers(Aladdinand
TCI)andusedwithoutfurtherpurification.

Preparationof3Abf-basedcocrystals.Intypicalprocesses,the3Abf-
Ofn,and3Abf-Tcpncocrystalswereobtainedbyslowevaporationina
methanol/dichloromethanesolution(v/v=1:1,30mL)withtheinitial
molarratiosofthetwocompositionsin1:1.Thesinglecrystalscanbe
obtainedwithin10-15days.

PreparationofPMMA,PLA,PA,andPVPfilms.20mg3Abf,20mg
3Abf-Ofn,20mg3Abf-Tcpn,and20mg1Abf-Ofnpowderwerethor-
oughly mixed with polymer-dichloromethane solution, respectively,
andthenstirredtheresultingmixturefor30mintoensureuniform
homogeneity. Following vigorous stirring, the well-mixed mixture
solutionwasdirectlydepositedontoacleansubstrateandallowedto
evaporateslowlytoformuniformfilms.

PreparationofPVAfilm.20mg3Abf-Ofn,20mg1Abf-Ofnpowder,
and500mgPVApolymerwerethoroughlyaddedintoa10mLwater
solution,respectively,andthenstirredandheatedtheresultingmix-
tureat80°Cforatleast12htoensureuniformhomogeneity.After
vigorous stirring, the homogenously mixed solution was directly
depositedontoacleansubstrateandallowedtoevaporateslowlyto
formuniformfilms.

Computationaldetails
Thedensityfunctionaltheory(DFT)calculationswereperformed
using the Gaussian 16 program package. All geometric optimiza-
tions and energy calculations were carried out with the m062x
hybrid functional, combined with the 6-311++g (d,p) basis set,
containingthesolvent(dichloromethane)effectmodeledwiththe
solvation model of density (SMD)method. Vibrational frequency
analyses were performed to verify that all optimized geometries
correspondtoenergyminima,freeofimaginaryfrequencies.For
accelerating the self-consistent field (SCF) convergence and
improving calculation efficiency, the extra-quick convergence
(XQC) algorithm was adopted (controlled by the SCF=XQC key-
word). All structures were optimized until the convergence cri-
teria for geometries and energies werefullysatisfied.

Characterizations
PXRDpatternwereperformedonX-raydiffractometer(Rigaku,18kW/
D/Max2550VB/PC,CuKαradiation,λ=1.5418Å,40kV/100mApower)
atroomtemperature.SCXRDdatawerecollectedonaBrukerAPEX-II
CCDdiffractometerwithCuKαradiation(λ=1.54178Å)at298K,and
thestructuresweresolvedwithOlex2.FT-IRweremeasuredusingthe
WQF-530 instrument. UV-Vis absorption spectra were taken using
a Shimadzu UV2700 (Japan). 1H NMR spectra were obtained using a
Bruker500MHzSpectrometer.EPRwasmeasuredwithaJES-320JEOL
RESONANCEsystem(microwave9.422GHz).XPSmeasurementswere
performedattheThermoScientificK-Alpha(America)attheSLS.FL
spectra were characterized using a Shimadzu RF-6000 instrument.
HRMS is collected on a Thermo Scientific Q Exactive Orbitrap. The
photoluminescence lifetime (τ) and photoluminescence quantum
yield(PLQY)weremeasuredonanEdinburghFLS1000spectrometer.
TGA/DSCanalyseswereobtainedusingaRigaku,withtherateof10°C/
min in flowing nitrogen. Crystal morphology modelling and corre-
spondingMillerindicesofdominantfacesarepredictedthroughthe
Bravais–Friedel Donnay-Hulme (BFDH) method in the Mercury soft-
warebasedonsinglecrystalXRDdata.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript reports the design and characterization of an organic co-crystal system (3Abf-Ofn) exhibiting both dynamic photosalient and static photochromic behaviors, along with light-induced fluorescence modulation when embedded into a PMMA matrix. The authors claim to have revealed a new light-driven structural transformation mechanism involving guest molecule release and diazetidine formation, which could contribute to multifunctional luminescent material design. The topic is interesting and potentially significant to the field of light-responsive organic materials. However, several critical scientific and presentation issues must be addressed before the manuscript can be considered for publication in Nature Communications.\n1. Figure 1 fails to show how the crystal packing change correlates with photochromism and light-induced cracking. The schematic should illustrate the structure–function relationship and the fate of Ofn molecules after UV irradiation. The mechanism for fluorescence quenching under UV light also needs clarification.\n2. Please clarify whether the color change arises from radicals generated by the reactant or the photoproduct. Supporting evidence such as EPR spectra would help.\n3. The fluorescence enhancement and quenching are attributed to AIEE, but no data prove that 3Abf exhibits AIE. Provide solution/solid-state experiments or discuss whether the PMMA acts as a barrier to molecular relaxation.\n4. Explain the mechanism of color recovery upon heating. Structural or spectroscopic evidence of the phase transition is needed.\n5. Clarify the reason for EWDE in 3Abf-Ofn@PMMA and its absence in 3Abf-Tpn@PMMA. Define “Tpn” and explain why changing the polymer matrix removes EWDE. Also, check whether the fluorescence enhancement–quenching process persists with other matrices.\n6. “Fluorescence lifetime decreases from 3.93 ns to 4.00 ns” is incorrect. Please revise.\n7. Figure 3: Crystal images unclear—provide higher-resolution photos.\n8. Figure 22: Enlarge key NMR peaks to better show new product formation.\n9. Figures S15–S16: Use separate real images for heating/pressure recovery, not identical ones.\n10. References: Add key missing works — Adv. Mater. 2025, 37, 2504417; Angew. Chem. Int. Ed. 2025, e202506549; Chem. Soc. Rev. 2024, 53, 10312.", "reviewer_2": "In this study, the authors constructed an organic cocrystal that exhibits both dynamic motions and photochromic properties. The crystal was further integrated into a polymer film to demonstrate information encryption technology based on its photochromic behavior. Although the dynamic response relies on an unconventional coupling reaction, the study lacks an in-depth investigation into the mechanism of this new reaction. The novelty of this work is not immediately apparent, as the integration of mechanical dynamic motion, photochromism, and photoluminescence changes has been commonly observed. (ACS Appl. Mater. Interfaces 2020, 12, 14, 16856–16863. J. Mater. Chem. C, 2023,11, Adv. Funct. Mater. 2023, 33, 2212886. J. Am. Chem. Soc. 2023, 145, 45, 24636–24647. Chem. Soc. Rev., 2024,53, 6636-6653. 4375-4383. J. Am. Chem. Soc. 2024, 146, 47, 32757–32765. Latest Article: Stiffening Organic Crystals through Polymerization Using Visible Light) Furthermore, the mechanism explanations are neither rigorous nor sufficient. The current report lacks significant, unique findings, novel insights, or the fundamental advances required for publication in Nature Communications.\nMajor issues:\n1. In page 4, line 114. Miller indices are referenced; authors are advised to specify the simulation methods used. Furthermore, it is recommended to use a single-crystal X-ray diffraction for more accurate determination of the Miller indices, which is crucial for revealing the reaction mechanism and mechanical behavior.\n2. The portion regarding the crystal's fluorescence response to acid stimulation does not significantly contribute to the main focus of the article, as it appears to digress from the central theme. Therefore, I recommend removing this section.\n3. In page 5, line 139, it is recommended that the TGA data of the 3Abf and Ofn be included as well.\n4. In page 6, line 163-165, through microscopic observation, it is insufficient to visually conclude that the crystal exhibits no thermal response behavior. It is recommended to perform DSC testing to provide supplementary evidence.\n5. In page 7, line 186-188, The powdered sample loses its macroscopic mechanical response, primarily because such mechanical behavior is governed by a size effect—the small dimensions prevent the accumulation of sufficiently large strain to drive crystal deformation and fragmentation. The term \"aggregates\" mentioned here may easily lead to ambiguity; could it refer to changes in the packing structure? Reference: Chem. Rev. 2015, 115, 22, 12440–12490.\n6. In page 7, line 201-206, the reversible process of heating- or mechanical stress-induced fluorescence recovery needs to be demonstrated. This process may be more complex than initially assumed, as it may involve double-bond cleavage and eutectic reassembly rather than a simple mechanism.\n7. In page 9, line 226-228, the authors mention that they obtained a single crystal after the photoreaction, which allowed single crystal structure was directly carried out by single crystal X-ray. However, the photoresponsive behavior of this crystal is accompanied by fragmentation and disintegration. It would be critical to ascertain the three-dimensional size of the single crystal used for the structural analysis, as well as the light power—suitable for such analysis—was acquired.\n8. The melting point of Ofn is approximately 80 °C, and the authors also mention that the crystal temperature does not exceed 50°C after illumination. Given such a high melting point, along with the constraints imposed by the lattice and intermolecular interactions, it is puzzling how Ofn can escape while simultaneously yielding high-quality single crystals of Bfd. Furthermore, according to the ESP calculations of Bfd, there is a clear electronic complementarity with Ofn, suggesting the presence of significant electrostatic interactions. So, what mechanism enables Ofn to be released from the lattice? After Ofn overflowed from the lattice, does it sublimate and leave or recrystallize? That is, in what form does it exist?\n9. Figure S22 is small. Additionally, the figure indicates the use of DMSO-d6 as the deuterated solvent, while the caption states that CDCl3 was used. The proton NMR peaks should be assigned accordingly. Furthermore, the chemical shift at approximately 5.5 ppm should correspond to the -NH2 group, which shows no change before and after light irradiation—neither a reduction in peak area nor the appearance of new peaks. This does not support the occurrence of a chemical reaction. Furthermore, the high-resolution mass spectrometry data indicate only trace amounts of Bfd, making it difficult to believe that such a minimal amount of reaction product could yield high-quality single crystals suitable for X-ray diffraction analysis.\n10. In page 10, line 270-276, the authors used pristine 3Abf and 3Abf-Tpn as reference systems to elucidate the distinctive mechanical motion of the 3Abf-Ofn cocrystal. It is recommended that the authors explain the origin of the distinct mechanical properties exhibited by 3Abf-Ofn from the perspectives of crystal packing and intermolecular interactions.\n11. In page 12, line 317, does the fluorescence lifetime change from 3.93 to 4.00 ns, or from 4.00 to 3.93 ns? According to Supporting Information Figure 36, the fluorescence lifetime should exhibit an increasing trend, which differs from the previously observed decrease in both fluorescence intensity and lifetime in the crystal (Figure 3c–f). What is the reason for this discrepancy?\n12. In page 12, line 319, the authors doped cocrystal powders into a PMMA matrix. How exactly can UV irradiation induce the movement and aggregation of molecules within the cured polymer matrix, given that 3Abf and Ofn were incorporated in crystalline form rather than as freely mobile, unconstrained molecules? Reference: Adv. Funct. Mater. 2024, 34, 2411584. Additionally, the PMMA matrix thin films were prepared by mixing PMMA and the cocrystal powder in a dichloromethane solution. Does the cocrystal dissolve in dichloromethane? Furthermore, what is the color variation in the PMMA matrix films containing only 3Abf?\nMinor issues:\n1. In page 6, line 158, the term should specifically refer to “light-induced plastic deformation” rather than the general “plastic deformation”, as the latter may cause ambiguity. “Plastic deformation” typically describes the mechanical properties of materials. To avoid any potential misunderstanding, please revise it to \"light-induced plastic deformation.\"\n2. In page 5, line 125, to be provided in the supporting information: How is the overlapping area determined?\n3. In page 5, line 125, “a sandwich-like structural motif” is more accurately described as “mixed stacking”, (−DADADA−). Please refer to Angew. Chem. Int. Ed. 2024, 63, e202416181 for proper description.\n4. In page 5, line 128-130, the authors note that the two dihedral angles are “40.59 and 48.72.” It would be helpful to indicate in the crystal structure diagram which specific molecular dihedral angles these values refer to. The text mentions dihedral angles between adjacent molecules; however, for example, 3Abf molecules have neighboring molecules along both the b- and c-axes. Additionally, in Figure 2e, the Ofn molecules connected via F···F interactions appear to be parallel, rather than exhibiting a dihedral angle of “48.72.”\n5. In page 5, line 132, what is the intended purpose of the ESP simulation? Is it merely to demonstrate the existence of charge transfer, thereby contributing to subsequent mechanistic explanations? However, the electron spin resonance (ESR) spectroscopy results indicate no radical signals before illumination, suggesting that the formed structure is not a charge transfer cocrystal and that no charge transfer occurs. If these simulations are redundant and fail to provide meaningful insights, they should not be included merely to bolster the content.\n6. In page 4, line 121, “the disordered Ofn units”. However, in the crystal structure, the 3Abf units are disordered, the Ofn units are ordered.\n7. In page 5, line 145, it is suggested to provide the power of light.\n8. In page 5, line 146, it is mentioned that the initial crystal exhibits green fluorescence, whereas in page of 7, line 177, the initial crystal is described as having blue fluorescence. I am uncertain whether this represents a potential inconsistency in the description.\n9. In page 11, line 293-295, directly comparing the changes in unit cell volume before and after is an incorrect approach.\n10. In the main text, the terminology for figure citations is inconsistent, with some instances using \"Figure x\" and others using \"Fig. x\". Additionally, there are erroneous citations in the figure sequence; for example, \"Fig. 3e\" is misreferenced as \"Fig. 2e.\"", "reviewer_3": "The manuscript reports an intriguing cocrystal which exhibits photomechanical response. The results are of interest however raise more questions answers. After careful reading of the manuscript it can be realized that the manuscript lacks focus and is not supported by careful narration and explanations. Therefore, I don’t recommend the publication of manuscript in Nat. Commun. For following general and specific reasons:\nGeneral observations:\n1. Highlight of work is solid state dimerization of 3Abf molecules within a crystal on exposure to UV radiations. This is interesting, however can the strategy be extended to more systems? What is the net chemical reaction leading to product formation and mechanical response is not explained clearly.\n2. The introduction is not focused and doesnot provide a definite idea of developments in the area, instead is more generalized to describe cocrystals, which of course is not the focus of work.\n3. The manuscript is not written carefully and leaves many questions unanswered. The language shall be taken care of so shall be many claims, which are either contradict, incorrect or unsubstantiated.\nSpecific comments:\nIntroduction: In generally introduction is not convincing and lacks the purpose. It needs to be reworked with better connection to current work, essentially supported by relevant literature.\nI-1: The language used at multiple stages of manuscript is complex and difficult to follow and the claims are not substantiated. For example “Hence, it is crucial to design and develop a multifunctional crystalline materials system capable of sensing the external environment through multi-level information output driven by distinct action mechanisms. Furthermore, it remains a challenge to convert the photoinduced dynamic mechanical motion of responsive materials into static luminescent modes within the same system to meet diverse material requirements. However, dynamic crystalline materials that exhibit only single mechanical response characteristics struggle to meet the diversified demands of technological advancement” and many more.\nI-2: “Sun et al. designed a series of biodegradable ferroelectric cocrystals of cholesterol-methanol and cholesterol-ethanol through the solvent effect.” These are better described as solvates than co-crystals. Of course there are better and strong examples of co-crystals resulting in improved conducting, optical and pharmaceutical properties.\nI-3: “Photochromic fluorescent materials refer to photosensitive substances that exhibit changes in color or fluorescent properties.” This is not true as photochromic materials can be described like that not photochromic fluorescent materials.\nI-4: “In this work, we reported the example of photosensitive effect and photochromism in same organic molecular cocrystals, which are co-assembled by 3Abf and Ofn building blocks driven by hydrogen bond interaction (Fig. 1).” The co-crystals are based on pi-interactions rather than hydrogen bonds.\nResults and Discussion\nR-1: Symmetry unit = asymmetric unit\nR-1: one ordered Ofn molecule = ? ; molecular order of 3Abf has been degraded during = ?; supramolecular molecular structures around the disordered 121 Ofn units in the crystal lattice = ?\nR-3: How can FT-IR spectrum evaluate phase purity and crystallinity?\nR-4: “nitrogen radicals may occur during the light-induced electron transfer 200 process”. Why do authors rule out radical formed due to Ct interactions?\nR-5: “Furthermore, high-resolution mass spectrometry detects the formation of a nitro-containing intermediate during UV irradiation”. ?\nR-6: “These experimental results confirm the light-induced structural transformation of the 3Abf-Ofn compounds to Bfd photoproduct, which involves redox interactions with molecular oxygen.” ?\nR-7: I had been tried to read the manuscript very carefully to understand this: “This transformation results in the release of guest 285 Ofn molecules from the lattice,”, however I am not able to. Authors need to reconsider the writing of whole manuscript to make it lucid and self explanatory.\nR-8: Is the co-crystal 3Abf-Ofc reproducible with disordered 3Abc? What causes disorder of 3-Abc? Is the disordered co-crystals obtained by changing the solvents? These questions need to be enquired to rule out the probabilistic nature of co-crystal formation, as authors themselves call it metastable phase. Authors further claim that close proximity and disordered nature of 3Abf leads to its condensation, if the results can not reproduced with other systems with control, the manuscript then losses larger impact and relevance.\nR-9: Authors claim oxidation condensation of 3Abf within the crystal on exposure to hv, what is the oxidant within crystal lattice? Authors also claim relase of Ofn, where does it go?\nR-10 “This behavior may be attributed to the aggregation of molecules within the polymer matrix upon UV irradiation, triggering AIEE, which facilitates radiative transition processes.” How is that possible?\nR-11: “fluorescence lifetime also decreases from 3.93 ns to 4.00 ns” =?\nR-12: “forming a first-level fluorescence-based anti-counterfeiting mark” I doubt it is true.\nDiscussion:\nIt looks like conclusion, instead of discussion. No broader explanation and structure-property correlations are established."}, "author_response": "Response to Reviewers’ Comments\n(Blue italic: Reviewers’ remarks; Black: Our response; Red: revised manuscript)\nResponse to the Comments from Reviewer #1:\nThe manuscript reports the design and characterization of an organic co-crystal system\n(3Abf-Ofn) exhibiting both dynamic photosalient and static photochromic behaviors,\nalong with light-induced fluorescence modulation when embedded into a PMMA matrix.\nThe authors claim to have revealed a new light-driven structural transformation\nmechanism involving guest molecule release and diazetidine formation, which could\ncontribute to multifunctional luminescent material design. The topic is interesting and\npotentially significant to the field of light-responsive organic materials. However,\nseveral critical scientific and presentation issues must be addressed before the\nmanuscript can be considered for publication in Nature Communications.\nAuthors’ response: We sincerely appreciate your positive evaluation and insightful\ncomments on our work. We have carefully revised the manuscript and provided the\npoint-by-point response below.\n1. Figure 1 fails to show how the crystal packing change correlates with\nphotochromism and light-induced cracking. The schematic should illustrate the\nstructure–function relationship and the fate of Ofn molecules after UV irradiation. The\nmechanism for fluorescence quenching under UV light also needs clarification？\nAuthors’ response: Thank you very much for the constructive question. The Figure 1\nhas been further revised in the manuscript.\nBased on density functional theory (DFT) calculations, the highest occupied molecular\norbitals (HOMOs) of 3Abf-Ofn crystals are mainly distributed to electron-donor 3Abf\nmolecule, whereas the lowest unoccupied molecular orbitals (LUMOs) are localized at\nthe electron-acceptor Ofn molecule, suggesting the photoinduced electron transfer from\n3Abf to Ofn. Additionally, the EPR spectroscopy reveals a distinct signal at g = 2.004\nafter UV irradiation, which is absent before irradiation, providing direct evidence for\nthe formation of free radicals during UV irradiation. Notably, the fluorescence lifetime\ndecreased significantly from 4.80 ns to 3.78 ns upon irradiation, indicating an enhanced\nrate of nonradiative transitions. Together with calculation and experimental results, the\nexcited-state energy is funneled into a nonemissive radical state through photoinduced\nelectron transfer, followed by efficient nonradiative dissipation (Angew. Chem. Int. Ed.\n2025, 64, e202422856; J. Am. Chem. Soc. 2020, 142, 5, 2682–2689). On the other hand,\nUV/vis absorption spectroscopy analysis show that the absorption bands of\nphotoproducts during irradiation significantly overlapped with the fluorescence\nemission spectrum of the pristine 3Abf-Ofn material. This indicates a strong\nself-absorption effect, which further weakens the intensity of the fluorescence emission\n(Nat. Commun. 2024, 15, 5519).\nTherefore, the fluorescence quenching can be ascribed to photoinduced electron transfer\ngenerating a nonemissive radical state and the self-absorption effect, which is observed\nfor many organic photochromic compounds (Sci. China Chem. 2021, 64, 1297–1301;\nAngew. Chem. Int. Ed. 2022, 61, e202114100). The fluorescence quenching of\n3Abf-Ofn film can be attributed to the same mechanism.\nPage 8, Line 211-219, three sentences have been adjusted: “Furthermore, 3Abf-Ofn\npowder exhibits a distinct decrease in fluorescence intensity upon UV irradiation (Fig.\n3d, and 3e), consistent with their decreasing trends in both fluorescence lifetimes from\n4.80 to 3.78 ns (Fig. 3f, and 3g) and fluorescence quantum yield (PLQY)\n(Supplementary Figs.13 and 14). The quenching is attributed to the PET generating a\nnon-emissive radical state51, as well as the self-absorption effect52. This is further\nsupported by the notable spectral overlap between the UV/Vis absorption bands of\nphotoproducts during irradiation and fluorescence emission spectra of the pristine\n3Abf-Ofn material.”\n51. Xu, X. et al. Rapidly Generated, Ultra-Stable, and Switchable Photoinduced\nRadicals: A Solid-State Photochromic Paradigm for Reusable Paper Light-Writing.\nAngew. Chem. Int. Ed. 64, e202422856 (2025).\n52. Nie, F. et al. Zero-dimensional halide hybrid bulk glass exhibiting reversible\nphotochromic ultralong phosphorescence. Nat Commun. 15, 5519 (2024).\nFig. 1 | Schematic illustration of 3Abf-Ofn cocrystal and 3Abf-Ofn@PMMA film. a Chemical structures and\nself-assembled patterns of 3-aminodibenzofuran (3Abf), Octafluoronaphthalene (Ofn), 3Abf-Ofn cocrystal and photoproduct\nbis(benzofuran-3-yl) azo (Bfa). b Dynamically tunable fluorescence of 3Abf-Ofn@PMMA film.\n2. Please clarify whether the color change arises from radicals generated by the\nreactant or the photoproduct. Supporting evidence such as EPR spectra would help.\nAuthors’ response: We sincerely thank you for your feedback, which would help to\nimprove the quality of our manuscript. Upon UV irradiation, the sample exhibited a\ndistinct color change, characteristic of a photochromic behavior. To investigate the\nunderlying mechanism, the UV/Vis absorption spectra and electron paramagnetic\nresonance (EPR) spectra are measured. As shown in figure R1, following the UV\nirradiation for 600 s, a new absorption band emerged in the scope of 370-450nm for\n3Abf-Ofn, indicating the formation of light-induced species with radical character.\nFurthermore, a pronounced EPR signal can be detected for the colored 3Abf-Ofn\nsample after irradiation, while only a weak signal was observed before irradiation\n(Figure 3c), confirming the radicals generated of 3Abf-Ofn under UV stimulation for\nvisible coloring process, which is consistent with EPR signals of 1Abf-Ofn (Figure R2)\nand 3Abf-Ofn@PMMA (Figure R3) photochromic materials.\nPage 8, Line 204-211, two sentences have been rephrased: “accompanied by the\nemergence of new absorption band in the scope of 370-450 nm (Supplementary Fig. 12),\nindicating the formation of light-induced species with radical character.\nCorrespondingly, a pronounced signal with g=2.004 can be detected for the colored\nsample after irradiation in electron paramagnetic resonance (EPR) spectra (Fig. 3c),\nwhile only a weak signal is observed before irradiation, verifying the generation of free\nradicals during the light-induced electron transfer process for visible coloring process.”\nFigure R1. UV/Vis spectra of 3Abf-Ofn at different UV irradiation time.\nFigure R2. EPR spectra of 1Abf-Ofn sample before and after UV irradiation.\nFigure R3. EPR spectra of 3Abf-Ofn@PMMA before and after UV irradiation.\nFigure R1, Figure R2 and Figure R3 have been added into Supporting Information as\nFigure S12, Figure S35, and Figure S54, respectively.\n3. The fluorescence enhancement and quenching are attributed to AIEE, but no data\nprove that 3Abf-Ofn exhibits AIE. Provide solution/solid-state experiments or discuss\nwhether the PMMA acts as a barrier to molecular relaxation.\nAuthors’ response: Thank you so much for your kind and pertinent suggestions. As\nwith your suggestions, we have added AIE experiments for 3Abf-Ofn, we are confident\nthese additions will significantly improve the quality of our work.\nAs shown in Figure R4, the fluorescence intensity of 3Abf-Ofn increases significantly\nupon the water fraction (poor solvent) rises from 0% to 80%, respectively. When the\nwater concentration reaches 80%, the fluorescence intensity peaks reach the maximum\nvalues, which is higher than that in pure methanol solution. This can be attributed to the\nformation of molecular aggregation in mixed solution, demonstrating their typical\naggregation-induced emission (AIE) properties.\nUpon further consideration, we recognize that the observed fluorescence enhancement\nin the 3Abf–Ofn@PMMA film does not originate from a conventional AIE mechanism,\nbut rather from a light-triggered aggregation process. In the initial film state, 3Abf-Ofn\nis dispersed within the PMMA matrix, where intramolecular rotation or vibration\nremains unrestrained, resulting in weak fluorescence. Upon initial UV irradiation, local\ndynamic mobility of PMMA chains promotes ordered aggregation (Adv. Funct. Mater.\n2024, 34, 2411584; Chem. Rev. 2018, 118, 5871-5911). Additionally, the constrained\nenvironment of PMMA network acts as a physical barrier, restricting excessive motion\nof aggregated 3Abf-Ofn, achieving photoactivated fluorescence enhancement of\n3Abf-Ofn@PMMA. To confirm this mechanism, we also conducted experiments using\ndifferent polymer matrices (PLA, PS, PVP, and PVA). Films cast from dichloromethane\nsolutions (PLA, PS, PMMA) all shown photoactivated fluorescence enhancement,\nwhereas those prepared from aqueous solutions (PVP, and PVA) did not. This\ndifference is attributed to the strong hydrogen-bonding networks in PVP/PVA matrices,\nwhich impede both the dispersion of cocrystals and the light-induced molecular\nrearrangement required for aggregation. Thus, PMMA acts not only as a barrier to\nmolecular relaxation but also synergistically promotes structural ordering under light\nstimulation.\nPage 15, Line 399-402, one sentence has been added: “This behavior can be\nattributed to the intrinsic aggregation-induced emission (AIE) of 3Abf-Ofn\n(Supplementary Fig. 51) and UV-induced transient polymer chain mobility, facilitating\nmolecular ordered aggregates collectively61-63,6.”\nFigure R4. PL spectra of 3Abf-Ofn in CH OH/H O mixtures with different water fractions (fw).\n3 2\nFigure R4 has been added into Supporting Information as Figure S51.\n4. Explain the mechanism of color recovery upon heating. Structural or spectroscopic\nevidence of the phase transition is needed.\nAuthors’ response: Thank you very much for your constructive feedback. Based on\nyour valuable suggestion, the fact of color recovery upon heating has been further\nstudied and clarified.\nFor 3Abf-Ofn samples irradiated for a short duration followed by heating to 95°C, the\ncolor nearly recovers the original color (Figure R5). Thermogravimetric analysis reveals\nthat the decomposition temperature is approximately 145.8°C, thus excluding thermal\ndecomposition as a contributing factor during the fading process. In addition, powder\nX-ray diffraction (PXRD) results show diffraction patterns highly match those of the\npristine cocrystal (Figure R6), and the infrared spectral signals are also identical to\nthose before irradiation (Figure R7), indicating that no significant structural damage\noccurs during this process. Importantly, the irradiated sample exhibits a strong EPR\nsignal (Figure R8), while pronounced decrease in radical signal intensity after heat\ntreatment, suggesting the photogenerated radicals can be quenched, which is directly\ncorrelated with color fading phenomenon (Angew. Chem. Int. Ed. 2025, 64,\ne202422856).\nHowever, it should be noted that thermal treatment fails to fully restore the sample to its\npre-irradiation state after prolonged UV irradiation, (Figure R9). We observed that new\ncharacteristic diffraction peaks corresponding to the characteristic peaks of azobenzene\nproducts appear in the PXRD patterns (Figure R10). Meanwhile, the intensity of\nUV/Vis absorption peaks significantly decreases upon heating, tending toward initial\nspectral profiles prior to irradiation (Figure R11), indicating the coexistence of the\nreversible radical-based original reactants and azobenzene photoproducts in a mixed\nphase.\nThank you again for kindly reminding us to clarify this point.\nFigure R5. Photographs of reversible photochromic behavior for 3Abf-Ofn powder under irradiated\nfor 20 s.\nFigure R6. PXRD patterns of reversible photochromic behavior for 3Abf-Ofn powder under irradiated\nfor 20 s.\nFigure R7. IR patterns of reversible photochromic behavior for 3Abf-Ofn powder under irradiated for\n20 s.\nFigure R8. ESR spectra of 3Abf-Ofn samples after heating and re-irradiation.\nFigure R9. Photographs of irreversible photochromism for 3Abf-Ofn powder under irradiated for\n1min.\nFigure R10. PXRD patterns of irreversible photochromism for 3Abf-Ofn powder under irradiated for\n1 min.\nFigure R11. UV/Vis spectra of 3Abf-Ofn at different heating time.\nPage 8 and 9, Line 219-240, seven sentences have been added: “Furthermore, the\nyellow powder by short-term UV irradiation can be restored to the initial state upon\nheated to 95°C (Supplementary Fig. 15). The thermal decomposition as a contributing\nfactor during the fading process can be excluded based on decomposition temperature\nof 3Abf-Ofn. Moreover, the PXRD and FT-IR spectra after thermal treatment are nearly\nin agreement with those before photochromic process (Supplementary Figs. 16-17),\nindicating no significant structural changes during this process. Importantly, the\npronounced decrease in EPR signal intensity after heat treatment, suggesting the\nphotogenerated radicals can be quenched, which is directly correlated with the color\nfading behavior51,53. Furthermore, repeated UV irradiation of the thermally treated\n3Abf-Ofn samples leads to the reappearance of the EPR signal and a darkening of the\nsample color (Supplementary Fig. 18), confirming the color recovery is primarily\nattributed to the regeneration of photogenerated radicals upon irradiation. However,\nfollowing prolonged UV irradiation, the powder undergoes a color darkening upon\nthermal treatment (Supplementary Fig. 19) and exhibits new diffraction peaks in the\nPXRD patterns (Supplementary Fig. 20), owing to the active radicals may trigger side\nreactions54. Meanwhile, the intensity of UV/Vis absorption peaks significantly\ndecreases upon heating, tending toward initial spectral profiles prior to irradiation\n(Supplementary Fig. 21), indicating the coexistence of the reversible radical-based\noriginal reactants and photoproducts in a mixed phase.”\nFigure R5-R11 have been added into Supporting Information as Figure S15-Figure 21.\n5.Clarify the reason for in 3Abf-Ofn@PMMA and its absence in 3Abf-Tpn@PMMA.\nDefine “Tpn” and explain why changing the polymer matrix removes EWDE.\nAuthors’ response: We thank you for raising this important concern. Excitation\nwavelength dependent (EWDE) materials are a kind of smart materials whose luminous\ncolors can be varied in response to the excitation energy. Here we did not observe such\nshifts in the emission spectra when exciting bulk macroscopic 3Abf-Ofn cocrystals at\ndifferent excitation wavelengths. In contrast, upon addition of PMMA matrix, the\n3Abf-Ofn@PMMA can be seen the obviously EWDE behavior, indicating the presence\nof multiple emissive species in aggregation states. It could be attributed to the fact that\nthe polymer matrix can contribute many O-containing functional groups around the\n3Abf-Ofn molecules, introducing new energy-level structures for electronic transition\nunder various excitation wavelengths (J. Am. Chem. Soc. 2017, 139, 15088-15093;\nSmall 2017, 1702098). Indeed, XPS spectra also verifies the presence of C-O functional\ngroups. Moreover, PMMA provides rigid environment and specific surface interaction\nwith the emitter, which could potentially immobilize aggregation states. The findings\nare in line with studies available in the literature that the emission position is related to\nsurface functional group modification (Adv. Mater. 2015, 27, 1663; Nanoscale 2015, 7,\n7927). In support of these points, we choose PVA as the polymer matrix with other\nfunctional groups. The O1s spectrum of 3Abf-Ofn@PVA shows two peaks at 533.38,\nand 532.35 eV, which are assigned to C-O-C and C-O-H (Figure R12). While the strong\nhydrogen bonding capability may restrict molecular flexibility and promote fewer\nemissive state, leading to reduced spectral tunability of the EWDE behaviors, further\nconfirming that the introduction of different hydrogen bonding interactions that gives\nrise to different aggregation structures and emission states in local microenvironment.\nNotably, the different EWDE behaviors can be observed by varying the luminescent\ndopants embedded within the same PMMA matrix. This diversity may be related to\nintrinsic molecular properties. For instance, 3Abf-Tcpn@PMMA are absent of EWDE,\nattributing to 3Abf-Tcpn inherently weak fluorescence with a measured PLQY of only\n0.74% (Figure R13), because the presence of Cl atoms enhances spin-orbit coupling,\npromoting rapid intersystem crossing (ISC) from the singlet to the triplet state and\neffectively suppressing fluorescence emission (Nat. Commun. 2024, 15, 5519). Even\nwhen doped into the polymer matrix, the emission signal of 3Abf-Tpn@PMMA is\nnearly undetectable under optimal excitation conditions, and PLQY at a negligible level\nwith 0.02% (Figure R14), preventing the observation of EWDE behavior. Likewise, the\nPLQY for 3Abf-Tcpn@PVA is only 0.08% (Figure R15). Thus, these results\ndemonstrate that the EWDE behavior is not only determined by the microenvironment\nprovided by polymer matrix, but also arises from the synergistic effect between the\nmatrix confinement and the intrinsic structural characteristics of the luminescent\nmaterial.\nFor greater accuracy and standardization, we have redefined the abbreviation for\n3,4,5,6-Tetrachlorophthalonitrile from the original \"Tpn\" to \"Tcpn\", and have revised\nall mentions of \"Tpn\" to \"Tcpn\" throughout the manuscript.\nFigure R12. (a) XPS of 3Abf-Ofn@PVA. High-resolution XPS spectra of C 1s (b), O 1s (c), and N 1s\n(d) respectively.\nFigure R13. PLQY of 3Abf-Tcpn before UV light irradiation.\nFigure R14. PLQY of 3Abf-Tcpn@PMMA before UV light irradiation.\nFigure R15. PLQY of 3Abf-Tcpn@PVA before UV light irradiation.\nPage 15, Line 422-427, two sentences have been added: “In contrast, neither\nsignificant fluorescence enhancement nor EWDE is detected in 3Abf-Tcpn@PMMA\nand 3Abf@PMMA film, and the overall fluorescence intensity is weak, respectively\n(Supplementary Figs. 64-66). Supplementary Figs. 67-69 clearly indicate that the\nphotoresponse properties of films are related to the inherent optical properties of the\ndopant molecules themselves.”\nPage 15, Line 431-434, two sentences have been added: “XPS spectra of\n3Abf-Ofn@PVA show the presence of C-O-C and C-O-H bonding signals at 533.38,\nand 532.35 eV, respectively (Supplementary Fig. 75). The strong bonding interactions\nrestrict molecular flexibility and promote fewer emissive state.”\nFigure R13, Figure R14, and Figure R12 have been added into Supporting Information\nas Figure S67, Figure S68, and Figure S75.\nAlso, check whether the fluorescence enhancement–quenching process persists with\nother matrices.\nAuthors’ response: Thank you for the insightful and valuable suggestion. To\ninvestigate the influence of polymer matrices on fluorescence enhancement-quenching\nprocess, 4 wt.% 3Abf-Ofn was doped into polylactic acid (PLA), polyacrylamide (PA)\nand polyvinylpyrrolidone (PVP) films using dichloromethane as the solvent,\nrespectively. Upon UV irradiation, 3Abf–Ofn@PLA, 3Abf–Ofn@PA, and\n3Abf–Ofn@PVP exhibited that similar light-regulated fluorescence enhancement and\nquenching behaviors (Figure R16-R18), indicating that the photoactivated aggregation\ninduced luminescence have excellent reproducibility in various hydrophobic polymer\nmatrices.\nFigure R16. Emission spectra mapping at different irradiation time of 3Abf-Ofn@PLA film.\nFigure R17. Emission spectra mapping at different irradiation time of 3Abf-Ofn@PA film.\nFigure R18. Emission spectra mapping at different irradiation time of 3Abf-Ofn@PVP film.\nTable R1. Fluorescence enhancement–quenching process in other matrices\nPolymer matrices Fluorescence enhancement-quenching process\nPMMA (dichloromethane) YES\nPVA (water) NO\nPLA (dichloromethane) YES\nPA (dichloromethane) YES\nPVP (dichloromethane) YES\nPage 15, Line 422-427, two sentences have been added: “Furthermore, we further\nfabricated 3Abf-Ofn doped films using other polymer matrices, including polylactic\nacid (PLA), polyamide (PA), and polyvinylpyrrolidone (PVP) in dichloromethane. The\nresults reveal that similar light-regulating behavior (Supplementary Figs. 76-80) to that\nin 3Abf–Ofn@PMMA film, demonstrating that the photoactivated aggregation induced\nluminescence mechanism exhibits excellent reproducibility in various hydrophobic\npolymer matrices.”\nFigure R16-R18 have been added into Supporting Information as Figure S76-S78.\n6. “Fluorescence lifetime decreases from 3.93 ns to 4.00 ns” is incorrect. Please revise.\nAuthors’ response: Many thanks for your reminder and sorry for the mistake. The\nsentence has been modified: “Fluorescence lifetime slightly increases from 3.93 ns to\n4.00 ns” in Page 14, Line 400.\n7. Figure 3: Crystal images unclear—provide higher-resolution photos.\nAuthors’ response: Thank you for your reminding. We replaced crystal images of\nFigure 3a with a clear picture in the manuscript.\nFig. 3 | Photosalient effects and photochromism of 3Abf-Ofn. a The photographs of light-induced cracking and popping\nprocesses for 3Abf-Ofn crystal. b The photochromic behavior of 3Abf-Ofn powder. c EPR spectra of 3Abf-Ofn before and\nafter UV irradiation. d Emission spectra and emission spectra mapping (e) at different irradiation time of 3Abf-Ofn. f\nFluorescence lifetime decay profiles of 3Abf-Ofn before UV light irradiation. g Fluorescence lifetime decay profiles of\n3Abf-Ofn after UV light irradiation.\n8. Figure 22: Enlarge key NMR peaks to better show new product formation.\nAuthors’ response: Thank you for kindly reminding us, the key NMR peaks in the\nmanuscript have been enlarged for enhanced visibility.\nFigure S27. 1H NMR spectra of 3Abf-Ofn before (a) and after (b) UV irradiation in DMSO-d6.\n9. Figures S15–S16: Use separate real images for heating/pressure recovery, not\nidentical ones.\nAuthors’ response: We sincerely thank the reviewer for the careful reading and\nvaluable suggestion. we have replaced the previously photochromic photographs with\ndistinct real images corresponding to external stimuli, respectively.\nFigure S15. Reversible photochromic behavior of 3Abf-Ofn under heating.\nFigure S23. Photograph of reversible fluorescence of 3Abf-Ofn after prolonged irradiation followed\nby grinding.\n10. References: Add key missing works -Adv. Mater. 2025, 37, 2504417; Angew. Chem.\nInt. Ed. 2025, e202506549; Chem. Soc. Rev. 2024, 53, 10312.\nAuthors’ response: Thank you for your helpful suggestions. We add the references\ninto the manuscript as\n35. Ren, S. et al. A Relay-Type Solid-State Macrocyclic Host–Guest System for\nSelective Isomer Adsorption, Controlled Release, and Turn-On Colorimetric Sensing of\n1-/2-Bromoalkanes. Adv. Mater. 37, 2504417 (2025).\n41. Ren, S. et al. Geminiarene-Based Charge-Transfer Cocrystals with Dichromatic\nVariants and Stimuli-Responsive Structural Interconversion. Angew. Chem. Int. Ed. 64,\ne202506549 (2025).\n37. Ren, S., Qiao, G.-Y., Wu, J.-R. Supramolecular-macrocycle-based functional\norganic cocrystals. Chem. Soc. Rev. 53, 10312-10334 (2024).\nWe hope our responses have fully addressed your concerns.\nReviewer #2:\nIn this study, the authors constructed an organic cocrystal that exhibits both dynamic\nmotions and photochromic properties. The crystal was further integrated into a polymer\nfilm to demonstrate information encryption technology based on its photochromic\nbehavior. Although the dynamic response relies on an unconventional coupling reaction,\nthe study lacks an in-depth investigation into the mechanism of this new reaction. The\nnovelty of this work is not immediately apparent, as the integration of mechanical\ndynamic motion, photochromism, and photoluminescence changes has been commonly\nobserved. (ACS Appl. Mater. Interfaces 2020, 12, 14, 16856–16863. J. Mater. Chem. C,\n2023,11, Adv. Funct. Mater. 2023, 33, 2212886. J. Am. Chem. Soc. 2023, 145, 45,\n24636–24647. Chem. Soc. Rev., 2024,53, 6636-6653. 4375-4383. J. Am. Chem. Soc.\n2024, 146, 47, 32757–32765. Latest Article: Stiffening Organic Crystals through\nPolymerization Using Visible Light) Furthermore, the mechanism explanations are\nneither rigorous nor sufficient. The current report lacks significant, unique findings,\nnovel insights, or the fundamental advances required for publication in Nature\nCommunications.\nAuthors’ response: Thank you for your positive comments. We understand your\nconcerns regarding the novelty and mechanism aspects of this study. In response, we\nhave conducted additional experiments and computational analyses to provide a more\nrigorous and comprehensive explanation of the mechanism in revised manuscript. We\nhope that the revisions and improvements would satisfactorily address your concerns.\nPage 11 and 12, Line 306-334, one paragraph has been added: “To elucidate the\nreaction pathway from 3Abf-Ofn to Bfa, the control experiments with alternative\nelectron donors (1-aminodibenzofuran (1Abf) and 2-aminodibenzofuran (2Abf)) and\nacceptors (1,2,4,5-Tetracyanobenzene (Tcnb), 3,4,5,6-Tetrafluorophthalonitrile (Tfpn),\nand 3,4,5,6-Tetrachlorophthalonitrile (Tcpn)) under identical conditions are conducted.\nBfa compounds can be detected (m/z 363.111) by HRMS upon UV irradiation of\n1Abf–Ofn (Supplementary Fig. 33) and 2Abf–Ofn (Supplementary Fig. 34), which\ndemonstrate that the strategy can be extended to more systems. EPR results of\n1Abf–Ofn and 2Abf–Ofn reveal the presence of radical signals by PET, accompanied\nby photochromic behaviors (Supplementary Figs. 35–37). Notably, the reaction\nproceeds efficiently even under a nitrogen atmosphere, as evidenced by both Bfa\nproduct formation (Supplementary Fig. 38) and photochromic behavior (Supplementary\nFig. 39), confirming that this reaction is not a conventional oxidative coupling pathway\nwith molecular oxygen58,59. However, it is failed to observe color changes and yield\nazo compounds in 3Abf-Tcnb, 3Abf-Tfpn and 3Abf-Tcpn (Supplementary Fig. 40),\nunderscoring the crucial role of Ofn in driving the reaction. Based on the experimental\nfindings, we propose the reaction mechanism. Upon UV irradiation, photoinduced\nelectron transfer from the electron-donor 3Abf to the electron-acceptor Ofn generates\nradicals, which subsequently undergo intermolecular N–N coupling to form the\nazobenzene derivative Bfa. Density functional theory (DFT) calculations (Fig. 4f) are\nperformed to support our proposed reaction pathway. Upon photoexcitation, 3Abf-Ofn\nenters the singlet excited state, followed by intermolecular electron transfer to generate\nradical species. Subsequent the -NH₂•+ of 3Abf deprotonates to form -NH•, resulting in\na reduction of the system energy to 0.89 kcal/mol. The generated radical then\nparticipates in N–N coupling process to yield an azo-linked dimer, and final product\nenergy (1.43 kcal/mol) is lower than the initial state, demonstrating that PET-assisted\ncoupling reaction of 3Abf-Ofn is thermodynamically favorable.”\nFigure S33. High-resolution mass spectra of 1Abf-Ofn after UV irradiation.\nFigure S34. High-resolution mass spectra of 2Abf-Ofn after UV irradiation.\nFigure S35. EPR spectra of 1Abf-Ofn before and after UV irradiation.\nFigure S36. EPR spectra of 2Abf-Ofn before and after UV irradiation.\nFigure S37. Photochromic behaviors of 1Abf-Ofn and 2Abf-Ofn powder.\nFigure S38. High-resolution mass spectrum of 3Abf-Ofn under a nitrogen atmosphere.\nFigure S39. Photochromic behaviors of 3Abf-Ofn under a nitrogen atmosphere.\nFigure S40. Photographs of 3Abf-Tcnb, 3Abf-Tfpn, and 3Abf-Tcpn powder before and after\nirradiation.\nFig. 4f. Energy profile of the reaction by DFT calculations.\nOur point-to-point responses are as follows：\nMajor issues:\n1. In page 4, line 114. Miller indices are referenced; authors are advised to specify the\nsimulation methods used. Furthermore, it is recommended to use a single-crystal X-ray\ndiffraction for more accurate determination of the Miller indices, which is crucial for\nrevealing the reaction mechanism and mechanical behavior.\nAuthors’ response: We sincerely thank the reviewer for this valuable suggestion. We\nhave added the simulation methods of 3Abf-Ofn in the revised Methods section.\nThe Miller indices were performed based on single crystal XRD data. The crystal\nstructure of the 3Abf–Ofn cocrystal is solved and refined (CCDC No. 2479066),\nproviding precise unit cell parameters and space group symmetry. Using single crystal\nstructural model of 3Abf-Ofn, the growth crystal morphology modelling and\ncorresponding Miller indices of dominant faces are predicted through the\nBravais–Friedel Donnay–Hulme (BFDH) method in the Mercury software1,2. The\npredicted morphology shows that the largest crystal faces correspond to the (002) miller\nplane, which is parallel to the slipped 3Abf–Ofn columnar stacks (Figure R19).\nPhotomechanical response behavior occurs perpendicular to this plane.\nPage 5, Line 123-127, two sentences have been added: “which are consistent with the\npredicted crystal morphology by Bravais−Friedel Donnay−Harker calculations44,45 (Fig.\n2a). The predicted morphology shows that the largest crystal faces correspond to the\n(002) miller plane based on the single-crystal structure analysis, which is parallel to the\nslipped 3Abf–Ofn columnar stacks (Fig. 2b).”\nCharacterizations in the revised manuscript: Crystal morphology modelling and\ncorresponding Miller indices of dominant faces are predicted through the\nBravais–Friedel Donnay–Hulme (BFDH) method in the Mercury software based on\nsingle crystal XRD data.\nFigure R19. (a) Crystal morphology and corresponding Miller indices of 3Abf–Ofn. (b) The packing\nstructure along the (002) Miller plane.\nWe add the references into the supporting information as\n44. Ye, X. et al. 1D versus 2D cocrystals growth via microspacing in-air sublimation.\nNat. Commun. 10, 761 (2019).\n45. Zhao, Z. et al. Photochromic luminescence of organic crystals arising from subtle\nmolecular rearrangement. Nat. Commun. 15, 5054 (2024).\nFigure R19 above has been added in revised manuscript as Figure 2a and Figure 2b.\n2. The portion regarding the crystal's fluorescence response to acid stimulation does\nnot significantly contribute to the main focus of the article, as it appears to digress from\nthe central theme. Therefore, I recommend removing this section.\nAuthors’ response: We sincerely thank the reviewer for this thoughtful suggestion. To\nensure greater consistency with the main content of the manuscript, we have deleted the\nsection discussing acid stimulation.\n3. In page 5, line 139, it is recommended that the TGA data of the 3Abf and Ofn be\nincluded as well.\nAuthors’ response: We thank the reviewer for this suggestion. As suggested, the TGA\ndate of the 3Abf and Ofn have added in the revised supplementary information, as\nshown in Figure R20 below.\nPage 6, Line 155-159, one sentence has been added: “which differs from thermal\nbehavior that of the individual 3Abf and Ofn molecules (Supplementary Fig. 6),\nfurther confirming two-component self-assembly strategy can effectively modulate the\nthermal stability of single-component systems.”\nFigure R20. TGA curves of pure 3Abf (a) and Ofn (b), respectively.\nFigure R20 above has been added into Supporting Information as Figure S6.\n4. In page 6, line 163-165, through microscopic observation, it is insufficient to\nvisually conclude that the crystal exhibits no thermal response behavior. It is\nrecommended to perform DSC testing to provide supplementary evidence.\nAuthors’ response: We thank the reviewer for raising this important question. Based\non the reviewer’s professional comment, DSC testing was conducted to further verify\nthat the 3Abf-Ofn crystals have no thermal response behavior. As shown in Figure R21,\nDSC result shows that a melting point of 139 °C for the as-prepared 3Abf-Ofn crystals,\nwhich is higher than the temperature at which light-responsive behavior occurs under\nUV irradiation, indicating that its mechanical motion and photochromic behavior are\ndriven by light-responsive properties rather than thermal effects.\nFigure R21. The DSC curve of 3Abf-Ofn.\nPage 7, line 189-195, three sentences have been revised: “Crucially, thermal effects\ncan be excluded as the primary driver of these responses. Differential scanning\ncalorimetry (DSC) result (Supplementary Fig. 10) indicates that the as-prepared\n3Abf-Ofn crystals have a melting point of 139°C, and no morphological changes are\nobserved when the crystals are heated below this temperature (Supplementary Fig. 11).\nMore importantly, the maximum temperature of the crystals reached about 42 °C under\ncontinuous UV irradiation.”\nFigure R21 above has been added into Supporting Information as Figure S10.\n5. In page 7, line 186-188, The powdered sample loses its macroscopic mechanical\nresponse, primarily because such mechanical behavior is governed by a size effect-the\nsmall dimensions prevent the accumulation of sufficiently large strain to drive crystal\ndeformation and fragmentation. The term \"aggregates\" mentioned here may easily lead\nto ambiguity; could it refer to changes in the packing structure? Reference: Chem. Rev.\n2015, 115, 22, 12440–12490.\nAuthors’ response: We sincerely thank the reviewer for this insightful and important\ncomment. The reviewer is correct that the term “aggregates” can be ambiguous, as it\ncould be interpreted as referring to molecular assemblies (e.g., H- or J-aggregates in\nsolution or thin films) rather than to the physical state of the solid sample, particularly\nin the context of solid-state luminescent materials. Furthermore, the fine particles limit\nthe accumulation of energy and therefore prevent the release of critical stress required\nfor mechanical response. As emphasized in the cited review (Chem. Rev. 2015, 115, 22,\n12440–12490), macroscopic mechanical effect of crystal is a dynamic process, which is\nclosely related to size effect. The \"aggregates\" was used to describe the ground powder\ncomposed of micron-sized crystalline fragments in our original manuscript; the packing\nstructure has not undergone structural changes for ground powder. we apologize for our\nincomplete consideration and have replaced the term “aggregates” with “size effect.”\nPage 7, line 201, one sentence has been revised: “confirming that the fine particles\nprevent the accumulation of energy due to size effect50.”\n50. Naumov, P. et al. Mechanically Responsive Molecular Crystals. Chem. Rev. 115,\n12440–12490 (2015).\n6. In page 7, line 201-206, the reversible process of heating- or mechanical\nstress-induced fluorescence recovery needs to be demonstrated. This process may be\nmore complex than initially assumed, as it may involve double-bond cleavage and\neutectic reassembly rather than a simple mechanism.\nAuthors’ response: We sincerely thank the reviewer for bringing this to our attention.\nBased on the reviewer’s insightful comments, we agree that the reversible process is\nmore complex and take the opportunity to clarify it with experimental evidence.\nThe observed fluorescence recovery phenomenon after heating or grinding originates\nfrom the destruction of non-fluorescent species generated under UV irradiation, as\nconfirmed by EPR characterization of photogenerated radicals. Specifically, the PXRD\n(Figure R22) and FT-IR spectra (Figure R23) after thermal treatment are nearly in\nagreement with those before irradiation, indicating no significant structural changes\nduring this process. The pronounced decrease in EPR signal intensity (Figure R24) after\nheat treatment, attributing to the quenching of photogenerated radicals, which directly\ndemonstrates that optical recovery is primarily governed by thermal quenching of\nphotogenerated free radicals, consistent with reported mechanisms for radical-type\nphotochromic materials in the literature (Angew. Chem. Int. Ed. 2025, 64, e202422856).\nMoreover, UV/Vis absorption peaks blue-shift toward their initial positions (Figure\nR25), weakened the self-absorption effect. However, after prolonged irradiation, the\nsample underwent a significant black color change and exhibits new diffraction peaks in\nthe PXRD patterns (Figure R26), owing to the active radicals may trigger side reactions.\nTherefore, the heating-based recovery strategy is considerably limited by poor fatigue\nresistance, likely owing to the formation of multiple mixed phases within irradiation\nsystem. We apologize for not making this point clearer in our initial statement.\nFurthermore, PXRD diffraction peaks of the grinding-induced recovery sample are\nconsistent with those of the light-irradiation sample, with only slight variations in peak\nintensity and no emergence of new diffraction peaks (Figure R27), proving mechanical\nforce neither changes the long-range crystalline structure nor breaks the –N=N– bonds.\nMechanical grinding enables multiple cycles of fluorescence recovery, because it\ninduces only physical disorder without accompanying chemical alteration, preserving\nthe photoreversibility of the system.\nFigure R22. PXRD patterns of 3Abf-Ofn upon heating for short-term UV irradiation.\nFigure R23. FT-IR spectra of 3Abf-Ofn upon heating for short-term UV irradiation.\nFigure R24. EPR spectra of 3Abf-Ofn samples after heating and re-irradiation.\nFigure R25. UV/Vis spectra of 3Abf-Ofn at different heating time.\nFigure R26. PXRD patterns of 3Abf-Ofn after prolonged irradiation (more than 20 s) followed by\nheating.\nFigure R27. PXRD patterns of 3Abf-Ofn after grinding.\nPage 8, line 223-236, four sentences have been revised: “the PXRD and FT-IR\nspectra after thermal treatment are nearly in agreement with those before photochromic\nprocess (Supplementary Figs. 16-17), indicating no significant structural changes during\nthis process. Importantly, the pronounced decrease in EPR signal intensity after heat\ntreatment, suggesting the photogenerated radicals can be quenched, which is directly\ncorrelated with the color fading and fluorescence recovery 51,53. Furthermore, repeated\nUV irradiation of the thermally treated 3Abf-Ofn samples leads to the reappearance of\nthe EPR signal and a darkening of the sample color (Supplementary Fig. 18),\nconfirming the recovery process is primarily attributed to the regeneration of\nphotogenerated radicals upon irradiation. However, following prolonged UV irradiation,\nthe powder undergoes a color darkening upon thermal treatment (Supplementary Fig.\n19) and exhibits new diffraction peaks in the PXRD patterns (Supplementary Fig. 20),\nowing to the active radicals may trigger side reactions54.”\nPage 9, line 240-245, two sentences have been revised: “In contrast, mechanically\ngrinding achieves good cycling stability without altering the crystalline phase, as\nevidenced by PXRD patterns (Supplementary Fig.22) that are consistent with those of\nthe light-irradiation product. This structural recovery is accompanied by a significant\nincrease in bule fluorescence intensity observable to the naked eye (Supplementary Fig.\n23).\nFigure R22-27 above have been added into Supporting Information as Figure S16-18,\nFigure S20-22.\n7. In page 9, line 226-228, the authors mention that they obtained a single crystal after\nthe photoreaction, which allowed single crystal structure was directly carried out by\nsingle crystal Xray. However, the photoresponsive behavior of this crystal is\naccompanied by fragmentation and disintegration. It would be critical to ascertain the\nthree-dimensional size of the single crystal used for the structural analysis, as well as\nthe light power-suitable for such analysis-was acquired.\nAuthors’ response: Thank you for your reminder. We sincerely apologize for the\nunclear description of the single crystal and light power in the original manuscript.\nAt first, the plate-shaped 3Abf-Ofn crystals (0.15×0.1×0.05 mm3) were irradiated\nwith UV light (365 nm, 441 mW cm-2) for 20 s, the freshly splitting crystals debris\nmaintained in relatively high quality for SCXRD experiments. The results reveal show\nsubtle changes in unit cell parameters (Table R2), confirming structural rearrangement\nduring the light photoinduced process. To identify the final photoreaction product, we\nattempt to prolonged UV irradiation to 5 min, but this caused severe crystal\nfragmentation and reduced crystallinity, preventing high-quality diffraction data\ncollection during photosalient effects despite repeated attempts. According to the\nliterature-reported methods for photosensitive materials (J. Am. Chem. Soc. 2022, 144,\n6278−6290; Angew. Chem. Int. Ed. 2007, 46, 8945-8947; J. Am. Chem. Soc. 2025, 147,\n20426–20430; Angew. Chem. Int. Ed. 2017, 129, 9591-9595 Angew. Chem. Int. Ed.\n2020, 59, 22623-22630. Angew. Chem. Int. Ed. 2014, 53, 5907 -5911), the sample was\nirradiated under the same UV source for 2 h until it turned dark brown. The\nphotoproduct was then dissolved in CH₂Cl₂/MeOH (1:1 v/v), then slowly re-crystallized\nto yield single crystals of the pure Bfa, whose structure was unambiguously confirmed\nby SCXRD determination.\nWe have clarified this structural analysis strategy in the revised manuscript and\nprovided full experimental details, such as crystal dimensions, light source\nspecifications, and irradiation time.\nTable R2. Crystallographic data for 3Abf-Ofn cocrystals before and after UV irradiation for 20 s.\n3Abf-Ofn\nCompound\nBefore irradiation After irradiation (20 s)\nFormula C H F NO C H F NO\n22 9 8 22 9 8\nMr 455.3 455.3\nCrystal system Monoclinic Monoclinic\nSpace group P2 /c P2 /c\n1 1\na (Å) 7.4712(7) 7.4715(5)\nb (Å) 6.4050(6) 6.4200(4)\nc (Å) 19.317(2) 19.2517(15)\nα (°) 90 90\nβ (°) 100.467(6) 100.362(7)\nγ (°) 90 90\nPage 7, line 265-270, two sentences have been revised: “However, the crystals quality\nof 3Abf-Ofn has been significantly deteriorated after sufficient irradiation for 2 h,\nmaking it difficult to resolve photochemical reaction products by single-crystal X-ray\ndiffraction. After numerous attempts10,14,55-57, the final photoproduct can be obtained\nsuccessfully through solution recrystallization and confirmed the formation of only\nBfa.”\nPage 6, line 168, the light source specifications has been added: “Upon irradiation\nwith UV light (365 nm, 441 mW/cm2)”\n8. The melting point of Ofn is approximately 80 °C, and the authors also mention that\nthe crystal temperature does not exceed 50°C after illumination. Given such a high\nmelting point, along with the constraints imposed by the lattice and intermolecular\ninteractions, it is puzzling how Ofn can escape while simultaneously yielding\nhigh-quality single crystals of Bfd. Furthermore, according to the ESP calculations of\nBfd, there is a clear electronic complementarity with Ofn, suggesting the presence of\nsignificant electrostatic interactions. So, what mechanism enables Ofn to be released\nfrom the lattice? After Ofn overflowed from the lattice, does it sublimate and leave or\nrecrystallize? That is, in what form does it exist?\nAuthors’ response: Thank you for this excellent and perceptive question, which has\nhelped us clarify a critical aspect of our work. We acknowledge that our original\nmanuscript did not sufficiently clarify the chemical nature of the photoinduced\ntransformations, which led to this understandable confusion.\nIn fact, the photoreaction process is not a simple physical release of Ofn from an\nintact host framework. Instead, it involves an irreversible photochemical reaction of the\n3Abf molecule itself, which fundamentally destabilizes the crystal lattice of 3Abf-Ofn\nand enables Ofn release. Upon UV irradiation in air, 3Abf undergoes coupling to form\nan azo-linked dimeric product. This reaction is a covalent transformation, not a\nconformational change. The newly formed azo-dimer has a significantly different\ngeometry, dipole moment, and volume compared to 3Abf, which destroys the original\npacking motif that is stabilized by weak noncovalent interactions (C–H⋯F, π⋯π) in\nco-crystal. Although ESP maps show strong electronic complementarity in the pristine\n3Abf-Ofn cocrystals, this complementarity is lost immediately upon 3Abf oxidation.\nOfn is no longer stabilized within the lattice and is released due to loss of structural\ncompatibility and the accumulation of internal strain. Consequently, the release\nbehavior of Ofn is caused by photoinduced chemical reaction, not driven by thermal\nmelting.\nFurthermore, no signal attributable to Ofn (m/z 272.09 [M]⁺) can be detected at\nvarious irradiation time in HRMS. XPS analysis reveals a significant weakening in the\nC–F signal, further confirming the loss of F species from the material. On the other\nhand, Ofn, as a derivative of naphthalene, has low melting point (87-88 °C) and high\nvapor pressure, which makes it being easy to sublimate even at room temperature.\nUnder UV irradiation, the local sample temperature rises to approximately 50°C, which\nfurther facilitates Ofn sublimation. This phenomenon is corresponding to “where the\nlow melting point (87‒88 °C) and high vapor pressure of octafluoronaphthalene make it\nvolatilize from the cocrystal with temperature increasing” in Nature Communications,\n2019, 10, 761. Therefore, we speculate that Ofn may have departed via sublimation.\n“High-quality single crystals” referenced in the manuscript are Bfa photoproduct,\nwhich obtained by dissolving the fully irradiated 3Abf-Ofn crystals and re-crystallizing\nfrom solvent.\nPage 13, line 362-366, three sentences have been revised: “Meanwhile, Ofn is no\nlonger stabilized within the lattice due to loss of structural compatibility. Given its low\nmelting point and high vapor pressure60, Ofn readily sublimes even at room temperature,\nthus facilitating its escapes through sublimation as the temperature increases under UV\nirradiation.”\n60. Ye, X., Liu, Y., Guo, Q. et al. 1D versus 2D cocrystals growth via microspacing\nin-air sublimation. Nat Commun. 10, 761 (2019).\n9. Figure S22 is small. Additionally, the figure indicates the use of DMSO-d6 as the\ndeuterated solvent, while the caption states that CDCl3 was used. The proton NMR peaks\nshould be assigned accordingly. Furthermore, the chemical shift at\napproximately 5.5 ppm should correspond to the -NH group, which shows no change\n2\nbefore and after light irradiation—neither a reduction in peak area nor the appearance\nof new peaks. This does not support the occurrence of a chemical reaction.\nFurthermore, the high-resolution mass spectrometry data indicate only trace amounts\nof Bfd, making it difficult to believe that such a minimal amount of reaction product\ncould yield high quality single crystals suitable for X-ray diffraction analysis.\nAuthors’ response: We sincerely thank the reviewer for this insightful observation. In\nresponse, we have corrected the caption to DMSO-d6 in the revised Supporting\nInformation. Additionally, Figure S27 has been enlarged and supplemented with\ndetailed peak assignments to enhance clarity.\nIn the initial experiment, no significant changes are observed in the 1H NMR after 1\nmin of UV irradiation, due to the extremely low conversion rate of the photochemical\nreaction at this stage. To more accurately track the reaction progress, we prolonged the\nirradiation time and re-collected the ¹H NMR spectrum. The results reveal a significant\nchange in the -NH₂ peak at approximately 5.5 ppm (Figure R28), indicating the -NH₂\nhas undergone transformation with extended illumination duration.\nSimilarly, the high-resolution mass spectrometry (HRMS) data indicates only trace\namounts of Bfd after UV irradiation for 1 min, which is used to monitor the early stage\nof the photoreaction (Figure R29a). However, probably because both poor crystal\nquality and the minimal presence of reaction or rearranged molecules in large-sized\ndecomposed micro-/nanocrystals original crystals (Angew. Chem. Int. Ed. 2021, 60,\n5400-5406; Chem.Mater.2024, 36, 8338-8348), making it difficult to resolve\nphotochemical reaction products Bfa by single-crystal X-ray diffraction experiments at\nthis stage. Furthermore, after sufficient illumination for 2 h, the relative abundance of\nBfd molecular ion peak markedly enhanced (Figure R29b), further confirming the\naccumulation of photochemical reaction products over time.\nIt is important to note that our final photoproduct is obtained through solution\nrecrystallization and confirmed the formation of Bfa, not through the direct\nsingle-crystal-to-single-crystal (SCSC) transformation.\nWe sincerely apologize for any potential misunderstanding arising from the original\ndescription and have revised the relevant sections accordingly.\nPage 11, line 288-289, one sentence has been revised: “In addition, the intensity of\nthe peak at 5.5 ppm in 1H NMR spectra exhibit a significant change following UV light\nirradiation, indicating an alteration in the chemical environment of the hydrogen atoms\nof -NH₂ (Supplementary Fig. 27).\nPage 11, line 297-301, two sentences has been revised: “High-resolution mass\nspectrometry (HRMS) further confirms the formation of the final product Bfa\n(C₂₄H₁₄N₂O₂), with a detected m/z value of 363.111 matching the calculated exact mass.\nMoreover, the relative abundance of Bfa markedly increases from 20% to nearly 100%\nupon continuous irradiation for 2 h (Supplementary Fig. 30).”\nFigure R28, and Figure R29 above have been added into Supporting Information as\nFigure S27, and Figure S30.\nFigure R28. 1H NMR spectra of 3Abf-Ofn before and after 365 nm irradiation for 1h (500 MHz,\nDMSO-d6).\nFigure R29. High-resolution mass spectra of 3Abf-Ofn sample after UV irradiation for 60 s (a) and 2h\n(b), respectively.\n10. In page 10, line 270-276, the authors used pristine 3Abf and 3Abf-Tpn as reference\nsystems to elucidate the distinctive mechanical motion of the 3Abf-Ofn cocrystal. It is\nrecommended that the authors explain the origin of the distinct mechanical properties\nexhibited by 3Abf-Ofn from the perspectives of crystal packing and intermolecular\ninteractions.\nAuthors’ response: Thank you for your valuable and thoughtful suggestions, which\nhas significantly enhanced the rigor and transparency of our structural characterization.\nBased on the reviewer’s helpful guidance, we further analyze the distinct mechanical\nproperties of 3Abf–Ofn in terms of crystal packing and intermolecular interactions, and\nsupplied more discussion: in the 3Abf-Ofn cocrystal, 3Abf and Ofn molecules assemble\ninto parallel D-A-D-A columnar stacks. The intermolecular interactions are dominated\nby weak interactions (C–F⋯H, F⋯F and π-π) contacts, lacking strong directional\nhydrogen bond constraints between 3Abf and Ofn. Notably, adjacent columns of\ndisordered 3Abf molecules pair exhibit a relatively short interplanar distance laterally\nwithout significant face-to-face π–π overlap, the N⋯N distance between 3Abf\nmolecules in adjacent columns is 4.018 Å. This packing arrangement displays a loosely\npacked character (Figure R30a). Upon UV irradiation, energy is rapidly transferred,\ninducing swift molecular twisting within these disordered regions, thereby driving a\ndramatic irreversible phase transition that could result in macroscopic fragmentation of\ncrystals.\nIn contrast, the 3Abf-Tcpn cocrystals present a similar D-A arrangement pattern\n(Figure R30b), but its structure is stabilized by strong hydrogen bonds (N-H⋯N,\nC-H⋯N, and N-H⋯F) that form rigid dimers units (Figure R31), which further\nassemble into highly parallel and tightly packed DADA columns. This strong\nhydrogen-bonding network rigidly locks the molecular conformation, significantly\nrestricting the degrees of freedom for molecular motion in the excited state. Pure 3Abf\nadopts a classic herringbone packing motif driven by C–H⋯π interactions, the closest\nN⋯N distance measuring is as long as 7.312 Å (Figure R32), indicating molecules\nstruggle to achieve close-range cooperative motion through slip or rotation, preventing\nobservable macroscopic deformation.\nFigure R30. The columnar stack structure of 3Abf-Ofn (a) and 3Abf-Tcpn (b) cocrystals, respectively.\nFigure R31. The hydrogen bond interactions of 3Abf-Tcpn crystals.\nFigure R32.C-H⋯π interactions and N⋯N distance of 3Abf crystals.\nPage 12-13, line 342-357, five sentences have been added: “SCXRD analysis further\nreveals the self-assembly patterns and intermolecular interactions are key factors\ninfluencing photochemical processes. Pure 3Abf adopts a classic herringbone packing\nmotif driven by C–H⋯π interactions (Supplementary Fig. 44a), the closest N⋯N\ndistance is as long as 7.312 Å (Supplementary Fig. 44b), indicating molecules struggle\nto achieve close-range cooperative motion through slip or rotation, preventing\nobservable macroscopic deformation. The 3Abf-Tcpn cocrystals present D-A\narrangement pattern (Supplementary Fig. 45), but its structure is stabilized by hydrogen\nbonds interactions (N-H⋯N, C-H⋯N, and N-H⋯F) that form rigid dimers units\n(Supplementary Fig. 46), which further assemble into highly parallel, tightly packed\nDADA columns. This strong hydrogen-bonding network rigidly locks molecular\nconformation and significantly restricts the degrees of freedom for molecular motion in\nthe excited state. For the as-prepared 3Abf-Ofn crystals, intermolecular interactions are\ndominated by weak interactions (C–F⋯H, F⋯F and π-π) contacts, lacking strong\ndirectional hydrogen bond constraints between 3Abf and Ofn.”\nFigure R30-32 above have been added into Supporting Information as Figure S44-46.\n11. In page 12, line 317, does the fluorescence lifetime change from 3.93 to 4.00 ns, or\nfrom 4.00 to 3.93 ns? According to Supporting Information Figure 36, the fluorescence\nlifetime should exhibit an increasing trend, which differs from the previously observed\ndecrease in both fluorescence intensity and lifetime in the crystal (Figure 3c-f). What is\nthe reason for this discrepancy?\nAuthors’ response: We sincerely appreciate the reviewer's careful reading and\nconstructive suggestions. This is an important point. As suggested by the reviewer, the\nsentence has been modified: “Fluorescence lifetime slightly increases from 3.93 ns to\n4.00 ns”.\nThis apparent difference arises from the distinct optical response characteristics of\ncrystalline and film states. In single crystals, UV irradiation immediately triggers the\nphotochromic process, which is rapidly accompanied by a reduction in both\nfluorescence intensity and lifetime. This behavior can be attributed to photoinduced\nelectron transfer generating a nonemissive radical state and the self-absorption effect\n(Angew. Chem. Int. Ed. 2025, 64, e202422856). In contrast, the 3Abf-Ofn@PMMA\nfilm exhibits a dual-response optical behavior comprising two stages: initial\nphotoactivation followed by the photochromic process. Specifically, (1) during the\ninitial photoactivation process, UV irradiation induces minor molecular aggregation,\nsuppressing non-radiative decay pathways and slightly increasing the fluorescence\nlifetime from 3.93 ns to 4.00 ns; (2) under prolonged irradiation, the film undergoes\nphotoinduced fluorescence quenching driven by the photochromic process, which is\nconsistent with the fluorescence changes observed in the crystalline state. Meanwhile,\nelectron paramagnetic resonance (EPR) characterization reveals that the signal intensity\nincreases with prolonged irradiation time (Figure R33). These findings further confirm\nthe critical role of molecular packing and substrate rigidity in modulating the\nphotophysical properties of 3Abf-Ofn@PMMA films. (Adv. Funct. Mater. 2025,\n2502811).\nPage 15, line 414-416, one sentence has been added: “The fluorescence attenuation is\nattributed to photochromism induced by radical formation, as evidenced by enhanced\nvisible-light absorption (Fig. 5f) and increased in EPR signal intensity (Supplementary\nFig. 54).”\nFigure R33 below has been added into Supporting Information as Figure S54.\nFigure R33. EPR spectra of for 3Abf-Ofn@PMMA film before and after UV irradiation.\n12. In page 12, line 319, the authors doped cocrystal powders into a PMMA matrix.\nHow exactly can UV irradiation induce the movement and aggregation of molecules\nwithin the cured polymer matrix, given that 3Abf and Ofn were incorporated in\ncrystalline form rather than as freely mobile, unconstrained molecules? Reference: Adv.\nFunct. Mater. 2024, 34, 2411584. Additionally, the PMMA matrix thin films were\nprepared by mixing PMMA and the cocrystal powder in a dichloromethane solution.\nDoes the cocrystal dissolve in dichloromethane? Furthermore, what is the color\nvariation in the PMMA matrix films containing only 3Abf?\nAuthors’ response: We sincerely thank the reviewer for raising this important\nmechanistic question and for pointing us to the highly relevant work in Adv. Funct.\nMater. 2024, 34, 2411584. We have carefully studied this reference and revised our\ndiscussion accordingly.\nIn our cocrystal system, the 3Abf–Ofn cocrystal exhibits high solubility in\ndichloromethane, as shown in Figure R34. Therefore, during the fabrication of\ncocrystal@film, the 3Abf–Ofn cocrystal is dissolved in the PMMA/dichloromethane\ncasting solution. Upon rapid solvent evaporation, it re-precipitates as microcrystalline\naggregates within the PMMA matrix, evidenced by the broadened diffraction peaks in\nPXRD (Figure 5a), indicating a partial loss of long-range crystalline order. Under UV\nirradiation, although the 3Abf–Ofn molecules are largely immobilized and do not\ndiffuse freely, the polymer chains in PMMA exhibit local dynamic mobility (Adv. Funct.\nMater. 2024, 34, 2411584; Chem. Rev. 2018, 118, 5871-5911), enabling modulation of\nfree volume. In addition, light induces electronic excitation and transient charge\nseparation between 3Abf and Ofn molecules, generating localized spatial steric\nperturbations. Thus, the soft confinement environment of polymer matrix facilitates the\nphotoresponsive 3Abf–Ofn to undergo limited aggregation into emissive states.\nIn contrast, PMMA films doped with only 3Abf show very weak fluorescence and no\nsignificant color variation under same UV irradiation conditions (Figure R35). The\nUV/vis absorption spectra of 3Abf@PMMA films remain hardly changed before and\nafter UV irradiation, similar to that of the pristine 3Abf powder (Figure R36), indicating\nthat no structural changes under the same irradiation time. However,\n3Abf-Ofn@PMMA films show a new absorption band after irradiation, a trend that\nclosely corresponds to that of pure 3Abf-Ofn powder. These results demonstrate that the\noptical response behavior of the films relates to the necessary free volume and local\nsegmental mobility provided by the PMMA matrix, combined with the intrinsic\nphotosensitive properties of the cocrystal material.\nFigure R34. Photograph of a dichloromethane solution obtained by dissolving the 3Abf–Ofn\ncocrystal.\nFigure R35.The photographs and fluorescence emission spectra of 3Abf@PMMA films with different\nUV irradiation time.\nFigure R36. UV/vis spectra of 3Abf (a), PMMA(b) and 3Abf@PMMA(c) with different UV\nirradiation time.\nPage 15, line 402-405, one sentence has been added: “The behavior can be attributed\nto the intrinsic aggregation-induced emission (AIE) of 3Abf-Ofn\n(Supplementary Fig. 51) and UV-induced transient polymer chain mobility, facilitating\nmolecular ordered aggregates collectively 6,61.”\n[61] Shi, Y. et al. Achieving Swift and Distinct Luminescent Modulation Through\nManipulating Molecular Motion in Polymers. Adv. Funct. Mater. 34, 2411584 (2024).\nFigure R35, and Figure R36 have been added into Supporting Information as Figure\nS66, and Figure S69.\nMinor issues:\n1. In page 6, line 158, the term should specifically refer to “light-induced plastic\ndeformation” rather than the general “plastic deformation”, as the latter may cause\nambiguity. “Plastic deformation” typically describes the mechanical properties of\nmaterials. To avoid any potential misunderstanding, please revise it to \"light-induced\nplastic deformation.\"\nAuthors’ response: Thank you very much for the kind reminding. As suggested by the\nreviewer, we have corrected the “plastic deformation” to “light-induced plastic\ndeformation” in revised manuscript.\n2. In page 5, line 125, to be provided in the supporting information: How is the\noverlapping area determined?\nAuthors’ response: We appreciate the valuable comments by the reviewer. The\noverlapping area between Ofn molecules and 3Abf molecules in the co-crystal structure\nis quantified by crystal software and Adobe Photoshop as follows (J. Am. Chem. Soc.\n2020, 142, 1153–1158): (1) First, the crystallographic CIF file is imported into\ncrystallographic visualization software such as Mercury or Olex2 to display adjacent\n3Abf-Ofn molecular pairs, then the 3Abf-Ofn packing structure is rotated so that the\nviewing direction is perpendicular to the stacking plane, ensuring an optimal top-down\nprojection of the intermolecular spatial overlap. This orientation is exported as a\nhigh-resolution image in TIFF, PNG, or JPG format. (2) Next, the resulting image is\nimported into Adobe Photoshop. Using the “polygonal lasso tool”, both the overlapping\narea and the corresponding total area of 3Abf region are carefully outlined, respectively.\nThen “Image →Analyze →Record Measurements” is applied to obtain the area value of\ncorresponding selected region. (3) Finally, as shown in Figure R37. the degree of\noverlap is calculated as the ratio of the overlapping area to the total 3Abf molecular area\n(9793.00/10327=94.8291%)\nIt should be noted that this approach is semi-quantitative, which may be influenced\nby the precision of the software's drawing capabilities.\nFigure R37. The overlapping area determined by Adobe Photoshop.\n3. In page 5, line 125, “a sandwich-like structural motif” is more accurately described\nas “mixed stacking”, (−DADADA−). Please refer to Angew. Chem. Int. Ed. 2024, 63,\ne202416181 for proper description.\nAuthors’ response: We thank the reviewer for bringing this to our attention. We have\ncarefully reviewed the relevant literature and incorporated appropriate citations.\nTherefore, we replaced “a sandwich-like structural motif” with “mixed stacking” in the\nwhole manuscript according to the reviewer’s helpful suggestions.\nPage 5, line 125-126, one sentence has been revised: “forming a mixed stacking\nstructural motif (DADADA) through π−π interactions42”\n42. Wang, X. et al. Recent Advances of Organic Cocrystals in Emerging Cutting-Edge\nProperties and Applications. Angew. Chem. Int. Ed. 63, e202416181(2024).\n4. In page 5, line 128-130, the authors note that the two dihedral angles are “40.59 and\n48.72.” It would be helpful to indicate in the crystal structure diagram which specific\nmolecular dihedral angles these values refer to. The text mentions dihedral angles\nbetween adjacent molecules; however, for example, 3Abf molecules have neighboring\nmolecules along both the b- and c-axes. Additionally, in Figure 2e, the Ofn molecules\nconnected via F···F interactions appear to be parallel, rather than exhibiting a dihedral\nangle of “48.72.”\nAuthors’ response: We sincerely thank the reviewer for this careful and valuable\nobservation, which has significantly improved the accuracy of our structural description.\nUpon re-examination of the crystal structure (Figure R38), we confirm that the two\nrelevant dihedral angles for adjacent 3Abf molecules are 40.59° and 42.63°,\nrespectively. Additionally, as clearly shown in Figure R39, adjacent Ofn units linked by\nF···F contacts are nearly parallel, with a dihedral angle close to 0°. We apologize for\nthis error and any confusion it may have caused.\nPage 5, line 142-145, two sentences have been revised: “with the dihedral angle of\n40.59° and 42.63° (Supplementary Fig. 1). Likewise, neighboring Ofn molecules are\nlinked by F···F contacts, with no significant interplanar twist between adjacent\nnaphthalene rings (Supplementary Fig. 2).”\nFigure R38 and Figure R39 have been added into Supporting Information as Figure S1,\nand Figure S2, respectively.\nFigure R38. Dihedral angles for adjacent 3Abf molecules.\nFigure R39. Dihedral angles for neighboring Ofn molecules.\n5. In page 5, line 132, what is the intended purpose of the ESP simulation? Is it merely\nto demonstrate the existence of charge transfer, thereby contributing to subsequent\nmechanistic explanations? However, the electron spin resonance (ESR) spectroscopy\nresults indicate no radical signals before illumination, suggesting that the formed\nstructure is not a charge transfer cocrystal and that no charge transfer occurs. If these\nsimulations are redundant and fail to provide meaningful insights, they should not be\nincluded merely to bolster the content.\nAuthors’ response: We sincerely appreciate the reviewer's valuable suggestions and\nfully agree with them, as they have significantly enhanced the scientific rigor of our\nstudy. After careful consideration, we recognize that the ESP simulation presented in\nthe original manuscript could be misinterpreted as suggesting charge transfer in the\nground state. Therefore, we have removed the ESP analysis section from the revised\nmanuscript.\n6. In page 4, line 121, “the disordered Ofn units”. However, in the crystal structure, the\n3Abf units are disordered, the Ofn units are ordered.\nAuthors’ response: Thank the reviewer for the kind reminder. We sincerely apologize\nfor our carelessness, and have deleted “disordered” in the manuscript according to the\nreviewer’s helpful suggestions.\nWe hope our responses have fully addressed your concerns.\nReviewer #3 (Remarks to the Author):\nThe manuscript reports an intriguing cocrystal which exhibits photomechanical\nresponse. The results are of interest however raise more questions answers. After\ncareful reading of the manuscript, it can be realized that the manuscript lacks focus and\nis not supported by careful narration and explanations. Therefore, I don’t recommend\nthe publication of manuscript in Nat. Commun. For following general and specific\nreasons:\nAuthors’ response: We sincerely thank the reviewer for the thoughtful evaluation and\nvaluable suggestions of our work. All comments have been carefully considered and\naddressed in the revised manuscript and supplementary materials. We apologize for the\nunclear expressions and lacks focus in the original manuscript, which may have\ncontributed to the concerns raised. Your feedback has significantly strengthened the\nquality and clarity of our manuscript. We would be grateful if you could reconsider the\nrevised manuscript for publication.\nGeneral observations:\n1. Highlight of work is solid state dimerization of 3Abf molecules within a crystal on\nexposure to UV radiations. This is interesting, however can the strategy be extended to\nmore systems?\nAuthors’ response: We sincerely appreciate the positive and constructive comments\nfrom the reviewer, which we have addressed to the best of our ability. In addition to\n3Abf-Ofn cocrystals, we have conducted a series of supplementary experiments to\nextended this strategy to more systems, including 1Abf-Ofn, 2Abf-Ofn, 3Abf-Tcnb,\nand 3Abf-Tfpn. As shown in figure R40, only 1Abf–Ofn and 2Abf–Ofn show noticeable\ncolor changes, 3Abf-Tcnb and 3Abf-Tfpn remain structurally and optically stable under\nsame UV irradiation conditions. High-resolution mass spectroscopy (HRMS) results of\n1Abf–Ofn and 2Abf–Ofn after irradiation show clear signal located at m/z\n363.111[C H N O +H], consistent with the calculated mass for azo compounds\n24 14 2 2\n(Figure R41, and R42). In contrast, 3Abf-Tcnb, and 3Abf-Tfpn sample do not yield azo\ncompounds under identical conditions. This result not only reveals that the\nphotoinduced coupling strategy is not an isolated phenomenon confined to a single\nsystem, but also highlights the crucial role of Ofn in driving the reaction.\nAlthough we present a highly innovative and exploratory approach for fabricating\nphotoresponsive crystalline materials in the manuscript, the current focus remains on\nthe novelty of material design and the structure–property relationships. The reviewer’s\ninsightful suggestions have inspired us to consider an important future direction: could\nthe synergistic effect between cocrystal self-assembly and photo-induced synthetic\nmethodologies enable the expansion of azo coupling reactions beyond conventional\nsolution-phase approaches, which typically require toxic oxidants or elevated\ntemperatures? Combining the excellent optical properties of functional materials with\ninnovative synthetic strategies is expected to open a novel and efficient synthetic\npathway. In future studies, based on current findings, we will draw inspiration from\nsynthetic methodology and expand the scope of substrates to further explore the\nuniversality of this green strategy for synthesizing azobenzene derivatives, which\nrepresents our key research direction moving forward.\nPage 11, line 306-313, two sentences have been revised: “To elucidate the reaction\npathway from 3Abf-Ofn to Bfa, the control experiments with alternative electron\ndonors (1-aminodibenzofuran (1Abf) and 2-aminodibenzofuran (2Abf)) and acceptors\n(1,2,4,5-Tetracyanobenzene (Tcnb), 3,4,5,6-Tetrafluorophthalonitrile (Tfpn), and\n3,4,5,6-Tetrachlorophthalonitrile (Tcpn)) under identical conditions are conducted.\nBfa compounds can be detected (m/z 363.111) by HRMS upon UV irradiation of\n1Abf–Ofn (Supplementary Fig. 33) and 2Abf–Ofn (Supplementary Fig. 34), which\ndemonstrate that the strategy can be extended to more systems.\nFigure R41 and Figure R42 have been added into Supporting Information as Figure S33,\nand Figure S34, respectively.\nFigure R40. The photochromic photographs for 1Abf-Ofn, 2Abf-Ofn, 3Abf-Tcnb, and 3Abf-Tfpn\nbefore and after irradiation.\nFigure R41. High-resolution mass spectrum of 1Abf–Ofn.\nFigure R42. High-resolution mass spectrum of 2Abf–Ofn.\nWhat is the net chemical reaction leading to product formation and mechanical\nresponse is not explained clearly.\nAuthors’ response: We thank you for raising this important question. The net\nphotochemical transformation in the 3Abf-Ofn cocrystal system is a light-driven N–N\ncoupling reaction that yields an aromatic azo compound. In this pathway, UV\nirradiation triggers a photoinduced electron transfer from 3Abf to Ofn generating a\n3Abf radical cation and an Ofn radical anion. The 3Abf•⁺ radicals then undergo\nsubsequent deprotonation and coupling to form the final –N=N– linkage. This process\nis initiated by UV irradiation, which induces lattice strain due to photoinduced\nstructural mismatch between the product and the original cocrystal framework, leading\nto the partial release of the Ofn guest. The formation of azo compounds has been\nconfirmed by single-crystal X-ray diffraction and high-resolution mass spectrometry.\nDensity functional theory (DFT) calculations (Figure R43) are performed to support our\nproposed reaction pathway.\nFigure R43. Energy profile of the reaction by DFT calculations.\nMoreover, the accumulation of anisotropic stresses during the solid-state\ntransformation induces mechanical response. Local formation of azo products causes\ninternal strain through volume changes and molecular stacking rearrangements. When\nthe accumulated stress exceeds the mechanical stability limit of the crystal lattice,\nmacroscopic deformation occurs, as evidenced by observable crystal cracking.\nThese important sections have been explained and highlighted in a yellow background\nin the revised manuscript.\nPage 12, line 314-334, one paragraph has been added: “EPR results of 1Abf–Ofn\nand 2Abf–Ofn reveal the presence of radical signals by PET, accompanied by\nphotochromic behaviors (Supplementary Figs. 35–37). Notably, the reaction proceeds\nefficiently even under a nitrogen atmosphere, as evidenced by both Bfa product\nformation (Supplementary Fig. 38) and photochromic behavior (Supplementary Fig. 39),\nconfirming that this reaction is not a conventional oxidative coupling pathway with\nmolecular oxygen58,59. However, it is failed to observe color changes and yield\nazo compounds in 3Abf-Tcnb, 3Abf-Tfpn and 3Abf-Tcpn (Supplementary Fig. 40),\nunderscoring the crucial role of Ofn in driving the reaction. Based on the experimental\nfindings, we propose the reaction mechanism. Upon UV irradiation, photoinduced\nelectron transfer from the electron-donor 3Abf to the electron-acceptor Ofn generates\nradicals, which subsequently undergo intermolecular N–N coupling to form the\nazobenzene derivative Bfa. Density functional theory (DFT) calculations (Fig. 4f) are\nperformed to support our proposed reaction pathway. Upon photoexcitation, 3Abf-Ofn\nenters the singlet excited state, followed by intermolecular electron transfer to generate\nradical species. Subsequent the -NH₂• of 3Abf deprotonates to form -NH•, resulting in a\nreduction of the system energy to 0.89 kcal/mol. The generated radical then participates\nin N–N coupling process to yield an azo-linked dimer, and final product energy (1.43\nkcal/mol) is lower than the initial state, demonstrating that PET-assisted coupling\nreaction of 3Abf-Ofn is thermodynamically favorable.”\nFigure R43 has been added to revised manuscript as Fig. 4f.\n2. The introduction is not focused and does not provide a definite idea of developments\nin the area, instead is more generalized to describe cocrystals, which of course is not\nthe focus of work.\nAuthors’ response: We sincerely thank the reviewer for this valuable comment. In\nresponse, we have completely restructured the introduction to shift the focus from\ngeneral cocrystal concepts to the central scientific theme of our work.\nPage 3, line 71-87, five sentences have been added: “The unique structural tunability\nof cocrystals materials40-42 make them an ideal platform for exploring light-driven\nchemical reactions, as their ordered molecular packing can regulate the reactivity,\nselectivity, and kinetic behavior of photochemical processes effectively. The\nconvergence of crystal engineering and photochemistry is emerging as a promising\npathway for developing intelligent photoresponsive materials. Nevertheless, current\nresearch on photo responsive cocrystals remains predominantly focused on classical\nphotochemical processes, such as isomerization or cycloaddition reactions, with limited\nexploration of novel reaction pathways and their multifunctional outputs43. Therefore,\ndesigning co-crystal systems through supramolecular self-assembly to regulate\nphotochemical reactions, and further translating structure changes induced by chemical\nreactions into tunable functional properties, holds significant scientific importance.\nParticularly, the synergistic mechanism between guest release in cocrystal and\nphotochemical reactions, and how the cascade process transforms molecular-scale\nstructural evolution into dual optical-mechanical responses, has lacked systematic\ninvestigation.”\n3. The manuscript is not written carefully and leaves many questions unanswered. The\nlanguage shall be taken care of so shall be many claims, which are either contradict,\nincorrect or unsubstantiated.\nAuthors’ response: Thank you for bringing this to our attention. Based on your\nvaluable suggestion, we have thoroughly revised the entire manuscript to enhance the\nscientific rigor and readability of our work.\nSpecific comments:\nIntroduction: In generally introduction is not convincing and lacks the purpose. It needs\nto be reworked with better connection to current work, essentially supported by relevant\nliterature.\nAuthors’ response: Thanks for the suggestion. The introduction section has been\nrevised according to your feedback. We believe these revisions have significantly\nimproved the readability and scientific integrity of the manuscript. Should any section\nstill appear unclear or insufficiently substantiated, we would be grateful for further\nguidance and are fully committed to making additional revisions.\nI-1: The language used at multiple stages of manuscript is complex and difficult to\nfollow and the claims are not substantiated. For example, “Hence, it is crucial to\ndesign and develop a multifunctional crystalline materials system capable of sensing\nthe external environment through multi-level information output driven by distinct\naction mechanisms. Furthermore, it remains a challenge to convert the photoinduced\ndynamic mechanical motion of responsive materials into static luminescent modes\nwithin the same system to meet diverse material requirements. However, dynamic\ncrystalline materials that exhibit only single mechanical response characteristics\nstruggle to meet the diversified demands of technological advancement” and many\nmore.\nAuthors’ response: We sincerely thank the reviewer for this insightful and constructive\ncriticism. We have carefully revised the overly speculative and unclear language in the\noriginal manuscript. For example, the sentence you mentioned above has been modified\nto “Currently, many photo-responsive crystalline materials can dynamically respond to\nlight stimuli. However, research on integrating multiple distinguishable output signals\nfor a single material is still relatively limited 21” in Page 2 (line 44-46), and other\nsections needed for revision are highlighted in a yellow background in the revised\nmanuscript.\nI-2: “Sun et al. designed a series of biodegradable ferroelectric cocrystals of\ncholesterol-methanol and cholesterol-ethanol through the solvent effect.” These are\nbetter described as solvates than co-crystals. Of course there are better and strong\nexamples of co-crystals resulting in improved conducting, optical and pharmaceutical\nproperties.\nAuthors’ response: We sincerely thank the reviewer for careful reading. As suggested\nby the reviewer, we have removed this example and replaced it with one more relevant\nto our work.\nPage 3, line 68-71, one sentence has been revised: “Tang et al. reported triethylamine\nvapor induces a cyclization reaction in AOTC cocrystals, accompanied by a\ncocrystal-to-polycrystal phase transition process, converting the non-emissive\nfluorescence state of AOTC into a red-emissive ACTC cocrystal and a blue-emissive\nAIC39.”\n39. Zhu, L. et al. Triethylamine vapor-induced cyclization reaction in cocrystals leading\nto cocrystal-topolycrystal transformation. Nat. Commun. 16, 6441 (2025).\nI-3: “Photochromic fluorescent materials refer to photosensitive substances that exhibit\nchanges in color or fluorescent properties.” This is not true as photochromic materials\ncan be described like that not photochromic fluorescent materials.\nAuthors’ response: We sincerely thank the reviewer for this important clarification.\nWe agree with the reviewer's observation that the term “photochromic fluorescent\nmaterials” was indeed inappropriate in the original manuscript. Upon careful\nreconsideration, the sentence has been revised: “photochromism refers to a phenomenon\nwherein photosensitive substances undergo reversible changes in color upon exposure\nto specific wavelengths of light, driven by structural transformations or electronic\ntransitions, which are distinguished by pronounced color contrast and undetectable\nfluorescent signals under natural light22-26.”\nI-4: “In this work, we reported the example of photosensitive effect and photochromism\nin same organic molecular cocrystals, which are co-assembled by 3Abf and Ofn\nbuilding blocks driven by hydrogen bond interaction (Fig. 1).” The co-crystals are\nbased on pi-interactions rather than hydrogen bonds.\nAuthors’ response: Thanks for the reviewer's insightful and helpful suggestion. We\nhave replaced “hydrogen bond” with “π-π stacking interactions” in Page 3, line 90.\nResults and Discussion\nR-1: Symmetry unit = asymmetric unit\nAuthors’ response: Thank you for the kind reminder. We sincerely apologize for our\ncarelessness. To ensure an accurate description of the crystal structure, we have\nremoved the “symmetry unit” and revised the relevant sentence accordingly.\nR-2: one ordered Ofn molecule = ?; molecular order of 3Abf has been degraded during\n= ?; supramolecular molecular structures around the disordered Ofn units in the\ncrystal lattice = ?\nAuthors’ response: Thank you very much for the valuable comment. We have\nidentified several inaccuracies and errors in the original manuscript and have made the\nnecessary revisions and deletions.\nPage 5, line 130-132, one sentence has been revised: “Adjacent 3Abf molecules adopt\na head-to-tail stacking mode with close overlap and disordered conformations, which\nmay facilitate the susceptibility of the material to internal strain.”\nR-3: How can FT-IR spectrum evaluate phase purity and crystallinity?\nAuthors’ response: Thank you for your careful reading and valuable comment. We\nsincerely apologize for the inaccurate statement in the original manuscript. We highly\nagree with the FT-IR spectrum alone cannot evaluate phase purity and crystallinity. In\nthe revised manuscript, we have rephrased this as:\nPage 5-6, line 148-154, two sentences have been revised: “Furthermore, the phase\npurity and crystalline nature of the as-prepared 3Abf-Ofn during crystallization can be\nelucidated by powder X-ray diffraction (PXRD) analysis, which show good agreement\nwith the simulated pattern from single-crystal structure, the intense (002) diffraction\npeak indicates a preferred orientation (Fig. 2e). Fourier transform infrared (FT-IR)\nspectra indirectly reveals the formation of 3Abf–Ofn cocrystal containing both\ncharacteristic vibrational peak of building blocks (Supplementary Fig. 4).”\nR-4: “nitrogen radicals may occur during the light-induced electron transfer process”.\nWhy do authors rule out radical formed due to Ct interactions?\nAuthors’ response: Thanks for your professional comment. This is an important point.\nDensity functional theory (DFT) calculations of 3Abf-Ofn crystals reveal that the\nhighest occupied molecular orbital (HOMO) is mainly distributed to electron-donor\n3Abf molecules, while the lowest unoccupied molecular orbital (LUMO) is completely\nlocalized on electron-acceptor Ofn molecules, indicating electron transfer from 3Abf to\nOfn occurs efficiently. Upon UV irradiation, a new broad absorption band emerges in\nthe range of 370-450 nm, accompanied by an increase in absorption intensity,\nsuggesting the generation of light-induced species with radical character via electron\ntransfer process. (J. Am. Chem. Soc. 2020, 142, 2682–2689; Nat. Commun. 2022, 13,\n2646; Angew. Chem. Int. Ed. 2024, 63, e202401448). This assignment is supported by\nEPR spectroscopy, which shows a pronounced signal at g=2.004 after irradiation,\nconsistent with the presence of free radical formed during the electron transfer process\n(Angew. Chem. Int. Ed. 2025, 64, e202422856; Adv. Funct. Mater. 2024, 34, 2405877;\nNat. Commun. 2024, 15, 1455).\nAccording to relevant literatures, CT interactions in such cocrystals can promote the\nformation of ionization domains, triggering electron transfer from 3Abf to Ofn,\nresulting in the formation of the 3Abf⁺• radical cation. This cation rapidly undergoes\ndeprotonation at the amino group, yielding •NH radical, which serves as the key\nintermediate for subsequent N–N coupling. Thus, the donor–acceptor CT interactions\nprovide an essential structural foundation for efficient light-induced electron transfer\nand radical generation.\nR-5: “Furthermore, high-resolution mass spectrometry detects the formation of a\nnitro-containing intermediate during UV irradiation”.?\nAuthors’ response: Thanks for your insightful and helpful suggestion, which helped us\ncorrect a significant inaccuracy. Upon careful re-examination and additional HRMS\ncontrol experiments (Figure R44), we identified that the initial assignment of a\n\"nitro-containing intermediate\" was based on a misinterpretation of the HRMS signal in\nthe original manuscript. The observed peak at m/z 363.111 is unequivocally assigned to\nthe azo compound (C₂₄H₁₄N₂O₂) through exact mass matching, consistent with the\nproposed mechanism of radical coupling. Accordingly, the \"nitro-containing\nintermediate\" have been removed in the revised manuscript.\nFigure R44. High-resolution mass spectrum of 3Abf-Ofn sample after UV irradiation for 60 s (a) and\n2 h (b), respectively.\nPage 11, line 298-302, two sentences have been revised: “High-resolution mass\nspectrometry (HRMS) further confirms the formation of the final product Bfa\n(C₂₄H₁₄N₂O₂), with a detected m/z value of 363.111 matching the calculated exact mass.\nMoreover, the relative abundance of Bfa markedly increases from 20% to nearly 100%\nupon continuous irradiation for 2 h (Supplementary Fig. 30)”\nFigure R44 has been added into Supporting Information as Figure S30.\nR-6: “These experimental results confirm the light-induced structural transformation of\nthe 3Abf-Ofn compounds to Bfd photoproduct, which involves redox interactions with\nmolecular oxygen.”?\nAuthors’ response: Thank you for your insightful comment. We sincerely apologize\nfor the errors in the original manuscript and have thoroughly revised the reaction\nmechanism through a series of supplementary control experiments.\nAs we know, the synthesis of aromatic azo compounds under mild, atmospheric\nreaction condition using anilines as reactants is well-documented oxidative coupling\nreaction in both organic synthesis and solid-state photochemistry (Angew. Chem. Int.\nEd. 2010, 49, 6174 –6177; Angew. Chem. 2016, 128, 2211-2215; Chem. Sci., 2024, 15,\n13949–13957; Chem Catalysis. 2023, 3, 100472). In this system, the final photoproduct\nhas been clearly identified as an azo compound through single-crystal X-ray diffraction\n(SCXRD) and high-resolution mass spectrometry (HRMS). SCXRD analysis revealed a\ncharacteristic N=N bond length of 1.254 Å, confirming the coupling of two\n3-aminobenzofuran (3Abf) units into aromatic azo compounds. The observed peak at\nm/z 363.111 corresponds precisely to the calculated mass of the azo compound\n(C₂₄H₁₄N₂O₂), providing definitive evidence for the formation of the final product Bfa.\nBased on the experimental data, the light-induced structural transformation of the\n3Abf-Ofn cocrystal to Bfa photoproduct is proposed, which proceeds via a\nradical-driven pathway. Upon UV irradiation, photoinduced electron transfer from the\nelectron-donor 3Abf to the electron-acceptor Ofn, generating NH₂• radicals. Subsequent\nthe -NH₂• of 3Abf deprotonates to form -NH•. Then generated radical participates in\nN–N coupling process to yield an azo-linked dimer. Most notably, control experiments\nwith alternative electron acceptors (e.g., Tcnb, Tfpn, and Tcpn) under identical\nconditions showed neither photoproduct formation nor color change, underscoring the\nessential role of Ofn in this process. Moreover, the reaction proceeds efficiently even\nunder a nitrogen atmosphere, as evidenced by both Bfa product formation (Figure R45)\nand distinct photochromic behavior (Figure R46), confirming that molecular oxygen is\nnot involved in the reaction. Furthermore, our DFT calculations support our proposed\nreaction pathway (Figure R43).\nWe sincerely appreciate your valuable feedback, which has significantly advanced\nour comprehensive and in-depth understanding of the reaction mechanism.\nFigure R45 and Figure R46 have been added into Supporting Information as Figure S38\nand Figure S39.\nFigure R45. High-resolution mass spectrum of 3Abf-Ofn under a nitrogen atmosphere.\nFigure R46. The photochromic photographs for 3Abf-Ofn, before and after irradiation under a\nnitrogen atmosphere.\nR-7: I had been tried to read the manuscript very carefully to understand this: “This\ntransformation results in the release of guest Ofn molecules from the lattice,”,\nhowever I am not able to. Authors need to reconsider the writing of whole manuscript to make it\nlucid and self explanatory.\nAuthors’ response: We sincerely thank the reviewer for this valuable comment and for\ncarefully reading our manuscript. Upon UV illumination, the coupling reaction of 3Abf\nunits changes the cocrystal lattice, disrupting the structural complementarity between\nthe 3Abf and the Ofn. This mismatch induces significant internal strain within the\ncocrystal, triggering the release of guest Ofn molecules.\nPage 13, line 363-367, two sentences have been revised: “Meanwhile, Ofn is no\nlonger stabilized within the lattice due to loss of structural compatibility. Given its low\nmelting point and high vapor pressure60, Ofn readily sublimes even at room temperature,\nthus facilitating its escapes through sublimation as the temperature increases under UV\nirradiation.”\nAs suggested by the reviewer, we have carefully examined the whole manuscript for\nsimilar unclear phrasings and have revised them accordingly. All modified sentences in\nthe revised manuscript are highlighted in a yellow background.\nR-8: Is the co-crystal 3Abf-Ofn reproducible with disordered 3Abf? What causes\ndisorder of 3-Abf? Is the disordered co-crystals obtained by changing the solvents?\nThese questions need to be enquired to rule out the probabilistic nature of co-crystal\nformation, as authors themselves call it metastable phase. Authors further claim that\nclose proximity and disordered nature of 3Abf leads to its condensation, if the results\ncan not reproduced with other systems with control, the manuscript then losses larger\nimpact and relevance.\nAuthors’ response: We appreciate your professional comments. To further\ndemonstrate the reproducibility and structural origin of disorder in the co-crystal\n3Abf-Ofn, we have selected different solvent for crystal growth experiments, including\npure methanol, pure dichloromethane, chloroform, and their mixed solvents. The\ndisordered 3Abf moiety has been consistently obtained through crystallization process,\nconfirming that the disordered structure is not a random artifact, but a\nthermodynamically accessible and reproducible metastable form under ambient\nconditions.\nThe disorder of 3Abf molecule in the co-crystal 3Abf-Ofn arises from its\ncrystallographic placement on a special position. Specifically, although the 3Abf\nmolecule itself is non-centrosymmetric (orthorhombic system, Pna21 space group)\nlacking an inversion center, it occupies a site in 3Abf-Ofn (monoclinic system, P2₁/c\nspace group) where the local lattice symmetry is higher than the intrinsic molecular\nsymmetry (Figure R47). As a result, the molecule cannot fully conform to the imposed\ncrystallographic symmetry. To satisfy the symmetry constraints, the molecule adopts\ntwo symmetry-related orientations related by inversion, each with an occupancy of 0.5,\nleading to static positional disorder with partial occupancies. Therefore, this disorder is\na deterministic structural feature governed by symmetry requirements, and is unrelated\nto solvent changes.\nPage 5, line 133-136, one sentence has been added: “The disorder of the 3Abf\nmolecule arises from its crystallographic placement at a special position, as the local\nsymmetry of the lattice site is higher than the intrinsic symmetry of the 3Abf molecule,\nwhich crystallizes in the orthorhombic Pna2₁ space group.”\nFigure R47. The symmetry elements in 3Abf-Ofn cocrystal.\nR-9: Authors claim oxidation condensation of 3Abf within the crystal on exposure to hv,\nwhat is the oxidant within crystal lattice?\nAuthors’ response: We sincerely apologize for the erroneous description of \"oxidation\ncondensation\" in the original manuscript and has been removed. Through\nsupplementary experiments and mechanism validation, we have corrected the reaction\npathway: the formation of 3Abf into the azobenzene-type product Bfa proceeds via a\nradical coupling reaction rather than an oxidation condensation process. Specifically,\n3Abf–Ofn cocrystal undergoes photoelectron transfer from 3Abf to Ofn upon UV\nirradiation, generating radicals that undergo direct N–N coupling. Control experiments\nconfirm that no oxidant is required for this transformation. Furthermore, molecular\noxygen is not involved in either radical generation or coupling, as evidenced by the\nsuccessful formation of Bfa and the accompanying color change under a nitrogen\natmosphere.\nWe greatly appreciate your critical question, which prompted us to rigorously\nre-evaluate the reaction mechanism and eliminate the misleading oxidation-related\ndescription.\nAuthors also claim relase of Ofn, where does it go?\nAuthors’ response: Thank you for this important question. In fact, the photoreaction\nprocess is not a simple physical release of Ofn from an intact host framework. Instead,\nit involves an irreversible photochemical reaction of the 3Abf molecule itself, which\nfundamentally destabilizes the 3Abf-Ofn crystal lattice and enables Ofn release. To\nmonitor its fate, we conducted HRMS and XPS analysis for 3Abf-Ofn sample after\nirradiation. HRMS results show no signal attributable to Ofn (m/z 272.09 [M]⁺) can be\ndetected at various irradiation time. Additionally, XPS analysis reveals a significant\nweakening in the C–F signal (Figure 4e), further confirming the loss of F species from\nthe material. On the other hand, Ofn, as a derivative of naphthalene, has low melting\npoint (87-88 °C) and high vapor pressure, which makes it being easy to sublimate even\nat room temperature. During prolonged UV irradiation, the local sample temperature\nrises to approximately 50°C, which further facilitates Ofn sublimation. This\nphenomenon is corresponding to “where the low melting point (87-88 °C) and high\nvapor pressure of octafluoronaphthalene make it volatilize from the cocrystal with\ntemperature increasing” in Nature Communications, 2019, 10, 761. Therefore, we\nspeculate that Ofn may have departed via sublimation from the solid matrix.\nPage 13, line 363-367, two sentences have been revised: “Meanwhile, Ofn is no\nlonger stabilized within the lattice due to loss of structural compatibility. Given its low\nmelting point and high vapor pressure60, Ofn readily sublimes even at room temperature,\nthus facilitating its escapes through sublimation as the temperature increases under UV\nirradiation.”\nR-10 “This behavior may be attributed to the aggregation of molecules within the\npolymer matrix upon UV irradiation, triggering AIEE, which facilitates radiative\ntransition processes.” How is that possible?\nAuthors’ response: Thank you for the insightful and helpful suggestion. In\n3Abf–Ofn@PMMA film cast from dichloromethane, the cocrystals are initially\nmolecularly dispersed within the rigid polymer matrix, where unrestricted\nintramolecular rotation and vibration of the emissive component dominate non-radiative\ndecay pathways, resulting in weak initial fluorescence. Upon UV irradiation, the\n3Abf–Ofn@PMMA film undergoes the initial fluorescence enhancement, attributing to\nUV-induced transient polymer chain mobility, leading to reorganization of 3Abf-Ofn\nemissive species into ordered aggregates, thereby triggering aggregation-induced\nemission enhancement and a marked increase in fluorescence intensity.\nTo verify the applicability of such photoresponsive behavior, we further fabricated\n3Abf–Ofn doped films using other polymer matrices in dichloromethane (Figure\nR48-R50), including polylactic acid (PLA), polyamide (PA), and polyvinylpyrrolidone\n(PVP). The results shown that similar light-regulating behavior to that observed in\n3Abf–Ofn@PMMA films, indicating that the light-controlled aggregation-luminescence\nmechanism exhibits excellent reproducibility in various hydrophobic polymer matrices.\nTo ensure accuracy, we have revised “This behavior may be attributed to the\naggregation of molecules within the polymer matrix upon UV irradiation, triggering\nAIEE, which facilitates radiative transition processes.” to “The behavior can be\nattributed to the intrinsic aggregation-induced emission (AIE) of 3Abf-Ofn\n(Supplementary Fig. 51) and UV-induced transient polymer chain mobility, facilitating\nmolecular ordered aggregates collectively6,61”\nPage 15-16, line 428-441, four sentences have been added: “Replacing the PMMA\nmatrix with polyvinyl alcohol (PVA) matrix in aqueous solution, both 3Abf-Ofn@PVA\nfilm and 1Abf-Ofn@PVA film display only conventional photochromic behavior, with\na narrower excitation-dependent emission range (Supplementary Figs. 70-74). XPS\nspectra of 3Abf-Ofn@PVA show the presence of C-O-C and C-O-H bonding signals at\n533.38, and 532.35 eV, respectively (Supplementary Fig. 75). The strong bonding\ninteractions restrict molecular flexibility and promote fewer emissive state. Furthermore,\nwe further fabricated 3Abf-Ofn doped films using other polymer matrices, including\npolylactic acid (PLA), polyamide (PA), and polyvinylpyrrolidone (PVP) in\ndichloromethane. The results reveal that similar light-regulating behavior\n(Supplementary Figs. 76-80) to that in 3Abf–Ofn@PMMA film, demonstrating that the\nphotoactivated aggregation induced luminescence mechanism exhibits excellent\nreproducibility in various hydrophobic polymer matrices.”\nFigure R48-R50 have been added into Supporting Information as Figure S76- S78.\nFigure R48. Emission spectra mapping of 3Abf-Ofn@PLA film upon different irradiation time.\nFigure R49. Emission spectra mapping of 3Abf-Ofn@PA film upon different irradiation time.\nFigure R50. Emission spectra mapping of 3Abf-Ofn@PVP film upon different irradiation time.\nR-11: “fluorescence lifetime also decreases from 3.93 ns to 4.00 ns” =?\nAuthors’ response: Thank you for the kind reminder. We feel sorry for the wrong\ndescription. “fluorescence lifetime also decreases from 3.93 ns to 4.00 ns” have been\nrevised as “and fluorescence lifetime slightly increases from 3.93 ns to 4.00 ns”\nR-12: “forming a first-level fluorescence-based anti-counterfeiting mark” I doubt it is\ntrue.\nAuthors’ response: Thank you for bringing this to our attention. We acknowledge the\ninappropriate word choice and have revised it to “forming time-resolved fluorescence\nintensity anti-counterfeiting mark.” which can reflect the unique anti-counterfeiting\nprocess of cocrystal polymer films. The time-resolved characteristic endows the\nanti-counterfeiting mark with a dynamic verification signal that is difficult to replicate,\nenhancing the reliability of anti-counterfeiting identification.\nDiscussion:\nIt looks like conclusion, instead of discussion. No broader explanation and\nstructure-property correlations are established.\nAuthors’ response: Thank you for the insightful comment. We are very sorry for the\nmisunderstanding. Following the article format of Nature Communications in recent\nyears (Nat. Commun. 2025, 16, 8305；Nat. Commun. 2025, 16, 9158；Nat. Commun.\n2024, 15, 5401; Nat. Commun. 2024, 15, 5054; Nat. Commun. 2023, 14, 627), we have\nplaced the experimental discussion in the \"Results\" section and the conclusion in the\n\"Discussion\" section of the paper.\nHowever, we recognize that the structure–property relationships and broader context\ncould be presented with greater clarity. To address this, we have revised and\nstrengthened the conclusions in the \"Discussion\" section, with key enhancements\nmarked in a yellow background in the revised manuscript.\nWe hope our responses have fully addressed your concerns.\nREVIEWERS' COMMENTS\nReviewer #1 (Remarks to the Author):\nThe authors addressed most of my concerns, and now it can be published\non Nature Communcations.\nAuthors’ response: Thank you for your positive feedback. We sincerely\nappreciate your time and effort in reviewing our work.\nReviewer #3 (Remarks to the Author):\nThe manuscript is in better shape now and may be considered.\nAuthors’ response: Thanks very much for your positive comment and for\ntaking the time to review our manuscript. We are pleased that our responses\nhave addressed your comments satisfactorily."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors addressed most of my concerns, and now it can be published on Nature Communcations.", "reviewer_2": "[Editorial Note: Reviewer #2 submitted only comments to the editor, but had no remaining technical concerns]", "reviewer_3": "The manuscript is in better shape now and may be considered."}, "author_response": "Authors’ response: Thank you for your positive feedback. We sincerely appreciate your time and effort in reviewing our work. Authors’ response: Thanks very much for your positive comment and for taking the time to review our manuscript. We are pleased that our responses have addressed your comments satisfactorily."}]

Decision letter
Peer Review File
Dynamic Photochromism in Cocrystals and Tri-State
Fluorescence Switching in Films for Multilevel Optical
Encryption
Corresponding Author: Dr Shuzhen Li
This file contains all reviewer reports in order by version, followed by all author rebuttals in order by version.