High sensitivity pressure and temperature quantum sensing in pentacene-doped p-terphenyl single crystals

Domain: physics
Published: 2025-11-26
Editorial outcome: minor_revision

Abstract
Quantumsensors’responsivenesstotheirphysicalenvironmentenables
detectionofvariablessuchastemperature(T),pressure(P),andstrain.We
presentamolecularplatformforPTsensingusingpara-terphenylcrystals
dopedwithpentacene(PDP),leveragingopticallydetectedmagneticreso-
nance(ODMR)ofphotoexcitedtripletelectronspins.Weobservemaximal
frequencyvariationsofdf/dP=1.8MHz/barfrom0-8baranddf/dT=247kHz/K
from79–330K,over1200timesandthreefoldgreater,respectively,thanthose
seenwithnitrogen-vacancycentersindiamondand>85-foldgreaterpressure
sensitivityoverthepreviousrecord.Densityfunctionaltheorycalculations
indicatepicometer-levelPT-inducedmolecularorbitalshiftsaremeasurable
viaODMR.PDPoffersadditionaladvantagesincludinghighsensordoping
levels,narrowODMRlinewidths,highcontrast,andlow-costsinglecrystal
growth.Overall,thisworkreportslow-cost,optically-interrogatedPTsensors
andlaysthefoundationforincreasedversatilityofquantumsensorsthrough
syntheticmoleculardesign.

Introduction
Quantum sensors are revolutionizing the precise measurement of invasive sensing — capabilities often lacking in classical sensors
variousphysicalquantitiesbecauseoftheirinherentsensitivitytotheir (e.g.,thermocouples).
environment1.Whilesensorsconstructedfromelectronicspins,such Material properties, however, impose an overall bound on
as Nitrogen Vacancy (NV) centers in diamond2,3, are widely used as achievable sensitivity. For diamond NV centers the slope of varia-
sensitivemagneticfieldsensors4–7,thereisgrowinginterestintheir tionswithtemperatureandpressurearerespectively,∂D=71kHz/K
ability to probe other parameters, particularly temperature8,9, and∂D=1:46kHz/bar25,26;therigidityofthediamondlatticeresults
pressure10,strain11,12,electricfield13,androtation14,15.
inarelativelyweakpressure(andstrain)sensitivity11,27.Downstream
Sensing with NV centers and other quantum sensors levera- implications include an increase in the technical complexity
gesthesensitivityofthetriplet-statezero-fieldsplitting(ZFS),D, required for manipulating spins via strain12,28–30. This motivates
to temperature, pressure or strain, enabling their local, sub- exploration of alternative materials that also host a spin-optical
micron-scale, measurement16,17. Applications include nanoscale interface,similarto NV centers, whileofferingan enhanced sensi-
thermometry in single cells18–20 and probing phase transitions of tivitytothesephysicalparameters.
condensedmattersystemsinhigh-pressureanvilcells21–24.Optical Recent advances have highlighted the potential of molecular
interrogation of these sensors enables diffraction-limited, non- systemsforquantumsensing,utilizingrare-earthortransition-metal
ions31–34 or photoexcited organic radicals35,36. These systems offer
advantages stemming from bottom-up synthesis37, tunable sensor
placementinthree-dimensionsviaintegrationintoporousmaterials38
andmolecular-levelcontroloversensorproperties39.
Asaprototypicalunit,werecentlydemonstratedthatpentacene
moleculesdopedinpara(p)-terphenylexhibitexcellentspin-optical
properties and can be exploited for opticalmagnetometryat room
temperature (RT)40,41. The photoexcited triplet electron spin can be
opticallyinitializedandpossessesstate-dependentfluorescencecon-
trast,yieldingnarrow-linewidthopticallydetectedmagneticresonance
(ODMR)spectraatRT41.Additionally,thematerialcanbegrowninto
large single crystals (3 cm) with high doping levels ( ≈1000ppm),
relativetodefectsinsemiconductormaterials,andlowconcentration
ofbackgroundparamagneticimpurities.
In comparison to defects in semiconductor materials like dia-
mond,theweak,easilydeformable,p-terphenyllatticesuggeststhat
this material might exhibit heightened sensitivity to pressure and
temperature.Inthispaper,weshowthisthroughasystematicstudyof
photoexcitedtripletODMRspectraacrossawiderangeoftempera-
tures(79–330K)andpressures(0-8bar).Wemeasureapressureand
temperatureslope >1200-foldand >3-foldgreaterthanthatofNV
centers respectively, besides other operational advantages. First-
principles DFT calculations support experimental findings, provide
insightintooriginsoftheenhancedsensitivity,andsuggestpotential
forfurtherimprovementsindesignerchemicalsystems.Thesampleis
asingle-crystalofpentacenedopedp-terphenyl(PDP),dopedatthe
0.1% level. Figure 1A illustrates the lattice structure; x^ denotes the
molecular long-axis, with y^,z^ transverse to it. Crystals were grown
usingtheBridgmantechnique42,43afterzone-refiningthep-terphenyl
host and subliming pentacene for purification (see Supplementary
Note 1). Doping levels exceed those of defects in semiconductor
materials(e.g.,diamond)byatleasttwoordersofmagnitude.ThePDP
crystalscanbegrownuptoseveralcmatlowcost.Figure1Ccompares
typical PDP crystal sizes with diamond. The PDP crystal in Fig. 1C
requires only $2.06 in materials cost, representing a ~70,000-fold
reduction in mass-normalized cost compared to NV-diamond. Poly-
crystalline material can be obtained by crushing single crystals or
inducingimperfectgrowthtoformmm-scaledomains.
Figure 1 Bshows the energy leveldiagramofthe pentacene π-
elec(cid:1)tron in the p-terphenyl host. I(cid:1)t includes a ground state singlet
(∣S 0(cid:1)), an excited state si(cid:1)ngletE(∣S 1(cid:1)), and a metastable triplet state
(∣T )representedby∣T ,∣T ,∣T ,withlifetimesof ~35,166,and
1 x y z
500 μs44. The photoexcited triplet state is described by the spin
HamiltonianH =DðS2(cid:2)2Þ+EðS2(cid:2)S2Þ(1),whereSisaspin-1Pauli
sys z 3 x y
operator,withZFSparametersD≈1392MHzandE≈53MHz45.
Optical excitation populates the triplet state via intersystem
crossing(ISC)as∣S !∣T (seeFig.1B);withpulsedexcitation,
1 x,y,z
the∣T stateispolarizedto ≈76%46.Byselectingappropriatedelays,
x
spinstate-dependentfluoresce (cid:1) ncecon (cid:1) trastcanbeobtainedexploiting
differentialrelaxationfrom∣T 1 !∣S 0 ,inamannerthatisconditional
onthetripletsub-levels40,41.ThisproducesanODMRspectrum(Fig.1D,
E).Figure1DisthecaseforRTandEarth’sfield.Threetransitionsare
marked,hostingnarrowlinewidths,hereℓ 0 ≈4.3MHz,evenatthehigh
dopinglevelandwithpowerbroadening41.Thespectraherearewith
illuminationwithaCWlaser;pulsedlaserexcitationcanyieldhigher
ODMR contrast ( ~17%)41. Asymmetric lineshapes are influenced by
hyperfinecouplingstoneighboring protonnuclei.Inversionofcon-
trastfortheT ð∣T $∣T Þtransitionsisduetohighersteady-state
yz y z
populationin∣T z than∣T y 41.ForT xy ,theelectroniccoherencetime
was measured at TDD(cid:3)18 μs under dynamic decoupling, with
T =23μs,dominatedbytriplet-groundrelaxation41.
1
AsschematicallyshowninFig.1A,weinvestigatechangesinthe
ODMRspectraundervaryingtemperatureorpressure,whichaffect
thehostlatticeandtheZFSparameters,DandE.Figure1Fillustrates
theexperimentalsetup.Thesampleisplacedinavariable-temperature
flow cryostat(Janis ST100) or a pressurechamber.Experiments are
conducted on a sub-ensemble of ~109 pentacene molecules over
2.6×10−5mm3.
Figure 1 E shows a typical result. Compared to the RT ODMR
spectrum (Fig. 1D), lowering the temperature to 79 K causes a
noticeableshiftinthepositionsofthethreetransitions,ashighlighted
bythedashedverticallines.

Results
TripletODMRvariationwithtemperature
Toinvestigatethespectralchangeswithtemperature,Fig.2presents
dataacrossawiderange(79-330K).Figure2A(i,ii)showsindividual
ODMR traces for T xy and T xz , with color gradients (blue-to-red)
representing increasing temperatures. The temperatures are
measuredatthecryostatcold-fingerandhaveaconstantoffsetfrom
theactualsampletemperatureduetolaserinducedheating.Adashed
lineparalleltothetemperatureaxisservesasavisualguide,makingthe
spectral shift immediately apparent. The movement of the peaks is
indicatedbytheblackarrows.
Figure 2B(i) shows the extracted ODMR peak positions for T
xy
transitionestimatedfromthecenterofthesteepspectraledge,plot-
ted against the measured cold-finger temperature. The data reveal
threedistinctlinearregions,labeledI−IIIandshadedforclarity.The
strongvariationaroundregionII)hasthecharacteristicsignatureofa
phasetransitioninthep-terphenylmolecules47,48.Fromtheliterature,
this phasetransition occurs at 193 K49; thisismarked in Fig.2B for
clarity.
Figure2Cschematicallydepictsthelatticediagramsofthetwo
phases,transitioningfromtriclinicinregionItomonoclinicinregion
III.Thestructuresaresimilar,exceptforthecentralp-terphenylben-
zene ring, whichis out-of-plane inthe triclinicphase. While related
signatureshavebeenobservedpreviouslyinphotoluminescence50,to
ourknowledge,Fig.2BmarksthefirsttimeanODMRmeasurementis
carriedoutdirectlyataphasetransition.Overall,Fig.2Bdemonstrates
thatpentacenemoleculesaresensitivereporterstochangesinthehost
latticeconfiguration.
TheredlinesinFig.2B(i)showlinearfitstotheODMRvariationin
thethreeregions.TheslopeinregionIIisaboutthreetimesthatofthe
variationindiamond(seeTable1foradetailedcomparision).Asthis
phasetransitionisreversible,itmayserveasanexcellentbiaspointfor
quantum sensing thermometry. We anticipate another sharp, albeit
irreversible, phase transition at the melting point around 486
K(absolutetemperature).
Figure2B(ii,iii)showscorrespondingvariationsfortheT
yz
andT transitionsrespectively.Thestepvariationatthephasetransitionis
xz
visibleinbothcases.T exhibitsanapproximatelylineardependence
yz
over the entire temperature range studied, and constitutes a wider
linear dynamic range than in NV-diamond51. From a practical per-
spective,thecomplementaryuseofthesteepT transitionandthe
yz
linearT transitionallowsforbothhighsensitivityandalargedynamic
yz
rangeintemperaturesensingwithinthesamesystem.
Figure2DpresentstheextractedchangesintheZFSparameters
with temperature, D(T)and E(T). Table 1 compares thesevariations
withotherquantumsensingmaterials,includingNV-diamond,silicon
vacancies(V(cid:2))insiliconcarbide(SiC)(shownarevaluesfortheexcited
Si
state),andnegativelychargedboronvacancies(V(cid:2))inhBN.Thethird
B
column, df/dT, represents the change in spectral frequency with
temperature.Forpentacene,weobserveavariationof247kHz/Kfor
T inregionIIand101kHz/KforT inregionIII(redlineinFig.2B(iii)),
xy xz
bothsteeperthanthevariationinNV-diamond.
Figure2EnowexaminesvariationsinODMRcontrast,focusingon
the T transition (see Supplementary Note 2 for other transitions).
xy
Contrastincreasesslightlyatlowertemperaturesbutshowsasharp
change near the phase transition in region II. Another drop occurs
after the plateaupast290 K, likely due to exciton delocalization at
elevated temperatures and increasing temperature decreasing the
polarizationlifetimeandchangingtheintersystemcrossingratesand
tripletdepopulationrates.Notably,muchhigherabsolutecontrast(up
to17%)canbeachievedusingpulsedlaserexcitation41,andweexpect
similarcontrastvariationsasshowninFig.2Eeveninthiscase.
To evaluate the time-normalized temperaturesensitivity of our
measurements, we use ηT=σ τ=dS (2)52, where dS is the maximum
dT dT
ODMRsignalslopewithtemperature,σisthenoisefloor,andτisthe
integrationtime,definedbythelow-passfilter’ssettlingtimeinthe
detectionlock-inamplifier.Thisdefinitionincorporatesbothintrinsic
properties(e.g.,spectralshift)andextrinsicfactors(e.g.,noiselevel
andintegrationtime),andthusservesasacomprehensivefigureof
meritforcomparingdifferentexperimentalsetupsandmaterialsys-
tems.Oursetupisnotoptimizedforsensitivity;wecollectonlyasmall
fractionofphotons,andtheODMRcontrastinFig.2Eislowdueto
continuous-waveillumination.Bothfactorscouldbeimprovedbyat
leastanorderofmagnitude41.
Evenso,inregionIIoftheT
xz
transition(Fig.2B(iii)),weesti-
mateasensitivityofηT=0.04kHz/K.ThefourthcolumnofTable1
shows the best reported values fromothersystems. Adirect com-
parisonischallenging,assensitivitydependsonmanymeasurement
parameters, such as photon collection and the number of spins
interrogated.Nevertheless,evenwithourcurrentsetup,pentacene
outperforms defectsinSiCand hBN,partiallyduetothe narrower
ODMR linewidth53 (first column in Table 1). With straightforward
improvements, we anticipate approaching NV-diamond sensitivity;
already however pentacene already offers significant deployment
advantages due to the ease of crystal growth and lower cost
(seeFig.1C).

TripletODMRvariationwithpressure
AnanalogousstudywasconductedforODMRvariationwithapplied
isotropicpressure,showninFig.3foralowabsolutepressurerange
(0–8bar).Figure3A,BpresentsrepresentativeODMRtracesfortheT
yz
andT transitionsonly,sincetheT transitionisnotassensitiveto
xz xy
pressureovertheappliedrangesstudied(seeSupplementaryFig.S4).
Thetracesshowminimalspectralbroadeningwithappliedpressure,
alongwithadiscernibleshiftinthepeakposition.IncontrasttoNV-
diamond which is more suited to high-bias pressure environments,
Fig. 3A, B demonstrates the ability for measurements at close to
ambientconditions.Fig.3
CshowsthevariationinODMRtransitionfrequenciesforthe(i)
T and(ii)T transitions,similartoFig.2B.Asexpected,nolattice
yz xz
phasetransitionoccurswithinthepressurerangestudied.Thevaria-
tioninFig.3Cisweaklynonlinear,butforsimplicity,weestimatetwo
linearslopesoverthemeasuredrange,indicatedbytheredlines.For
theT transition,weestimateadf/dPvariationof1.8MHz/Barinthe
xz
(1–2Bar)rangeand350kHz/Barinthe(3–8Bar)range.Variationfor
theT transitionissimilar:1.4MHz/Barinthe(1–2Bar)rangeand362
yz
kHz/Barinthe(3–8Bar)range.
AsshowninthefifthcolumnofTable1,themaximumvariation
hereisatleast1200timesgreaterthanthatofNVcentersindiamond,
and even larger for the case of V(cid:2) in SiC. This difference can be
Si
attributed to the relative weakness of the p-terphenyl lattice; also
reflected in the lower Young’s modulus in p-terphenyl (70 kBar54)
compared to diamond (12 MBar) and SiC (4.5 MBar)55. Figure 3D
presentstheextractedD(P)parameter,whileE(P)remainsapproxi-
matelyconstantovertherangestudied(seeSupplementaryNote3,
secondparagraph)49.
Figure3EshowsthevariationinODMRcontrastoverthepres-
sure range, for the (i) T and (ii) T transitions respectively. The
yz xz
contrastisapproximatelyconstantthroughouttherange.Underthe
current conditions,time-normalized pressure sensitivity can be
evaluatedasηP=σ τ=dS(3),andisreportedinthesixthcolumnin
dP
Table1.Evenwithoutoptimization,thepressuresensitivityforPDP
(≈0.07Bar/ Hz)significantlyoutperformsthebestreportedvalues
for other platforms, while operating in a convenient range near
ambientpressure.

DFTcalculations
To understand these trends, we perform density functional theory
calculationsusingaplane-wavebasissetandnorm-conservingpseu-
dopotentialsasimplementedintheQuantumESPRESSOcode56.We
useakineticenergycutoffof60Ry,andadoptspincollinearPerdew-
Burke-Ernzerhof(PBE)astheexchange-correlationenergyfunctional.
Initialcrystalstructuresofmonoclinicandtriclinicp-terphenylwere
obtainedfromref.57.Onepentacenemoleculeissubstitutedintothe
M4position58,andthegroundstatestructuresarefurtheroptimized
untiltheHellmann-Feynmanforcesoneachatomaresmallerthan10−5
auinmagnitude.Weusea1×1×2supercellcontaining1pentacene
moleculeand15p-terphenylmolecules.Brillouin-zoneintegrationsare
sampledonauniformgridof2×2×1k-points.Tosimulatetheopti-
cally excited triplet state, we follow the ΔSCF method59, fixing the
occupationssothatthehighestoccupiedmolecularorbital(HOMO)of
pentacenecontainsonespin-upelectronandthelowestunoccupied
molecularorbital(LUMO)ofpentacenecontainsonespin-upelectron.
RenderingsoftheseorbitalsareshowninTable2A.
Wefocushereontherestrictedquestionofcomputingthechange
ΔDcorrespondingtothephasechangebetweenmonoclinicandtri-
clinicinFig.2B,D.Betweenthemonoclinicandtriclinicphases,wefind
relative shifts between the pentacene HOMO and LUMO centroid
positionaswellasdecreasesinthespreadoftheseorbitals.Orbital
spreads are generally smaller in the monoclinic phase by 1 ~5pm
(Table2B).Latticeconstantsinthemonoclinicphasearelargerthan
the triclinic phase by about 0.2 Å in the a, c directions, leading to
reducedintermolecularinteractionsandtighterlocalizationofmole-
cularorbitals.Becauseofthecrystalfield,pentaceneorbitalsarenot
perfectly centered on the molecule. In particular, orbital centroids
shift by 1 ~4pm between monoclinic and triclinic phases, with the
largestrelativeshiftalongthelongmolecularaxis(x^).
Thesechangesinthemolecularorbitalsleadtodifferencesinthe
zero-field splitting tensor between the two phases. The spin-spin
interactionHamiltonian60is
1μ X D r2δ (cid:2)3r r E
D
ab
=
24π
0ðg
e
μ
B\Þ2 χ
ij
Φ
ij
∣ ab
r5
a b∣Φ
ij
ð1Þ
i<j
for all electron pairs Φ ðr,r0Þ=p1ffiffiðϕðrÞϕðr0Þ(cid:2)ϕðrÞϕðr0ÞÞ (5) and
ij 2 i j j i
χ =±1forparallel(+)/anti-parallel(−)electrons.Consideringjustthe
ij
contributionfromthepentaceneHOMOandLUMOorbitals,wefind
differences in D eigenvalues between the monoclinic and triclinic
phasesofupto4MHz(Table2B),whichisthesameorderofmagni-
tudeastheexperimentallyobservedfrequencyshifts(Fig.2B).
Furthermore,theT frequencyshiftsthemost,asaresultofthe
larger orbital shifts alon x g the x^ direction, agreeing with the experi-
mental observation of T and T transitions shifting the most.
xy xz
Includingcontributionsofall1392electronsinthesystemtoD is
computationallyunfeasible.Weexpectthesecontributionstochange
theexactvaluesoffrequencyshifts,whileremainingatthesameorder
ofmagnitude.Wemayestimatethechangeinthespin-spininteraction
ΔD
(cid:3)
in 2
μ
π0
ð
μ
B\Þ
2
Δ
(r
)
.
T
ha
k
ing
typ
a
l
v
a
l
u
e
s
o
f
orbital
sp
re
ad
≈
3
.7
Å
, we estimate ΔD ≈1 MHz. This analysis shows that picometer scale
changesinmolecularorbitalsaremeasurablebyODMRpeakshiftsat
theMHzscaleforsuchsystems.

Methods
Samplepreparation
The procedure to crystallize pentacene-doped p-terphenyl was
adapted from Oxborrow et al.70. p-terphenyl (≥99.5% purity) and
pentacene (99% purity) were purchased from Sigma-Aldrich. To
further purify these raw materials, p-terphenyl was loaded into a
borosilicate tube (I.D.: 8mm, O.D.: 10mm) and sealed under
vacuumandinertatmosphere.Thetubewasthenpassedthrough
>30 rounds of zone refinement. Pentacene was purified via sub-
limation under continuous Ar (99.999% purity) supply in a bor-
osilicatetube(I.D.:8mm,O.D.:10mm)inthedarktopreventlight-
induceddisproportionationreactions71,72.Underinertatmosphere,
a 1:1000 (w/w) ratio of purified pentacene and p-terphenyl was
groundinamortarandpestlevialiquid-assistedgrindingwithafew
drops of toluene and loaded into a homemade borosilicate glass
crystal growth ampule (I.D.: 8mm, O.D.: 10mm). The ampule was
flame-sealedundervacuumandinertatmosphereandloadedinthe
growth furnace. A preprogrammed stepper motor gradually low-
ered the ampule through a temperature gradient at 5mm/hr to
producepentacene-dopedp-terphenylsinglecrystalsfollowingthe
Bridgmanmethoddescribedinrefs.73,74.

FurtherdetailsofODMRsetup
Here, we provide additional details about the experimental setup
usedinourstudy.Theexperimentswereconductedusingacustom-
builtapparatus.Forthetemperaturesensingexperimentsthesample
wasplacedinavariable-temperatureflowcryostat(JanisST100)as
shown in Fig. 1F. Figure 4 shows the setup used to record ODMR
spectra forpressuresensing.Thesamplewasplaced ina pressure
chamber, with pressure maintained using the pressure gauge,
transducer,trap,andpump.A532nmcontinuouswavelaser(532nm
2WCoherentVerdiG2)wasusedforsampleexcitation.FortheCW-
ODMR experiment, the sample was continuously illuminated. The
laser was reflected towards the sample with the help of a 550 nm
long-pass dichroic mirror (D; Thorlabs DMLP550). The laser beam
wasfocusedonthesampleatthefinallens(focallength50mm),and
the emitted photoluminescence (PL) was also collected using the
same lens. Emitted PL waspassed through the dichroic mirror, fil-
teredwitha600nmlong-passopticalfilter(F;ThorlabsFEL0600),
and then focused on the avalanche photodiode (APD; Hamamatsu
C12703 DC-10MHz) with the help of another lens. The signal from
APDisrecordedwithaLock-inamplifier(SRSmodelSR830DSP).The
laserpowerreachingthesampleis ≈110mW.
Radiofrequencyandmicrowavesignalsweregeneratedusing
an arbitrary waveform transceiver (AWT) from Tabor Electronics
(ModelP9484M).WeoperatedtheTaborAWTonNCOMode.The
generated RF or MW was passed through an RF-Switch (Mini-Cir-
cuits ZASWA2-50DR-FA+) before amplification with RF- and MW-
Amplifier(EmpowerRFSystems1079-BBM1C3K7GandMini-Circuits
ZHL-2W-63-S+, respectively). The RF was fed to the sample (S)
through a 3mm diameter 1-turn coil. The sample size is 2mm×
2mm×0.9mm and sits in the middle of the coil, which is termi-
natedbya50Ohmresistor.TheMWpowerreachingthesamplewas
≈1Wforpressuresensingexperimentsand ≈0.3Wfortemperature
sensingexperiments.

Contrastmeasurements
As mentioned above, the PL is collected using convex lenses and
convertedintoanelectricalsignalusinganAPDmodule.Thiselectrical
signalisdemodulatedusingalock-inamplifier,whosereferencesignal
modulatestheRF(ON/OFF)at1kHz.TheODMRcontrastisdefinedas
the difference in the PL signal when the RF power is ON and OFF,
dividedbythePLsignalwhentheRFisOFF.ToexpresstheODMR
contrastasapercentage,thecalculatedcontrastismultipliedby10075.

Dataavailability
The ODMR data generated in this study has been deposited in the
Zenodo repository76 and is available at (https://doi.org/10.5281/
zenodo.17231876).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Please, see attached file for my comments.", "reviewer_2": "In the submitted manuscript, the authors report on the utility of pentacene-doped in p-terphenyl host lattice as pressure and temperature sensor. The main idea behind the study is the leveraging of flexible nature of molecular crystals, relative to the well-investigated diamond lattice hosting NV centres, as a better sensor material. The manuscript is well-structured and fundamental concepts are eloquently presented. The authors need to address the following the comments to determine the suitability of the script for publication in Nature Communications.\n\nTitle:\nThe term organic crystals is rather general. I think, the title would be more informative, if the authors use “pentacene-doped p-terphenyl single crystals” instead of organic crystals.\n\nAbstract:\nPlease mention temperature and pressure ranges studied.\n\nI. Introduction\n1. The authors cite references 28 and 29 as dealing with rare-earth ions. While it’s true 29 deals with rare-earth ion (Eu3+), the reference 28 deals with Cr4+ molecules, a transition metal system. Please correct this discrepancy by rewriting the sentence. There is a typo: “utilizing are-earth ions”\n2. What does the authors mean by tunable sensor placement in three-dimensions? Please elaborate.\n3. For easy referencing, the authors can give values for the size of the single crystals and doping levels of sensor molecule in a host.\n\nII. System and principle\nDoes the doping concentration affect the sensing capability of the system?\nThe figure 1E is labelled with 79 K, while the text says 77 K.\nPlease show the TXZ linewidth at 79 K (77 K?)\n\nIII. Triplet ODMR variation with temperature\nIn Figure 2C, the authors can add temperatures for easy referencing of temperature-dependent phase change.\nSince pentacene performs a useful function, the authors can write “sensitive reporters” instead of “sensitive spectators”\nIn figure 1D and E, the ODMR frequencies of XY and XZ transitions increase with decreasing temperature. However, in figure 2A, for XY, the trend seems opposite. I am a bit confused how to interpret the data presented in the figures. Probably, I am missing a point here.\nThe attribution of drop occurring after 290 K to the crystals being close to the melting point (486 K, as mentioned by the authors) is rather tentative. The issue is compounded by almost 200 K difference. Could the authors provide a more logical explanation?\nApart from the frequency shift with respect to temperature, the intensity of the ODMR transitions seems to change with temperature. Could this intensity variation used to sense temperature, more like luminescence thermometry (https://doi.org/10.1002/adma.202302749) reported for luminescent molecular and solid-state systems? It would be interesting, if the authors make a comparative study between intensity and frequency variation with respect to temperature.\n\nIV. Triplet ODMR variation with pressure\nWhy the authors chose to study Tyz and Txz transitions? What is the rationale behind leaving out the Txy transition?\n\nVI. Conclusions\nI do agree with the authors that the studied system is interesting. However, I have difficulties accepting the system as a compelling pressure and temperature sensor. The same applies to the “elimination of reliance on electronic defects…” In my humble opinion, the statements are far-fetched and require rewriting.\nCould the authors discuss how the chemical design strategies can be leveraged to improve the sensitivity of the crystalline system discussed in the manuscript? For example, could deuteration enhance the optical properties with the consequent effect on sensing capability?\n\nA minor remark:\nThere is always a space between value and unit: for example, please correct 77-330K in the introduction, in the caption of Figure 1, and other parts of the manuscript.", "reviewer_3": "Singh et al. described a quantum sensing system based on pentacene in p-terphenyl crystals, which demonstrates high sensitivity to temperature and pressure through shifts observed in optically detected magnetic resonance (ODMR) spectra. While the study presents the novelty of using ODMR to measure these parameters, it is important to note that several key aspects of the work are already well documented in the literature. These include the use of pentacene triplet spin states for quantum sensing, the application of ODMR (and EDMR) to address these spin states, and the sensitivity of pentacene triplet states to both temperature, including phase changes, and pressure (e.g., ref 42, https://doi.org/10.1021/jp070251v). Given that pentacene triplets are a well-established molecular platform, it is not surprising that the authors were able to optically detect spectral shifts and utilize them to sense these parameters. Nevertheless, I recognize that the use of emission-based detection in this context is a novel contribution, and I could potentially support the acceptance of the manuscript.\n\nHowever, I would like the authors to address how they envision using this system as a sensor in real-world applications.\nSpecifically:\n• What types of target environments would this sensor be used for?\n• Why are such capabilities necessary or advantageous in those contexts?\nThe authors claim that the pentacene triplet system exhibits higher sensitivity compared to defect-based systems such as nitrogen-vacancy (NV) centers. While this may be true, it is important to recognize that NV centers have been successfully implemented in both single-crystal and surface platforms for sensing these parameters in well-defined settings. The performance criteria listed in Table 1 have limited significance if they cannot be realized under practical conditions or if the system cannot be effectively deployed in its intended applications. For example, the authors highlight the phase transition region values for df/dT at 193 K to demonstrate a significantly larger sensitivity than NV centers. However, what is the practical relevance of this temperature in real-world sensing applications? A similar concern applies to pressure measurements—what is the significance of detecting variations in the 1–2 bar range? Without clear justification for these conditions, the claimed advantages of the pentacene system may not translate into meaningful practical benefits, and the presented results do not carry significant weight or novelty.\n\nOverall, the methodology and data presented appear reasonably sound. I would recommend addressing these points to strengthen the paper's relevance and provide a clearer vision for its potential applications.\n\nMinor comments:\np2: “The PDP crystal in Fig. 1C requires only $2.25 in materials cost, representing a ∼70,000-fold reduction in mass-normalized cost compared to NV-diamond.” This requires either citation or some support for the numbers.\np2: “Fig. 1D the case for RT and Earth’s field.” Missing is?", "reviewer_4": "MANUSCRIPT NCOMMS-24-69634:\n“High sensitivity pressure and temperature quantum sensing in organic crystals”\nReferee Comments are in Black; Authors’ Response are in Blue\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 1\nThe data presented are very clear, accurate and, overall, of good quality.\nWe thank the referee for their praise for the clarity, accuracy, and overall quality of the manuscript!\nThe comparison with the pressure and temperature sensing performed over different spin centers (such as\n– but not limited to - Nitrogen-Vacancy centers) allows us to appreciate the potential of molecular spins as\nsensors.\nWe are glad that the referee found the tabulated comparison between different pressure and temperature\nsensing platforms useful.\nNotably and very interestingly, the final part of the manuscript contains DFT results which support the data\nand suggest the possible origin (at molecular orbital level) of the advantage of molecular spins for sensing\npressure and temperature if compared to other magnetic spin impurities.\nWe thank the referee for appreciating the valuable theoretical underpinnings in our argument.\nIn my opinion the manuscript, in its actual version, is for sure reporting a molecular-based pressure and\ntemperature quantum sensor, highlighting potential advantages with respect to other paramagnetic spin\ndefects or impurities and a possible explanation about the origin of such advantages.\nWe thank the referee for their favorable assessment of the manuscript, the potential of the molecular\npressure and temperature sensing platform presented, and fundamental work to understand the system’s\nproperties.\nOverall, the results meet the level required for a publication in Nature Communications. However, at the\nsame time, I have several points the authors must necessarily address before recommending the manuscript\nfor publication. Please find below additional points and comments:\nWe are grateful to the referee for deciding that the revised manuscript meets the high standards of Nature\nCommunications and for their recommendation to publish the revised manuscript.\n1) References. In my opinion there are some missing references concerning sensing or quantum sensing of\npressure and temperature. For instance, Ref. (5) in the caption of Table I, although mentioned in the table\nand used for comparison, is not appearing in the reference list. The same seems to occur also for Ref. (6),\n(8) and (9) of the same Table I. These works should be included in the reference list and properly cited (in\nthe introduction and/or in the discussion part) since the authors are basing on their results to show the\npotential of their molecular sensor.\nHere's possible other works the authors could consider to cite:\n- https://www.nature.com/articles/s41467-024-52272-y\n- https://www.tandfonline.com/doi/full/10.1080/26941112.2021.1964926\nWe appreciate the referee’s suggestion of these additional references. We have now updated the manuscript\nto include these works in the main reference list and included the references of Ho et al. and Wang et. al.\nThe formatting issues with Table I references have also been corrected.\nIt seems also that Ref [33] of the manuscript has been recently published and it is no more a preprint:\nhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.120801\nWe have updated the manuscript to include the published version in the reference list.\nThe introduction mentions the potential of molecular spins systems for quantum sensing. In my opinion,\nthe authors are missing some recent developments on both the theoretical as well as the experimental side,\nwhich should be added to the references:\n● https://iopscience.iop.org/article/10.1088/2058-9565/ad985e\n● https://www.nature.com/articles/s41534-024-00838-5\n● https://www.sciencedirect.com/science/article/abs/pii/S0304885319311199?via%3Dihub\n● https://www.nature.com/articles/s41565-024-01724-z\n● https://pubs.acs.org/doi/10.1021/jacs.2c07692\n● https://pubs.aip.org/aip/jcp/article/158/16/161103/2885321/Toward-quantum-sensing-of-Chiral-\ninduced-spin\nWe appreciate the referee’s recommendation of these additional quantum sensing references and believe\ntheir incorporation strengthens the context for and content of this work. We have drawn inspiration from\nthese papers and have updated our introductory references to include them.\n2) Doping level. The authors mention that the doping level of the crystal can be eventually high\n(introduction). However, the concentration used in the experiments is 0.1% corresponding to a collection\nof 10^9 spins and a volume of 2.6 ∙ 10−5 𝑚𝑚3 (Section II). This is giving FWHM linewidth of ≈ 4.8 𝑀𝐻𝑧. This concentration value is not so small and even so large. Could the authors comment on how the linewidth\nis affected by the concentration?\nWe thank the referee for the question. The ODMR lineshape exhibits a distinctive asymmetric profile,\nwhich we addressed in a previous manuscript [1]. The linewidth is primarily governed by hyperfine\ninteractions with proximal 1H nuclear spins in the pentacene aromatic rings [1] . While increased linewidth\nat higher concentrations is expected due to inter-electron interactions [2], the behavior is more nuanced.\nSeveral competing processes—such as singlet fission and triplet-triplet annihilation—contribute to the\ndynamics and are typically described using a Jablonski diagram that captures the relevant transition rates\n(see Ref. [3] for further discussion).\nWe also note a synthetic limitation in the achievable doping concentration for the p-terphenyl host, where\nit is difficult to exceed ~3% pentacene loading. In alternative host materials, however, higher concentrations\nmay be feasible. We plan to explore these possibilities in future work and have expanded the discussion\nand references in the revised manuscript to clarify these\npoints.\nAnd on how much the concentration could be, in principle,\nincreased or further decreased?\nCrystal preparation constrains the theoretical maximum and\nminimum pentacene concentrations we can achieve.\nExperimentally, we have prepared doped crystals with\nconcentrations up to 0.3% by mass (Fig. 1). Although\nhigher concentrations are in principle possible for this\nsystem, a comprehensive study of the effects of such high\nconcentrations has not yet been conducted (to the best of\nour knowledge), excluding the results described in [3] on\nthin films. Pentacene may likely have increased solubility\nin the crystal melt when doped into different host systems,\nFigure 1: PDP crystals synthesized with\nresulting in a higher concentration in the final crystal. We\nvarying pentacene concentrations. From left\nare actively investigating the use of other hosts to produce\nto right: 0.3%, 0.1%, and 0.05% pentacene\ndifferent solid solution crystalline materials.\ndoping, highlighting precise control over\nLower pentacene concentrations are achieved by diluting\ndopant levels and the ability to tune\nthe starting concentration of the pentacene/p-terphenyl\nconcentration across a broad range.\npowder. The lowest concentration we have explored thus far is 0.025% by mass, but we anticipate that\nlower concentrations can be achieved.\n3) Sample size. The sample shown in Fig. 1.c has a remarkably large size for a single crystal. However, the\nfraction of the volume used for experiments is only 2.6 ∙ 10−5 𝑚𝑚3 which means that most of the volume\navailable is effectively not necessary and not used during experiments. The same holds by considering the\nsample volume reported in Supplementary Material (Experimental Setup section). Which are the factors\nlimiting the use of a larger sample volume?\nWe thank the referee for the thoughtful question. Our proof-of-concept experiments were deliberately\nconducted on a relatively small ensemble of spins, guided by two key motivations. First, our primary goal\nwas to characterize the intrinsic sensitivity of the PDP material to environmental variables—specifically,\nthe shifts in ODMR frequency with temperature and pressure, denoted ∂f/∂T and ∂f/∂P. These parameters\nreflect the material’s inherent responsiveness to thermal and mechanical stimuli and are largely independent\nof experimental conditions such as photon collection efficiency or instrumentation. Our measurements\nindicate that these shifts are significantly larger than those observed in NV centers in diamond.\nSecond, we chose to demonstrate these effects using cw laser excitation, aiming for practical deployment.\nSince PDP crystals are inexpensive to synthesize, we sought to show that both the materials and the\nmeasurement infrastructure can remain low-cost.\nUsing larger spin ensembles would indeed improve absolute sensitivity. Prior work in dynamic nuclear\npolarization (DNP) [4,5] and pentacene-based masers [6] has leveraged large para-terphenyl and\nnaphthalene crystals for this purpose. However, these experiments typically require pulsed laser excitation\nto illuminate larger volumes and must consider depth-dependent absorption (Ref. [7] identifies ~589 nm as\noptimal). Adapting such strategies could yield substantial sensitivity gains for bulk pressure and\ntemperature sensing.\nHow does the RF/MW field inhomogeneity affect the FWHM linewidth?\nThe referee raises a valid concern regarding RF inhomogeneity. RF/MW field inhomogeneity will increase\nthe experimental FWHM linewidths. In the setup used in this work, however, the RF field is effectively\nuniform across the probed spin ensemble. This is achieved through the use of a solenoidal coil geometry,\nwhich confines the detection region well within the zone of RF homogeneity. Additionally, the design of\nmicrowave coils or resonators with large homogeneous volumes is well established—even for centimeter-\nscale crystals—as demonstrated in DNP and maser experiments. Instead, the dominant contribution to the\nobserved linewidth is from hyperfine interactions with protons in the host material. This broadening can be\nreduced by deuteration [8].\n4) Cost reported for sample in Fig. 1.c. The cost for the large crystal is estimated in 2.25 US dollars\naccounting only for materials. I really appreciate the comparison in terms of cost of production between a\nsynthetic crystal and an artificial diamond (such as NV centers). However, in my opinion the comparison\ncould be further extended and detailed. Possible points of interest for considering the cost might be:\n- artificial diamonds are grown by chemical vapour deposition of by high-pressure high-\ntemperature methods. Nitrogen and vacancies can be then created by ion implantation or neutron irradiation\nfollowed by thermal annealing. This initial difficulty can be overcome considering that there are specialized\ncompanies offering commercial NV centers.\n- molecular spins offer an easier way of fabrication due to chemical synthesis. Here, however, raw\nmaterials with adequate quality and purity might be necessary and specific chemical techniques and chemical\nfacilities for purification or making reactions. The recipe could require several complex steps and could be\nnot so easy to be obtained or optimized at the beginning. The yield of the reaction could be not so high.\nNormalizing the cost over the mass of the product might be misleading as well. An alternative could be to\nnormalize over the density of the sample or on the spin concentration obtained (spins centers per unit of\nvolume). This extended discussion could be added in a dedicated section of the Supplementary Material.\nWe thank the referee for their commendation of our cost comparison between the PDP crystal and NV-\ndiamond materials. Please see the following breakdown for how we arrived at our conclusions from a\nmaterials and preparation angle. We have also updated the Supplemental Information to include a section\non “Cost Analysis” for interested readers. Note that we have updated the discussion to normalize by spin\ndensity, which is a more relevant metric in this case.\nCost Analysis\nHere, we detail how we arrived at the $2.06 materials cost per crystal quoted in the main\nmanuscript. Note that all prices quoted are current as of 4/22/25.\nMaterials Costs\nFor a typical PDP crystal, ≈ 1 mg of pentacene is doped into ≈ 1 g of p-terphenyl. Referencing Sigma\nAldrich prices of $179 for a 100 gram stock bottle of p-terphenyl and $1350 for a 5 gram stock of pentacene,\nthis comes to $2.06 per ≈ 1g crystal sample ($0.00206 per mg or $0.00000249 per ppb pentacene). NV−\ndiamond samples are typically purchased from specialized commercial entities, eliminating the need for in-\nhouse high cost instrumentation for chemical vapor deposition (CVD), high-pressure high-temperature\n(HPHT) growth, and beamline work. A representative ThorLabs-supplied, Element Six-fabricated\ncommercial DNVB1 single crystal NV− diamond sample has 300 ppb NV− concentration and is sold at\n$1542.24 ($97.92 per mg or $5.14 per ppb NV−). The highest concentration DNVB14 diamond sample\nthey supply has a 4.5 ppm NV− concentration, costing $3325.46 ($211.14 per mg or $0.74 per ppb NV−).\nFixed Costs Associated with Growth\np-terphenyl and\npentacene are purified\nFigure 2: Homebuilt apparatus for high-throughput growth\nin-house prior to the\ncrystal growth, so it is of large PDP crystals. Each modular setup—comprising a\nuseful to consider how custom-built furnace and motor assembly—enables the growth\nthis extra purification\nof multiple centimeter-scale PDP crystals within 24 hours. Five\nstep contributes in the\ncost analysis. P-\nsuch devices, designed for parallel operation, are shown.\nterphenyl is purified via\nzone-refinement. The\nsetup we use employs\nnichrome wire, a 24 V\npower supply, glass\ntubing, a mechanical\nshuttling system\n(actuator and motor),\nand a motion control\nprogrammer. The\nprimary costs here are\nfor the power supply,\nmechanical actuator,\nFigure 2: Homebuilt apparatus for high-throughput growth of large PDP\nand motion\ncrystals. Each modular setup—comprising a custom-built furnace and motor\nprogrammer, which\nassembly—enables the growth of multiple centimeter-scale PDP crystals within\ncost $52, ≈$270, and\n24 hours. Five such devices, designed for parallel operation, are shown.\n$46, respectively.\nPentacene is purified via sublimation, accomplished in a home-built horizontal furnace. This setup consists\nof wire, a 24 V power supply, glass tubes, and high purity Argon gas. Presuming excess wire and glass\ntubes remain from the zone refinement setup construction, the primary cost of this step are the Ar gas\ncylinder and the power supply: $66 and $52, respectively.\nBridgman crystal growth is done in a home built furnace which uses wire, a ceramic tube, a 24 V power\nsupply, a mechanical shuttling system, and a motion control programmer. The primary costs here are the\npower supply, shuttling system, and the motion control, $52, ≈$270, and $46 respectively. The total cost,\ninclusive of preparation and crystal growth supplies, is a fixed ≈$900 addition to the overall material price.\nOnce multiple crystals are produced, the additional cost per crystal is just the material cost ≈$2.\nSummary\nFrom a purely materials standpoint, even without normalization, buying the two stock chemicals to make a\nPDP crystal is cheaper than buying the cheapest ThorLabs-supplied Element Six diamond sample ($1529\nvs. $1542). Normalization by mass ($0.00206 per mg PDP vs. $97.92 per mg or $211.14 per mg NV-\ndiamond, depending on the sample) OR by spin density ($0.00000249 per ppb pentacene vs. $5.14 per ppb\nNV− or $0.74 per ppm NV, depending on the sample) further highlights the cost benefits of using PDP\ncrystals, relative to NV centers. The additional cost for the two purification and growth setups is a one-\ntime, initial ≈$900 investment (≈$350 per step) which is still cheaper to produce at scale than commercial\nchemical vapor deposition instrumentation for diamond fabrication. For example, we have developed an\nin-house scale crystal production setup capable of mass-producing samples (Fig. 2). With all sample\nproduction and material costs taken into consideration, we conclude that PDP crystals are a significantly\ncheaper alternative relative to NV− diamonds.\nIt seems that there is a slight broadening of the signals as the temperature is increased from 100 K to 300\nK. However, Fig. 1.D and 1.E suggest the broadening of the lines occurs at low temperature, not at 300 K.\nCan the authors comment on this point?\nWe apologize for the confusion; the 3D visualization was used to make the shift more visually apparent and\nappealing in Fig. 2. However, we now realize it may have a deceiving effect on the eye for panel A. To aid\nin interpreting this data, we unambiguously show the frequency shift as a function of measured temperature\nin Fig. 2B. There is a consistent line broadening with decreasing temperature. \n6) Section III, the change in the spectral frequency 𝑑𝑓⁄𝑑 𝑇 (and its equivalent for pressure sensing 𝑑𝑓⁄𝑑𝑃).\nIt is stated that this quantity is material-specific and independent by the measurement apparatus or light\ncollection efficiency. The temperature (or the pressure) is changed in the environment (cryostat or pressure\ncell) it is a global macroscopic experimental parameter of the whole sample (not a local one). Moreover,\nthe setup it is said to be not optimized for sensitivity and that the collection efficiency affects the measured\nsignal. In my opinion, the sample size (number of spins), the laser power, the RF/MW power can affect the\nabsolute signal measured. So, one might expect 𝑑𝑓⁄𝑑 𝑇 (or 𝑑𝑓⁄𝑑 𝑃 ) to be affected by the setup and\nexperimental conditions as well. Could the authors better clarify this point?\nThe resonance frequency—if measured with sufficient precision—is governed by the intrinsic interaction\nbetween the spin system and its environment (temperature or pressure). Temperature- or pressure-induced\nchanges in the spin Hamiltonian (e.g., via lattice strain, crystal field effects, or spin–phonon coupling) shift\nthe resonant frequency, not the signal amplitude or quality of measurement. In this sense, the slope 𝑑𝑓⁄𝑑𝑇\n(or 𝑑𝑓⁄𝑑𝑃) is expected to be independent of the measurement apparatus under ideal conditions,\nIn this work, laser and RF/MW power were used within their linear regimes, and global\ntemperature/pressure changes were well-controlled across the sample during measurement to minimize or\neliminate drift-associated changes to the resonance frequency. To better clarify this point, we have revised\nthe Table I caption in the main paper where this was stated to read:\n\"Slopes of ODMR frequency variations 𝑑𝑓⁄𝑑𝑇 and 𝑑𝑓⁄𝑑𝑃 are material properties and reflect\nthe intrinsic spin–environment interactions in the host material, provided that extrinsic\nperturbations (e.g., local heating, power broadening) are avoided. The signal strength and\ndetection sensitivity (𝜂T, 𝜂P) are affected by experimental parameters such as laser power,\nsample size, and RF/MW conditions.\"\n7) End of the Section III. It is mentioned that the sensitivity 𝜂 = 𝜎√𝜏/ 𝑑𝑇 depends on many experimental\nparameters, including number of spins and collection efficiency so, it ultimately depends by the apparatus\nand experimental conditions. I agree with the definition of sensitivity used by the authors in the manuscript\n(which includes also the change in the spectral frequency). In my opinion introducing the noise floor level\nand the integration time with the mentioned definition of sensitivity can give a better comparison among\ndifferent experiments and, eventually, setups and samples. This is because it can be a way to normalize the\nchange in the spectral frequency over different experiments and apparatus. Could the authors comment on\nthis point?\nWe agree that sensitivity—defined as 𝜂 = 𝜎√𝜏 / (𝑑𝑓/𝑑𝑇)—is not solely a material property but is strongly\ninfluenced by the experimental setup, including factors such as collection efficiency, number of spins, and\nnoise characteristics. Indeed, the inclusion of the noise floor σ and integration time τ in the definitions of\ntemperature and pressure sensitivity we provided gives a complete and practical description of sensor\nperformance. This form allows for a direct comparison between different experiments and platforms\nthrough normalizing by measurable, apparatus-dependent parameters.\nWe have updated the manuscript to explicitly state this:\n“This definition incorporates both intrinsic properties (e.g., spectral shift) and extrinsic factors\n(e.g., noise level and integration time), and thus serves as a comprehensive figure of merit for\ncomparing different experimental setups and material systems.”\nWe have also updated the “Sensitivity Measurement” section of the SI to now report the estimated values\nof σ and τ for our measurements, and we emphasize that optimization of these parameters—along with\nimprovements in collection efficiency and spin ensemble size—could significantly improve the overall\nsensitivity.\nIn my opinion the reader would benefit from having more details about the available experimental\nparameters …. This could be part of an extended Table I in Supplementary Material.\nWe note that an apples-to-apples comparison between sensor platforms is challenging, given that the papers\nreferenced for other sensor platforms did not always provide all the experimental details mentioned. With\nthis in mind, we have expanded the platform comparison table in the Supplementary Information of the\npaper to include laser power, collection efficiency, and spin density (ppm) as reported. Parameters not\nexplicitly reported were calculated to give reasonable estimates for purposes of evaluation.\n9) Protocol used for quantum sensing. The manuscript is citing a preprint by almost the same group of\nauthors (Ref. 34) in which quantum sensing of magnetic field is experimentally realized with a similar\npentacene-doped crystal and using again an ODMR approach. The sensing protocol in Ref. 34 seems to be\nfully pulsed-wave in the sense that both optical pulses and RF/MW pulses are used, while in the present\nmanuscript the optical excitation is given in continuous wave. Could the authors explain why they chose to\nuse a continuous wave protocol instead of a fully pulsed-wave one? Is there any advantage in running the\nsensor for pressure or temperature this way? In my opinion, running the sensor in pulsed-wave and\nexploiting its quantum coherence (as type II sensor according to Ref. [1]) would give more convincing\nevidence for a quantum sensing protocol (not only a larger contrast).\nA CW protocol was employed instead of the pulsed protocol used previously (Ref 3), because we designed\nthe experiments with an eye towards low-cost applications. A fully CW protocol facilitates the use of\ncommercial lasers, which can be obtained in cheap, compact form factors. For example, the laser powers\nemployed in these measurements are ~16 mW, a range easily covered by commercially available 532nm\ndiode lasers. Electronics in the 1300-1500 MHz microwave frequency ranges employed are already\ncommercially available, and the material itself costs only ~$2 to make (see response to Referee 1 Question\n4).\nIn total, the cost-effectiveness of individual technological components used here present a readily\nscalable pressure / temperature sensing platform. As noted previously, we emphasize that even with a\nsimple CW scheme, we achieve record pressure sensitivities. The high sensitivity is intrinsic to the material\nused and is independent of the high SNR a pulsed protocol would provide a more commercially relevant\nresult.\n10) Experimental setup. The experimental setup is described in detail. However, there is no information on\nthe optical power reaching the sample or on the RF/MW ones.\nThe reader might benefit in such additional technical information about the protocols and on how the\nexcitations and given and which is their timing or duration (see also the introduction and point 9 above).\nAdding details about the role of the lock-in and on how the contrast is extracted from experimental data\nmight help the audience which is not familiar with ODMR. This information could be added in\nSupplementary Material.\nWe thank the referee for pointing out where the description of our experimental setup could benefit from\nadditional detail. We discuss the relevant experimental parameters here and have added information to the\nSI. For all experiments, we can only report the laser power at the optical window (either of the cryostat or\nthe pressure chamber) because the laser power meter head is too large to fit inside the cryostat or pressure\nchamber itself. The laser power reaching the optical window was 110 mW and the MW power fed through\nthe single loop resonator was ~ 1 W for pressure sensing experiments and ~0.3 W for temperature sensing\nexperiments. We have updated the SI with this experimental information.\nThe PL is collected using convex lenses and converted into an electrical signal using an Avalanche\nPhotodiode (APD) module (Hamamatsu, C12703). The electrical signal is demodulated with a lock-in\namplifier (SRS model SR830 DSP), whose reference signal modulates the RF (ON/OFF) at 1 kHz. ODMR\ncontrast is defined as the change in the PL signal when the RF power is ON and OFF, divided by the PL\nsignal when the RF is OFF. We have updated the SI with this experimental information.\nFor more detail about the ODMR measurements, Figure 1 has been updated with the cw-sensing protocol\nemployed and the SI was updated with a brief description of how contrast is calculated in the “Contrast\nMeasurement” section. The same detection scheme was used for all experiments.\n11) It could be helpful to add a guide for eyes also in Fig. 3.A and 3.B, in a way similar to what was done\nin Fig. 2.A and 2.B.\nWe appreciate the referee’s suggestion and have added a guide to the eye for clarity in Fig. 3A and 3B.\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 2\nIn the submitted manuscript, the authors report on the utility of pentacene-doped in p-terphenyl host lattice\nas pressure and temperature sensor. The main idea behind the study is the leveraging of flexible nature of\nmolecular crystals, relative to the well-investigated diamond lattice hosting NV centres, as a better sensor\nmaterial. The manuscript is well-structured and fundamental concepts are eloquently presented. The authors\nneed to address the following comments to determine the suitability of the script for publication in Nature\nCommunications.\nWe sincerely thank the reviewer for their thoughtful evaluation and positive remarks on the structure,\neloquence, and clarity of our manuscript. We appreciate the acknowledgment of our study's central idea—\nutilizing the flexible nature of molecular crystals, specifically pentacene-doped p-terphenyl, as a promising\nalternative to rigid diamond lattices for pressure and temperature sensing. We have carefully considered all\nthe reviewer’s comments and addressed them point by point in the revised manuscript and the\naccompanying response document.\nTitle: The term organic crystals is rather general. I think the title would be more informative, if the authors\nuse “pentacene-doped p-terphenyl single crystals” instead of organic crystals.\nWe agree that specifying the material used can make the title more informative and precise. Accordingly,\nwe have revised the title to: “High sensitivity pressure and temperature quantum sensing in pentacene-\ndoped p-terphenyl single crystals”\nAbstract: Please mention temperature and pressure ranges studied.\nWe have revised the abstract to include the specific temperature and pressure ranges studied in our\nexperiments for improved clarity and context for the reader.\nI. Introduction\n1. The authors cite references 28 and 29 as dealing with rare-earth ions. While it’s true 29 deals with rare-\nearth ion (Eu3+), the reference 28 deals with Cr4+ molecules, a transition metal system. Please correct this\ndiscrepancy by rewriting the sentence. There is a typo: “utilizing are-earth ions”\nWe apologize for the typo and have corrected this line in the introduction to “utilizing rare-earth or\ntransition-metal ions”.\n2. What does the authors mean by tunable sensor placement in three-dimensions? Please elaborate.\nWe apologize if our phrasing caused any confusion, and we clarify here. In the phrase “tunable sensor\nplacement in three-dimensions”, we are referring to molecular quantum sensors used as linkers in metal-\norganic frameworks (MOFs) [9]. These crystalline porous materials are highly modular in their\nconstruction, so changing the identity of the linker or the metal ion / metal cluster node can adjust the\nsensor’s spatial configuration through altering the MOF structure [10]. For added clarity in the introduction,\nwe have changed the wording in the following text:\n“These systems offer advantages stemming from bottom-up synthesis, tunable sensor placement in\nthree-dimensions via integration into porous materials and molecular-level control over sensor\nproperties”.\n3. For easy referencing, the authors can give values for the size of the single crystals and doping levels of\nsensor molecule in a host.\nWe have included the single crystal size and doping levels in the following phrase in the introduction:\n“Additionally, the material can be grown into large single crystals (3 cm) with high doping levels (~1000\nppm)”.\nII. System and principle\nDoes the doping concentration affect the sensing capability of the system?\nAdditional mechanisms set in at higher doping concentrations which make it challenging to unambiguously\npredict sensing capabilities at higher doping levels. We discuss contributing factors below.\nThe doping level of 0.1% (w/w) (~827 ppm) pentacene achieved here is high, compared to the record\nin similar quantum sensing materials. For example, semiconductor defects like the NV- center have\nachieved up to ~16 ppm [11]. As discussed in our response to Referee 1 Question 2, we have grown crystals\nwith dopings up to 0.3% (w/w) thus far (see Fig. 1 of that same response), with the upper % doping limit\nset by pentacene’s solubility in the p-terphenyl melt. Pentacene may have a higher solubility in other host\nmaterials.\nIn our current samples, ODMR linewidths are principally broadened by hyperfine coupling to proximal\nnuclear spins. Since the pentacene is dilutely incorporated into the lattice (~1:1209 pentacene:p-terphenyl\nmolecules), we expect that electron-electron dipolar interactions contribute minimally to peak broadening,\nwhich would decrease sensing capability.\nAt high pentacene concentrations in PDP thin films, previous work demonstrated the onset of other\ntriplet pathways, such as singlet fission and quintet state formation [3]. Furthermore, as the inter-pentacene\ndistance decreases, we may expect a greater relaxation contribution from dipolar interactions.\nIn summary, the high concentration molecular quantum sensor regime is an exciting but not yet well\nexplored parameter space. We expect that striking the balance between high sensor concentration and\nminimal feeding of other triplet pathways to be the optimal triplet molecular quantum sensor profile.\nThe figure 1E is labelled with 79 K, while the text says 77 K.\nWe thank the referee for pointing out this typo. The correct temperature is 79 K, and the manuscript has\nbeen updated accordingly.\nPlease show the TXZ linewidth at 79 K (77 K?)\nFigure 1 has been updated to show the TXZ linewidth, 8.9 MHz.\nIII. Triplet ODMR variation with temperature\nIn Figure 2C, the authors can add temperatures for easy referencing of temperature-dependent phase\nchange.\nFigure 2C has been updated with the measured temperature corresponding to each para-terphenyl crystal\nstructure.\nSince pentacene performs a useful function, the authors can write “sensitive reporters” instead of “sensitive\nspectators”\nWe have incorporated the suggested change in the manuscript.\nIn figure 1D and E, the ODMR frequencies of XY and XZ transitions increase with decreasing temperature.\nHowever, in figure 2A, for XY, the trend seems opposite. I am a bit confused how to interpret the data\npresented in the figures.\nThere was a mistake made in Illustrator during the figure preparation, we sincerely apologize for this error.\nThe correct trend is that the transition frequency decreases with decreasing temperature for the YZ and XZ\ntransitions and increases with decreasing temperature for the XY transition, as shown in Figure 2B. We\nthank the referee for noticing this error. We have corrected the figure in the revised manuscript.\nThe attribution of drop occurring after 290 K to the crystals being close to the melting point (486 K, as\nmentioned by the authors) is rather tentative. The issue is compounded by almost 200 K difference. Could\nthe authors provide a more logical explanation?\nWe thank the referee for their comment. In general, the polarization lifetime decreases with increasing\ntemperature due to the Boltzmann distribution. Also, triplet population and depopulation rates will change\nwith increasing temperature, likely shortening the triplet state lifetime. This may also be related to signal\nloss from exciton delocalization at elevated temperatures; exciton hopping barriers are typically in the range\nof 25 meV. These are more logical explanations for why contrast decreases in this regime of the plot, rather\nthan approaching the melting point, which is much farther away in temperature. We have updated the\nmanuscript accordingly to read the following:\n“Another drop occurs after the\nplateau past 290 K, likely due to\nexciton delocalization at elevated\ntemperatures and increasing\ntemperature decreasing the\npolarization lifetime and changing\nthe intersystem crossing rates and\ntriplet depopulation rates.”\nApart from the frequency shift with\nrespect to temperature, the intensity\nof the ODMR transitions seems to\nchange with temperature. Could this\nintensity variation used to sense\nFigure 3: Variation of photoluminescence intensity with\ntemperature, more like\ntemperature.\nluminescence thermometry\n(https://doi.org/10.1002/adma.202302749) reported for luminescent molecular and solid-state systems?\nIt would be interesting, if the authors make a comparative study between intensity and frequency variation\nwith respect to temperature.\nWe thank the reviewer for their suggestions for developing this system as a multimodal sensor platform.\nAs the intersystem crossing (ISC) rate decreases with decreasing temperature [12], a higher PL is observed\nat lower temperatures (see Fig. 3). This is because most of the pentacene molecules undergo spontaneous\nemission from the excited singlet state to the ground singlet state, rather than undergoing ISC into the triplet\nstate.\nIn Fig. 3, we have plotted the PL vs. temperature graph below and estimated the relative thermal\nsensitivity, Sr(T)=0.11%, using the expression:\nSr(T) = (1 / PL(T)) × (dPL(T) / dT) × 100% = 0.11%.\nThe deviations from linearity are not currently completely understood. We are continuing to explore these\ndeviations and the potential causes, including that the response may simply be nonlinear. While there is not\na large PL variation with temperature, it is an interesting angle that we will explore in the future.\nIV. Triplet ODMR variation with pressure\nWhy the authors chose to study Tyz and Txz transitions? What is the rationale behind leaving out the Txy\ntransition?\nInterestingly, not all pentacene triplet transitions demonstrate the same pressure sensitivity. In particular,\nthe T_XY transition is not as sensitive to pressure over the applied ranges studied as the other two\ntransitions, T_YZ and T_XZ. We have included the plots of the T_XY transition frequency’s variation with\npressure below (see Fig. 4) and in the SI, as we did not have space to include it in the main paper.\nAdditionally, we have updated the following line in the manuscript to make this point clearer:\n“Fig. 3A-B presents\nrepresentative ODMR\ntraces for the TYZ and\nTXZ transitions only,\nsince the T_XY transition\nis not as sensitive to\npressure over the applied\nranges studied (see SI\nFigure 4: Frequency variation of the Txy transition with applied\nFig. 4).”\npressure.\nVI. Conclusions\nI do agree with the authors that the studied system is interesting. However, I have difficulties accepting the\nsystem as a compelling pressure and temperature sensor.\nIn our humble opinion, the pentacene-doped para-terphenyl (PDP) system shows strong potential as a\npressure and temperature sensor. Its high sensitivity coupled with low experimental costs and scalable\nproduction make it well-suited for practical applications, as detailed below.\nAs discussed in responses to Referee 1 Questions 4 and 9, the material costs to set up scale crystal\nproduction are modest. Each crystal costs approximately $2 with a one-time infrastructure cost of $900.\nThe equipment needed to run experiments, a cw 532 nm laser and microwave electronics, are commercially\navailable. Aside from the initial investment in crystal production and acquiring equipment, the barrier to\nadopting this technology is low.\nWe envision this system evolving into a deployable quantum sensor, akin to existing NV-diamond\nmagnetometers [13]. Its low component cost and compact footprint support the development of a portable\nsensing platform. Both single crystal and thin film PDP form factors can be evaluated to determine which\nis better suited for such applications.\nThe PDP system’s 1–2 bar optimal pressure range aligns with key use cases, including tire pressure\nmonitoring, hydraulic fluid sensing, and altimetry—each requiring reliable detection of small pressure\nchanges (see Page 13 for a more detailed discussion). The high sensitivity demonstrated by this organic\ncrystal also points to a broader class of organic molecule-based pressure sensors. Since pressure sensitivity\nis largely governed by the Young’s modulus of the host lattice—which can be higher in organic molecular\nsystems than in semiconductor defect systems—we anticipate further development of such sensors. Organic\nmolecules spatially arranged via incorporation into MOFs offer a promising direction for expanding this\nmaterial class.\nThe same applies to the “elimination of reliance on electronic defects…” In my humble opinion, the\nstatements are far-fetched and require rewriting.\nThe referee’s point about the elimination of semiconductor defect materials is well taken, and we have\nrephrased the discussion and outlook phrase to highlight molecular quantum sensors as a complementary\nmaterial platform to defects in semiconductors with the following language:\n“This approach does not rely on electronic defects in semiconductor lattices and opens new design\npossibilities through chemical synthesis.”\nCould the authors discuss how the chemical design strategies can be leveraged to improve the sensitivity\nof the crystalline system discussed in the manuscript? For example, could deuteration enhance the optical\nproperties with the consequent effect on sensing capability?\nTwo chemical design strategies that can improve the sensitivity of the crystalline system employed are\ndeuteration of the host pentacene molecule and utilization of a pentacene derivative, 6,13-diazapentacene.\nAs demonstrated in the X-band EPR study by Sloop et. al. [14], deuteration of the pentacene host increases\nthe triplet state lifetimes of the T and T states (the T state is relatively unchanged) and slightly improves\n+1 -1 0\nthe polarization lifetime for the T to T transition and T to T transition (T to T is slightly worsened).\n0 +1 -1 +1 0 -1\nWhile the population rates of the 1 and -1 sublevels are slightly decreased relative to fully protonated\npentacene, the difference in the population rates is improved, which would increase polarization in this\ntransition (Table 1). We anticipate that the cumulative effect of improvement in triplet state lifetimes,\npolarization lifetimes, and triplet population rates would improve the polarization and enhance the SNR of\nthe measurements.\nPopulation rate Spin-lattice decay Decay rate\nrate(a)\nPentacene-d₁₆ P₁ = 0.4 ± 0.05 W₁ = 1.77 × 10⁴ k₁ = 7.52 × 10³\nP = 016 ± 0.02 W₂ = 2.86 × 10⁴ k₀ = 10³\nPentacene-h₁₄ P₁ = 0.44 ± 0.05 W₁ = 1.85 × 10⁴ k₁ = 1.52 × 10⁴\nP₀ = 0.09 ± 0.02 W₂ = 2.63 × 10⁴ k₀ = 10³\nP₋₁ = 0.47 ± 0.05 W₃= 0.658 × 10⁴ k₋₁ = 1.39 × 10⁴\nTable 1: Triplet state parameter comparison between deuterated and protonated pentacene doped in para-\nterphenyl. Reproduced from Ref 14.\n\\⁽ᵃ⁾ W₁ is the rate for |0⟩ ↔ |+1⟩ transition, W₂ for |0⟩ ↔ |-1⟩, and W₃ for |-1⟩ ↔ |+1⟩.\nThe best fit of the kinetic parameters at 25°C (s⁻¹). The estimated errors for all the parameters except k₀ are\n±10%. The estimated error for k₀ is ±50%.\nSimilarly, 6,13-diazapentacene-doped para-terphenyl has recently been shown as a high contrast quantum\nsensing material (Fig. 5) for magnetometry applications [15]. Since the primary temperature and pressure\nsensitivity properties we show here result from the p-terphenyl lattice phase transitions and compressibility,\nwe anticipate pressure and temperature sensing would be possible with this doped crystal as well, again\nwith higher contrast and improved measurement SNR.\nLastly, pentacene or its chemical-derivatives could be incorporated as a building block into porous\ncrystalline materials [16],\nsuch as metal-organic\nframeworks, for tunable\nsensor placement in 3D\nporous materials [17].\nA minor remark:\nThere is\nalways a space between value\nand unit: for example, please\ncorrect 77-330K in the\nintroduction, in the caption of\nFigure 1, and other parts of the\nmanuscript.\nWe thank the reviewer for this\nFigure 5: Chemically tuning the ODMR contrast (from Ref. 14)\nremark. We have carefully\nrevised the manuscript and\nensured that a space is\nincluded between numerical values and units throughout the text, including in the Introduction, Fig. 1\ncaption, and all other relevant sections.\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 3\nSingh et al. described a quantum sensing system based on pentacene in p-terphenyl crystals, which\ndemonstrates high sensitivity to temperature and pressure through shifts observed in optically detected\nmagnetic resonance (ODMR) spectra. While the study presents the novelty of using ODMR to measure\nthese parameters, it is important to note that several key aspects of the work are already well documented\nin the literature. These include the use of pentacene triplet spin states for quantum sensing, the application\nof ODMR (and EDMR) to address these spin states, and the sensitivity of pentacene triplet states to both\ntemperature, including phase changes, and pressure (e.g., ref 42, https://doi.org/10.1021/jp070251v). Given\nthat pentacene triplets are a well-established molecular platform, it is not surprising that the authors were\nable to optically detect spectral shifts and utilize them to sense these parameters. Nevertheless, I recognize\nthat the use of emission-based detection in this context is a novel contribution, and I could potentially\nsupport the acceptance of the manuscript.\nWe thank the reviewer for their thoughtful comments and for recognizing the novelty of our room\ntemperature, emission-based detection approach for quantum sensing using pentacene in p-terphenyl\ncrystals.\nThe pressure ranges accessible with the pentacene-doped para-terphenyl material enable operation in a\ncomplementary pressure range to NV- diamond-based sensors, a benchmark quantum pressure sensing\nmaterial. The organic p-terphenyl crystal lattice is softer than that of the more rigid diamond-based systems.\nMechanical softness enables the lattice to respond more sensitively to lower pressure variations, facilitating\noperation in the low-pressure regime where diamond NV-center sensors are less effective or overly stiff.\nThis expands the application range of quantum sensing technologies.\nWe have added the reference mentioned to our discussion of phase transitions in this material.\nHowever, I would like the authors to address how they envision using this system as a sensor in real-world\napplications. Specifically:\n● What types of target environments would this sensor be used for?\n● Why are such capabilities necessary or advantageous in those contexts?\nWe thank the referee for raising this point. We envision a broad range of applications for PDP crystals\nacross diverse domains. While our discussion here is focused more on pressure/strain sensing, similarly\nwide applications can be envisioned for temperature sensing.\nStrain-mediated spin actuation: One particularly compelling application lies in the strain-mediated\ncontrol of spin systems. Prior studies have shown that electronic spins, such as those in nitrogen-vacancy\n(NV) centers in diamond, can be coherently actuated using strain fields, including standing-wave strain\npatterns produced by H-bar resonators [18] or through diamond cantilever devices [19,20]. This spin-strain\nactuation has evolved into a major research area, including efforts to control spins using single\nphonons [21]. However, the\nimplementation of these ideas in diamond\nhas been hampered by the material’s\ninherently low strain sensitivity. Typically,\nstress levels on the order of MPa are\nrequired to achieve meaningful spin\nactuation [18], necessitating either high-\nstrain cantilevers or advanced\nnanofabrication techniques directly in\nFigure 6: Preliminary work showing pentacene doped\ndiamond—both of which present\ncrystals grown as needle like structures.\nchallenges.\nIn contrast, PDP crystals offer an attractive alternative. These crystals are significantly easier to fabricate.\nIn new unpublished work, we have shown that pentacene-based crystals can be grown in needle-like\nmorphologies, which are directly amenable to use as cantilevers (see Fig. 6). The inherent strain sensitivity\nroughly three orders of magnitude higher than that of diamond makes it possible to actuate spins at\nsubstantially lower strain and power thresholds.\nOptical pressure and strain sensing devices: More broadly, we envision PDP crystals as general-purpose\npressure and strain sensors potentially surpassing the capabilities of classical devices (e.g. strain gauges).\nThese sensors may find applications in contexts such as pitot tubes and altimeters. Furthermore, PDP-based\nsensors may enable measurements in contexts where traditional strain gauges are ineffective—for example,\nin mapping high-resolution strain distributions within heterogeneous materials or small-scale structures.\nFrom an engineering perspective, these crystals are highly compatible with low-cost diode laser systems\nand fiber-based optics. This compatibility paves the way for compact, integrated, and scalable pressure\nsensing platforms, akin to recent fiber-based magnetometers demonstrated in Ref. [13].\nFunctional materials via additive manufacturing: We foresee exciting directions in the development of\nfunctional materials by incorporating pentacene or its derivatives into polymers or 3D-printed structures.\nThese composite materials would have built-in optical readout capabilities for strain, pressure, or\ntemperature, accessible simply through laser illumination. We have previously demonstrated a similar\napproach with NV centers in diamond [16,22]: by embedding NV-nanodiamonds into 3D printing filament,\nwe fabricated intricate structures via two-photon polymerization (TPP) with spatially distributed sensing\ncapability.\nFig. 7 illustrates one such porous gyroid structure, where nanodiamonds (seen as red fluorescence) line the\ninterior pore walls. (Here, green autofluorescence arises from the host resin.) We envision analogous\nstructures incorporating PDP nanocrystals, which would offer the added benefits of simpler processing,\nenhanced sensitivity, and the potential for full-field, in-situ strain mapping. Such capabilities could greatly\nbenefit the design of topologically inspired metamaterials and strain-resilient architectures—areas where\ncurrent in-situ strain measurement techniques remain limited. We also highlight relevant work by Carlos\nPortela’s group at MIT [23], where optical\nspectroscopy was used to map strain fields\nin complex 3D-printed structures. In\ncomparison, PDP-based approaches offer\na potentially simpler, built-in readout\nmechanism with higher sensitivity.\nThin-film strain sensors and acoustic\napplications: Pentacene-based thin films,\npatterned directly onto surfaces, represent\nanother promising platform for strain\nsensing. Optical interrogation of these\nFigure 7: Nanodiamond (ND) quantum sensors in 3D\nfilms could allow for spatially resolved\nstructures assembled via TPP. (A) SEM of diamond\nstrain mapping across a substrate.\nporous structures in a “gyroid” cross section. (B) Zoomed\nApplications may include acoustic or\nconfocal image showing ND in the internal walls. Red\nvibrational sensing [24], where such films\nfluorescence is from NDs while green is autofluorescence\nserve as highly responsive coatings that\nfrom the resin.\ntransduce surface deformations—such as\nthose from sound waves—into measurable optical signals.\nBottom-up engineered nanomaterials: On the nanoscale, we envision using pentacene molecules as\nprototypes of modular building blocks in the construction of mechanically responsive materials—\nparticularly in metal-organic frameworks (MOFs) [25]. The high strain sensitivity of PDPs as we\ndemonstrated in this work, stems from their soft mechanical properties, including a low Young’s modulus.\nIn MOF-like systems, one could chemically tune both the mechanical response by varying the internal pore\nstructure, linker rigidity, and other design parameters. This opens a powerful avenue for bottom-up design\nof smart materials with customizable strain sensitivity, expanding the toolbox beyond what is possible with\nconventional semiconductors or defect centers.\nBiological sensing applications: Finally, we see significant opportunities for PDP nanocrystals in\nbiological contexts. These crystals can be synthesized in nanocrystalline form and functionalized for\nincorporation into living systems. Recent work by Ishiwata and coworkers [26] demonstrated successful\nintegration of such nanocrystals into cells, with low ODMR heterogeneity—thanks to less onerous\nrequirements for mechanical ball milling.\nOnce incorporated, these crystals could serve as intracellular strain reporters. For example, forces applied\nto cells—via optical tweezers or during migration—could be monitored through the embedded PDP\nnanocrystals, enabling studies of cell mechanics, viscoelasticity, and intracellular rheology [27,28]. We are\nalso exploring similar applications in plant systems. In unpublished work from our group (Fig. 8), diamond\nnanoparticles embedded in plant roots yielded ODMR readouts from different regions of the rhizosphere.\nWe believe similar experiments with PDP nanocrystals are not only feasible but potentially advantageous,\nenabling detection of mechanical stress in root tissues in response to environmental stimuli such as drought\nor changes in soil composition. These measurements could shed new light on how mechanical cues\ninfluence plant development.\nIn summary, PDP crystals,\nwith their superior strain\nsensitivity, offer a\ncompelling platform for a\ndiverse range of pressure\nand strain sensing\napplications.\nThe performance criteria\nlisted in Table 1 have\nlimited significance if they\ncannot be realized under\npractical conditions… For\nFigure 8: Nanodiamond incorporated into different parts of a root of example, the authors\na living plant and corresponding ODMR signals (unpublished). highlight the phase\ntransition region values for\ndf/dT at 193 K to demonstrate a significantly larger sensitivity than NV centers. However, what is the\npractical relevance of this temperature in real-world sensing applications?\nWe refer to the more detailed response above. Regarding the practical relevance of sensitivity benchmarks\nlike df/dT at 193 K, we highlighted this value to illustrate the intrinsic potential of the molecular system.\nWhile 193 K may not directly correspond to application-relevant temperatures, it reflects the upper limit of\nachievable sensitivity and highlights physical mechanisms that can be tuned to improve performance at\nroom temperature and beyond—a direction we are actively pursuing.\nDFT calculations also suggest that picometer-scale changes are detectable by the molecular orbitals, even\noutside the phase transition region. In other words, any event producing orbital-level changes at that scale\nwould be detectable, regardless of proximity to a phase transition. We have edited the discussion section as\nfollows:\n“This also suggests new quantum sensor form factors, including thin-films, 3D printed materials,\nand nanoparticles, possibly down to the single-molecule level. The all-optical nature of our\ndetection scheme offers a non-invasive route for local sensing, eliminating the need for physical\ncontact or electrical interfaces for readout and anticipating single cell-deployable molecular\ntemperature and strain sensing tags.”\nA similar concern applies to pressure measurements—what is the significance of detecting variations in the\n1–2 bar range? Without clear justification for these conditions, the claimed advantages of the pentacene\nsystem may not translate into meaningful practical benefits, and the presented results do not carry\nsignificant weight or novelty.\nWe refer to the more detailed answer provided above on potential applications. Pressure variations in the\nnarrow 1–2 bar range are highly relevant in biological and microfluidic contexts, such as monitoring\nchanges in osmotic pressure or intracellular vesicle dynamics [27]. When deployed as nanoparticles, PDP\nmolecular crystal-based quantum sensors can be used for additively manufactured, bottom-up engineered\nquantum sensing materials [16] or functional metamaterials [23]. If PDP nanoparticles are surface\nfunctionalized for biological-compatibility [26], then they can be used for in-cell sensing of small, but\nbiologically meaningful, variations in pressure and temperature.\nOverall, the methodology and data presented appear reasonably sound. I would recommend addressing\nthese points to strengthen the paper's relevance and provide a clearer vision for its potential applications.\nWe thank the reviewer for their favorable comments on our methodology and the quality of our data and\nfor their useful feedback. We hope that the revised version of the manuscript now clearly outlines the scope\nof applications for this system and the significance and novelty of the results.\nMinor comments:\np2: “The PDP crystal in Fig. 1C requires only $2.25 in materials cost, representing a ∼70,000-fold reduction\nin mass-normalized cost compared to NV-diamond.” This requires either citation or some support for the\nnumbers\nReferee 1 had a similar comment related to how we arrived at the stated crystal materials cost, so we refer\nthe reviewer to our answer to Referee 1’s Question #4 and the associated new section of the SI.\np2: “Fig. 1D the case for RT and Earth’s field.” Missing is?\nWe thank the referee for catching this typo and have updated the manuscript accordingly.\nREFERENCES\n[1] H. Singh, N. D’Souza, K. Zhong, E. Druga, J. Oshiro, B. Blankenship, R. Montis, J. A. Reimer, J. D.\nBreeze, and A. 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PC126570A."}, "author_response": "MANUSCRIPT NCOMMS-24-69634:\n“High sensitivity pressure and temperature quantum sensing in organic crystals”\nReferee Comments are in Black; Authors’ Response are in Blue\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 1\nThe data presented are very clear, accurate and, overall, of good quality.\nWe thank the referee for their praise for the clarity, accuracy, and overall quality of the manuscript!\nThe comparison with the pressure and temperature sensing performed over different spin centers (such as\n– but not limited to - Nitrogen-Vacancy centers) allows us to appreciate the potential of molecular spins as\nsensors.\nWe are glad that the referee found the tabulated comparison between different pressure and temperature\nsensing platforms useful.\nNotably and very interestingly, the final part of the manuscript contains DFT results which support the data\nand suggest the possible origin (at molecular orbital level) of the advantage of molecular spins for sensing\npressure and temperature if compared to other magnetic spin impurities.\nWe thank the referee for appreciating the valuable theoretical underpinnings in our argument.\nIn my opinion the manuscript, in its actual version, is for sure reporting a molecular-based pressure and\ntemperature quantum sensor, highlighting potential advantages with respect to other paramagnetic spin\ndefects or impurities and a possible explanation about the origin of such advantages.\nWe thank the referee for their favorable assessment of the manuscript, the potential of the molecular\npressure and temperature sensing platform presented, and fundamental work to understand the system’s\nproperties.\nOverall, the results meet the level required for a publication in Nature Communications. However, at the\nsame time, I have several points the authors must necessarily address before recommending the manuscript\nfor publication. Please find below additional points and comments:\nWe are grateful to the referee for deciding that the revised manuscript meets the high standards of Nature\nCommunications and for their recommendation to publish the revised manuscript.\n1) References. In my opinion there are some missing references concerning sensing or quantum sensing of\npressure and temperature. For instance, Ref. (5) in the caption of Table I, although mentioned in the table\nand used for comparison, is not appearing in the reference list. The same seems to occur also for Ref. (6),\n(8) and (9) of the same Table I. These works should be included in the reference list and properly cited (in\nthe introduction and/or in the discussion part) since the authors are basing on their results to show the\npotential of their molecular sensor.\nHere's possible other works the authors could consider to cite:\n- https://www.nature.com/articles/s41467-024-52272-y\n- https://www.tandfonline.com/doi/full/10.1080/26941112.2021.1964926\nWe appreciate the referee’s suggestion of these additional references. We have now updated the manuscript\nto include these works in the main reference list and included the references of Ho et al. and Wang et. al.\nThe formatting issues with Table I references have also been corrected.\nIt seems also that Ref [33] of the manuscript has been recently published and it is no more a preprint:\nhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.120801\nWe have updated the manuscript to include the published version in the reference list.\nThe introduction mentions the potential of molecular spins systems for quantum sensing. In my opinion,\nthe authors are missing some recent developments on both the theoretical as well as the experimental side,\nwhich should be added to the references:\n● https://iopscience.iop.org/article/10.1088/2058-9565/ad985e\n● https://www.nature.com/articles/s41534-024-00838-5\n● https://www.sciencedirect.com/science/article/abs/pii/S0304885319311199?via%3Dihub\n● https://www.nature.com/articles/s41565-024-01724-z\n● https://pubs.acs.org/doi/10.1021/jacs.2c07692\n● https://pubs.aip.org/aip/jcp/article/158/16/161103/2885321/Toward-quantum-sensing-of-Chiral-\ninduced-spin\nWe appreciate the referee’s recommendation of these additional quantum sensing references and believe\ntheir incorporation strengthens the context for and content of this work. We have drawn inspiration from\nthese papers and have updated our introductory references to include them.\n2) Doping level. The authors mention that the doping level of the crystal can be eventually high\n(introduction). However, the concentration used in the experiments is 0.1% corresponding to a collection\nof 10^9 spins and a volume of 2.6 ∙ 10−5 𝑚𝑚3 (Section II). This is giving FWHM linewidth of ≈ 4.8 𝑀𝐻𝑧. This concentration value is not so small and even so large. Could the authors comment on how the linewidth\nis affected by the concentration?\nWe thank the referee for the question. The ODMR lineshape exhibits a distinctive asymmetric profile,\nwhich we addressed in a previous manuscript [1]. The linewidth is primarily governed by hyperfine\ninteractions with proximal 1H nuclear spins in the pentacene aromatic rings [1] . While increased linewidth\nat higher concentrations is expected due to inter-electron interactions [2], the behavior is more nuanced.\nSeveral competing processes—such as singlet fission and triplet-triplet annihilation—contribute to the\ndynamics and are typically described using a Jablonski diagram that captures the relevant transition rates\n(see Ref. [3] for further discussion).\nWe also note a synthetic limitation in the achievable doping concentration for the p-terphenyl host, where\nit is difficult to exceed ~3% pentacene loading. In alternative host materials, however, higher concentrations\nmay be feasible. We plan to explore these possibilities in future work and have expanded the discussion\nand references in the revised manuscript to clarify these\npoints.\nAnd on how much the concentration could be, in principle,\nincreased or further decreased?\nCrystal preparation constrains the theoretical maximum and\nminimum pentacene concentrations we can achieve.\nExperimentally, we have prepared doped crystals with\nconcentrations up to 0.3% by mass (Fig. 1). Although\nhigher concentrations are in principle possible for this\nsystem, a comprehensive study of the effects of such high\nconcentrations has not yet been conducted (to the best of\nour knowledge), excluding the results described in [3] on\nthin films. Pentacene may likely have increased solubility\nin the crystal melt when doped into different host systems,\nFigure 1: PDP crystals synthesized with\nresulting in a higher concentration in the final crystal. We\nvarying pentacene concentrations. From left\nare actively investigating the use of other hosts to produce\nto right: 0.3%, 0.1%, and 0.05% pentacene\ndifferent solid solution crystalline materials.\ndoping, highlighting precise control over\nLower pentacene concentrations are achieved by diluting\ndopant levels and the ability to tune\nthe starting concentration of the pentacene/p-terphenyl\nconcentration across a broad range.\npowder. The lowest concentration we have explored thus far is 0.025% by mass, but we anticipate that\nlower concentrations can be achieved.\n3) Sample size. The sample shown in Fig. 1.c has a remarkably large size for a single crystal. However, the\nfraction of the volume used for experiments is only 2.6 ∙ 10−5 𝑚𝑚3 which means that most of the volume\navailable is effectively not necessary and not used during experiments. The same holds by considering the\nsample volume reported in Supplementary Material (Experimental Setup section). Which are the factors\nlimiting the use of a larger sample volume?\nWe thank the referee for the thoughtful question. Our proof-of-concept experiments were deliberately\nconducted on a relatively small ensemble of spins, guided by two key motivations. First, our primary goal\nwas to characterize the intrinsic sensitivity of the PDP material to environmental variables—specifically,\nthe shifts in ODMR frequency with temperature and pressure, denoted ∂f/∂T and ∂f/∂P. These parameters\nreflect the material’s inherent responsiveness to thermal and mechanical stimuli and are largely independent\nof experimental conditions such as photon collection efficiency or instrumentation. Our measurements\nindicate that these shifts are significantly larger than those observed in NV centers in diamond.\nSecond, we chose to demonstrate these effects using cw laser excitation, aiming for practical deployment.\nSince PDP crystals are inexpensive to synthesize, we sought to show that both the materials and the\nmeasurement infrastructure can remain low-cost.\nUsing larger spin ensembles would indeed improve absolute sensitivity. Prior work in dynamic nuclear\npolarization (DNP) [4,5] and pentacene-based masers [6] has leveraged large para-terphenyl and\nnaphthalene crystals for this purpose. However, these experiments typically require pulsed laser excitation\nto illuminate larger volumes and must consider depth-dependent absorption (Ref. [7] identifies ~589 nm as\noptimal). Adapting such strategies could yield substantial sensitivity gains for bulk pressure and\ntemperature sensing.\nHow does the RF/MW field inhomogeneity affect the FWHM linewidth?\nThe referee raises a valid concern regarding RF inhomogeneity. RF/MW field inhomogeneity will increase\nthe experimental FWHM linewidths. In the setup used in this work, however, the RF field is effectively\nuniform across the probed spin ensemble. This is achieved through the use of a solenoidal coil geometry,\nwhich confines the detection region well within the zone of RF homogeneity. Additionally, the design of\nmicrowave coils or resonators with large homogeneous volumes is well established—even for centimeter-\nscale crystals—as demonstrated in DNP and maser experiments. Instead, the dominant contribution to the\nobserved linewidth is from hyperfine interactions with protons in the host material. This broadening can be\nreduced by deuteration [8].\n4) Cost reported for sample in Fig. 1.c. The cost for the large crystal is estimated in 2.25 US dollars\naccounting only for materials. I really appreciate the comparison in terms of cost of production between a\nsynthetic crystal and an artificial diamond (such as NV centers). However, in my opinion the comparison\ncould be further extended and detailed. Possible points of interest for considering the cost might be:\n- artificial diamonds are grown by chemical vapour deposition of by high-pressure high-\ntemperature methods. Nitrogen and vacancies can be then created by ion implantation or neutron irradiation\nfollowed by thermal annealing. This initial difficulty can be overcome considering that there are specialized\ncompanies offering commercial NV centers.\n- molecular spins offer an easier way of fabrication due to chemical synthesis. Here, however, raw\nmaterials with adequate quality and purity might be necessary and specific chemical techniques and chemical\nfacilities for purification or making reactions. The recipe could require several complex steps and could be\nnot so easy to be obtained or optimized at the beginning. The yield of the reaction could be not so high.\nNormalizing the cost over the mass of the product might be misleading as well. An alternative could be to\nnormalize over the density of the sample or on the spin concentration obtained (spins centers per unit of\nvolume). This extended discussion could be added in a dedicated section of the Supplementary Material.\nWe thank the referee for their commendation of our cost comparison between the PDP crystal and NV-\ndiamond materials. Please see the following breakdown for how we arrived at our conclusions from a\nmaterials and preparation angle. We have also updated the Supplemental Information to include a section\non “Cost Analysis” for interested readers. Note that we have updated the discussion to normalize by spin\ndensity, which is a more relevant metric in this case.\nCost Analysis\nHere, we detail how we arrived at the $2.06 materials cost per crystal quoted in the main\nmanuscript. Note that all prices quoted are current as of 4/22/25.\nMaterials Costs\nFor a typical PDP crystal, ≈ 1 mg of pentacene is doped into ≈ 1 g of p-terphenyl. Referencing Sigma\nAldrich prices of $179 for a 100 gram stock bottle of p-terphenyl and $1350 for a 5 gram stock of pentacene,\nthis comes to $2.06 per ≈ 1g crystal sample ($0.00206 per mg or $0.00000249 per ppb pentacene). NV−\ndiamond samples are typically purchased from specialized commercial entities, eliminating the need for in-\nhouse high cost instrumentation for chemical vapor deposition (CVD), high-pressure high-temperature\n(HPHT) growth, and beamline work. A representative ThorLabs-supplied, Element Six-fabricated\ncommercial DNVB1 single crystal NV− diamond sample has 300 ppb NV− concentration and is sold at\n$1542.24 ($97.92 per mg or $5.14 per ppb NV−). The highest concentration DNVB14 diamond sample\nthey supply has a 4.5 ppm NV− concentration, costing $3325.46 ($211.14 per mg or $0.74 per ppb NV−).\nFixed Costs Associated with Growth\np-terphenyl and\npentacene are purified\nFigure 2: Homebuilt apparatus for high-throughput growth\nin-house prior to the\ncrystal growth, so it is of large PDP crystals. Each modular setup—comprising a\nuseful to consider how custom-built furnace and motor assembly—enables the growth\nthis extra purification\nof multiple centimeter-scale PDP crystals within 24 hours. Five\nstep contributes in the\ncost analysis. P-\nsuch devices, designed for parallel operation, are shown.\nterphenyl is purified via\nzone-refinement. The\nsetup we use employs\nnichrome wire, a 24 V\npower supply, glass\ntubing, a mechanical\nshuttling system\n(actuator and motor),\nand a motion control\nprogrammer. The\nprimary costs here are\nfor the power supply,\nmechanical actuator,\nFigure 2: Homebuilt apparatus for high-throughput growth of large PDP\nand motion\ncrystals. Each modular setup—comprising a custom-built furnace and motor\nprogrammer, which\nassembly—enables the growth of multiple centimeter-scale PDP crystals within\ncost $52, ≈$270, and\n24 hours. Five such devices, designed for parallel operation, are shown.\n$46, respectively.\nPentacene is purified via sublimation, accomplished in a home-built horizontal furnace. This setup consists\nof wire, a 24 V power supply, glass tubes, and high purity Argon gas. Presuming excess wire and glass\ntubes remain from the zone refinement setup construction, the primary cost of this step are the Ar gas\ncylinder and the power supply: $66 and $52, respectively.\nBridgman crystal growth is done in a home built furnace which uses wire, a ceramic tube, a 24 V power\nsupply, a mechanical shuttling system, and a motion control programmer. The primary costs here are the\npower supply, shuttling system, and the motion control, $52, ≈$270, and $46 respectively. The total cost,\ninclusive of preparation and crystal growth supplies, is a fixed ≈$900 addition to the overall material price.\nOnce multiple crystals are produced, the additional cost per crystal is just the material cost ≈$2.\nSummary\nFrom a purely materials standpoint, even without normalization, buying the two stock chemicals to make a\nPDP crystal is cheaper than buying the cheapest ThorLabs-supplied Element Six diamond sample ($1529\nvs. $1542). Normalization by mass ($0.00206 per mg PDP vs. $97.92 per mg or $211.14 per mg NV-\ndiamond, depending on the sample) OR by spin density ($0.00000249 per ppb pentacene vs. $5.14 per ppb\nNV− or $0.74 per ppm NV, depending on the sample) further highlights the cost benefits of using PDP\ncrystals, relative to NV centers. The additional cost for the two purification and growth setups is a one-\ntime, initial ≈$900 investment (≈$350 per step) which is still cheaper to produce at scale than commercial\nchemical vapor deposition instrumentation for diamond fabrication. For example, we have developed an\nin-house scale crystal production setup capable of mass-producing samples (Fig. 2). With all sample\nproduction and material costs taken into consideration, we conclude that PDP crystals are a significantly\ncheaper alternative relative to NV− diamonds.\nIt seems that there is a slight broadening of the signals as the temperature is increased from 100 K to 300\nK. However, Fig. 1.D and 1.E suggest the broadening of the lines occurs at low temperature, not at 300 K.\nCan the authors comment on this point?\nWe apologize for the confusion; the 3D visualization was used to make the shift more visually apparent and\nappealing in Fig. 2. However, we now realize it may have a deceiving effect on the eye for panel A. To aid\nin interpreting this data, we unambiguously show the frequency shift as a function of measured temperature\nin Fig. 2B. There is a consistent line broadening with decreasing temperature. \n6) Section III, the change in the spectral frequency 𝑑𝑓⁄𝑑 𝑇 (and its equivalent for pressure sensing 𝑑𝑓⁄𝑑𝑃).\nIt is stated that this quantity is material-specific and independent by the measurement apparatus or light\ncollection efficiency. The temperature (or the pressure) is changed in the environment (cryostat or pressure\ncell) it is a global macroscopic experimental parameter of the whole sample (not a local one). Moreover,\nthe setup it is said to be not optimized for sensitivity and that the collection efficiency affects the measured\nsignal. In my opinion, the sample size (number of spins), the laser power, the RF/MW power can affect the\nabsolute signal measured. So, one might expect 𝑑𝑓⁄𝑑 𝑇 (or 𝑑𝑓⁄𝑑 𝑃 ) to be affected by the setup and\nexperimental conditions as well. Could the authors better clarify this point?\nThe resonance frequency—if measured with sufficient precision—is governed by the intrinsic interaction\nbetween the spin system and its environment (temperature or pressure). Temperature- or pressure-induced\nchanges in the spin Hamiltonian (e.g., via lattice strain, crystal field effects, or spin–phonon coupling) shift\nthe resonant frequency, not the signal amplitude or quality of measurement. In this sense, the slope 𝑑𝑓⁄𝑑𝑇\n(or 𝑑𝑓⁄𝑑𝑃) is expected to be independent of the measurement apparatus under ideal conditions,\nIn this work, laser and RF/MW power were used within their linear regimes, and global\ntemperature/pressure changes were well-controlled across the sample during measurement to minimize or\neliminate drift-associated changes to the resonance frequency. To better clarify this point, we have revised\nthe Table I caption in the main paper where this was stated to read:\n\"Slopes of ODMR frequency variations 𝑑𝑓⁄𝑑𝑇 and 𝑑𝑓⁄𝑑𝑃 are material properties and reflect\nthe intrinsic spin–environment interactions in the host material, provided that extrinsic\nperturbations (e.g., local heating, power broadening) are avoided. The signal strength and\ndetection sensitivity (𝜂T, 𝜂P) are affected by experimental parameters such as laser power,\nsample size, and RF/MW conditions.\"\n7) End of the Section III. It is mentioned that the sensitivity 𝜂 = 𝜎√𝜏/ 𝑑𝑇 depends on many experimental\nparameters, including number of spins and collection efficiency so, it ultimately depends by the apparatus\nand experimental conditions. I agree with the definition of sensitivity used by the authors in the manuscript\n(which includes also the change in the spectral frequency). In my opinion introducing the noise floor level\nand the integration time with the mentioned definition of sensitivity can give a better comparison among\ndifferent experiments and, eventually, setups and samples. This is because it can be a way to normalize the\nchange in the spectral frequency over different experiments and apparatus. Could the authors comment on\nthis point?\nWe agree that sensitivity—defined as 𝜂 = 𝜎√𝜏 / (𝑑𝑓/𝑑𝑇)—is not solely a material property but is strongly\ninfluenced by the experimental setup, including factors such as collection efficiency, number of spins, and\nnoise characteristics. Indeed, the inclusion of the noise floor σ and integration time τ in the definitions of\ntemperature and pressure sensitivity we provided gives a complete and practical description of sensor\nperformance. This form allows for a direct comparison between different experiments and platforms\nthrough normalizing by measurable, apparatus-dependent parameters.\nWe have updated the manuscript to explicitly state this:\n“This definition incorporates both intrinsic properties (e.g., spectral shift) and extrinsic factors\n(e.g., noise level and integration time), and thus serves as a comprehensive figure of merit for\ncomparing different experimental setups and material systems.”\nWe have also updated the “Sensitivity Measurement” section of the SI to now report the estimated values\nof σ and τ for our measurements, and we emphasize that optimization of these parameters—along with\nimprovements in collection efficiency and spin ensemble size—could significantly improve the overall\nsensitivity.\nIn my opinion the reader would benefit from having more details about the available experimental\nparameters …. This could be part of an extended Table I in Supplementary Material.\nWe note that an apples-to-apples comparison between sensor platforms is challenging, given that the papers\nreferenced for other sensor platforms did not always provide all the experimental details mentioned. With\nthis in mind, we have expanded the platform comparison table in the Supplementary Information of the\npaper to include laser power, collection efficiency, and spin density (ppm) as reported. Parameters not\nexplicitly reported were calculated to give reasonable estimates for purposes of evaluation.\n9) Protocol used for quantum sensing. The manuscript is citing a preprint by almost the same group of\nauthors (Ref. 34) in which quantum sensing of magnetic field is experimentally realized with a similar\npentacene-doped crystal and using again an ODMR approach. The sensing protocol in Ref. 34 seems to be\nfully pulsed-wave in the sense that both optical pulses and RF/MW pulses are used, while in the present\nmanuscript the optical excitation is given in continuous wave. Could the authors explain why they chose to\nuse a continuous wave protocol instead of a fully pulsed-wave one? Is there any advantage in running the\nsensor for pressure or temperature this way? In my opinion, running the sensor in pulsed-wave and\nexploiting its quantum coherence (as type II sensor according to Ref. [1]) would give more convincing\nevidence for a quantum sensing protocol (not only a larger contrast).\nA CW protocol was employed instead of the pulsed protocol used previously (Ref 3), because we designed\nthe experiments with an eye towards low-cost applications. A fully CW protocol facilitates the use of\ncommercial lasers, which can be obtained in cheap, compact form factors. For example, the laser powers\nemployed in these measurements are ~16 mW, a range easily covered by commercially available 532nm\ndiode lasers. Electronics in the 1300-1500 MHz microwave frequency ranges employed are already\ncommercially available, and the material itself costs only ~$2 to make (see response to Referee 1 Question\n4).\nIn total, the cost-effectiveness of individual technological components used here present a readily\nscalable pressure / temperature sensing platform. As noted previously, we emphasize that even with a\nsimple CW scheme, we achieve record pressure sensitivities. The high sensitivity is intrinsic to the material\nused and is independent of the high SNR a pulsed protocol would provide a more commercially relevant\nresult.\n10) Experimental setup. The experimental setup is described in detail. However, there is no information on\nthe optical power reaching the sample or on the RF/MW ones.\nThe reader might benefit in such additional technical information about the protocols and on how the\nexcitations and given and which is their timing or duration (see also the introduction and point 9 above).\nAdding details about the role of the lock-in and on how the contrast is extracted from experimental data\nmight help the audience which is not familiar with ODMR. This information could be added in\nSupplementary Material.\nWe thank the referee for pointing out where the description of our experimental setup could benefit from\nadditional detail. We discuss the relevant experimental parameters here and have added information to the\nSI. For all experiments, we can only report the laser power at the optical window (either of the cryostat or\nthe pressure chamber) because the laser power meter head is too large to fit inside the cryostat or pressure\nchamber itself. The laser power reaching the optical window was 110 mW and the MW power fed through\nthe single loop resonator was ~ 1 W for pressure sensing experiments and ~0.3 W for temperature sensing\nexperiments. We have updated the SI with this experimental information.\nThe PL is collected using convex lenses and converted into an electrical signal using an Avalanche\nPhotodiode (APD) module (Hamamatsu, C12703). The electrical signal is demodulated with a lock-in\namplifier (SRS model SR830 DSP), whose reference signal modulates the RF (ON/OFF) at 1 kHz. ODMR\ncontrast is defined as the change in the PL signal when the RF power is ON and OFF, divided by the PL\nsignal when the RF is OFF. We have updated the SI with this experimental information.\nFor more detail about the ODMR measurements, Figure 1 has been updated with the cw-sensing protocol\nemployed and the SI was updated with a brief description of how contrast is calculated in the “Contrast\nMeasurement” section. The same detection scheme was used for all experiments.\n11) It could be helpful to add a guide for eyes also in Fig. 3.A and 3.B, in a way similar to what was done\nin Fig. 2.A and 2.B.\nWe appreciate the referee’s suggestion and have added a guide to the eye for clarity in Fig. 3A and 3B.\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 2\nIn the submitted manuscript, the authors report on the utility of pentacene-doped in p-terphenyl host lattice\nas pressure and temperature sensor. The main idea behind the study is the leveraging of flexible nature of\nmolecular crystals, relative to the well-investigated diamond lattice hosting NV centres, as a better sensor\nmaterial. The manuscript is well-structured and fundamental concepts are eloquently presented. The authors\nneed to address the following comments to determine the suitability of the script for publication in Nature\nCommunications.\nWe sincerely thank the reviewer for their thoughtful evaluation and positive remarks on the structure,\neloquence, and clarity of our manuscript. We appreciate the acknowledgment of our study's central idea—\nutilizing the flexible nature of molecular crystals, specifically pentacene-doped p-terphenyl, as a promising\nalternative to rigid diamond lattices for pressure and temperature sensing. We have carefully considered all\nthe reviewer’s comments and addressed them point by point in the revised manuscript and the\naccompanying response document.\nTitle: The term organic crystals is rather general. I think the title would be more informative, if the authors\nuse “pentacene-doped p-terphenyl single crystals” instead of organic crystals.\nWe agree that specifying the material used can make the title more informative and precise. Accordingly,\nwe have revised the title to: “High sensitivity pressure and temperature quantum sensing in pentacene-\ndoped p-terphenyl single crystals”\nAbstract: Please mention temperature and pressure ranges studied.\nWe have revised the abstract to include the specific temperature and pressure ranges studied in our\nexperiments for improved clarity and context for the reader.\nI. Introduction\n1. The authors cite references 28 and 29 as dealing with rare-earth ions. While it’s true 29 deals with rare-\nearth ion (Eu3+), the reference 28 deals with Cr4+ molecules, a transition metal system. Please correct this\ndiscrepancy by rewriting the sentence. There is a typo: “utilizing are-earth ions”\nWe apologize for the typo and have corrected this line in the introduction to “utilizing rare-earth or\ntransition-metal ions”.\n2. What does the authors mean by tunable sensor placement in three-dimensions? Please elaborate.\nWe apologize if our phrasing caused any confusion, and we clarify here. In the phrase “tunable sensor\nplacement in three-dimensions”, we are referring to molecular quantum sensors used as linkers in metal-\norganic frameworks (MOFs) [9]. These crystalline porous materials are highly modular in their\nconstruction, so changing the identity of the linker or the metal ion / metal cluster node can adjust the\nsensor’s spatial configuration through altering the MOF structure [10]. For added clarity in the introduction,\nwe have changed the wording in the following text:\n“These systems offer advantages stemming from bottom-up synthesis, tunable sensor placement in\nthree-dimensions via integration into porous materials and molecular-level control over sensor\nproperties”.\n3. For easy referencing, the authors can give values for the size of the single crystals and doping levels of\nsensor molecule in a host.\nWe have included the single crystal size and doping levels in the following phrase in the introduction:\n“Additionally, the material can be grown into large single crystals (3 cm) with high doping levels (~1000\nppm)”.\nII. System and principle\nDoes the doping concentration affect the sensing capability of the system?\nAdditional mechanisms set in at higher doping concentrations which make it challenging to unambiguously\npredict sensing capabilities at higher doping levels. We discuss contributing factors below.\nThe doping level of 0.1% (w/w) (~827 ppm) pentacene achieved here is high, compared to the record\nin similar quantum sensing materials. For example, semiconductor defects like the NV- center have\nachieved up to ~16 ppm [11]. As discussed in our response to Referee 1 Question 2, we have grown crystals\nwith dopings up to 0.3% (w/w) thus far (see Fig. 1 of that same response), with the upper % doping limit\nset by pentacene’s solubility in the p-terphenyl melt. Pentacene may have a higher solubility in other host\nmaterials.\nIn our current samples, ODMR linewidths are principally broadened by hyperfine coupling to proximal\nnuclear spins. Since the pentacene is dilutely incorporated into the lattice (~1:1209 pentacene:p-terphenyl\nmolecules), we expect that electron-electron dipolar interactions contribute minimally to peak broadening,\nwhich would decrease sensing capability.\nAt high pentacene concentrations in PDP thin films, previous work demonstrated the onset of other\ntriplet pathways, such as singlet fission and quintet state formation [3]. Furthermore, as the inter-pentacene\ndistance decreases, we may expect a greater relaxation contribution from dipolar interactions.\nIn summary, the high concentration molecular quantum sensor regime is an exciting but not yet well\nexplored parameter space. We expect that striking the balance between high sensor concentration and\nminimal feeding of other triplet pathways to be the optimal triplet molecular quantum sensor profile.\nThe figure 1E is labelled with 79 K, while the text says 77 K.\nWe thank the referee for pointing out this typo. The correct temperature is 79 K, and the manuscript has\nbeen updated accordingly.\nPlease show the TXZ linewidth at 79 K (77 K?)\nFigure 1 has been updated to show the TXZ linewidth, 8.9 MHz.\nIII. Triplet ODMR variation with temperature\nIn Figure 2C, the authors can add temperatures for easy referencing of temperature-dependent phase\nchange.\nFigure 2C has been updated with the measured temperature corresponding to each para-terphenyl crystal\nstructure.\nSince pentacene performs a useful function, the authors can write “sensitive reporters” instead of “sensitive\nspectators”\nWe have incorporated the suggested change in the manuscript.\nIn figure 1D and E, the ODMR frequencies of XY and XZ transitions increase with decreasing temperature.\nHowever, in figure 2A, for XY, the trend seems opposite. I am a bit confused how to interpret the data\npresented in the figures.\nThere was a mistake made in Illustrator during the figure preparation, we sincerely apologize for this error.\nThe correct trend is that the transition frequency decreases with decreasing temperature for the YZ and XZ\ntransitions and increases with decreasing temperature for the XY transition, as shown in Figure 2B. We\nthank the referee for noticing this error. We have corrected the figure in the revised manuscript.\nThe attribution of drop occurring after 290 K to the crystals being close to the melting point (486 K, as\nmentioned by the authors) is rather tentative. The issue is compounded by almost 200 K difference. Could\nthe authors provide a more logical explanation?\nWe thank the referee for their comment. In general, the polarization lifetime decreases with increasing\ntemperature due to the Boltzmann distribution. Also, triplet population and depopulation rates will change\nwith increasing temperature, likely shortening the triplet state lifetime. This may also be related to signal\nloss from exciton delocalization at elevated temperatures; exciton hopping barriers are typically in the range\nof 25 meV. These are more logical explanations for why contrast decreases in this regime of the plot, rather\nthan approaching the melting point, which is much farther away in temperature. We have updated the\nmanuscript accordingly to read the following:\n“Another drop occurs after the\nplateau past 290 K, likely due to\nexciton delocalization at elevated\ntemperatures and increasing\ntemperature decreasing the\npolarization lifetime and changing\nthe intersystem crossing rates and\ntriplet depopulation rates.”\nApart from the frequency shift with\nrespect to temperature, the intensity\nof the ODMR transitions seems to\nchange with temperature. Could this\nintensity variation used to sense\nFigure 3: Variation of photoluminescence intensity with\ntemperature, more like\ntemperature.\nluminescence thermometry\n(https://doi.org/10.1002/adma.202302749) reported for luminescent molecular and solid-state systems?\nIt would be interesting, if the authors make a comparative study between intensity and frequency variation\nwith respect to temperature.\nWe thank the reviewer for their suggestions for developing this system as a multimodal sensor platform.\nAs the intersystem crossing (ISC) rate decreases with decreasing temperature [12], a higher PL is observed\nat lower temperatures (see Fig. 3). This is because most of the pentacene molecules undergo spontaneous\nemission from the excited singlet state to the ground singlet state, rather than undergoing ISC into the triplet\nstate.\nIn Fig. 3, we have plotted the PL vs. temperature graph below and estimated the relative thermal\nsensitivity, Sr(T)=0.11%, using the expression:\nSr(T) = (1 / PL(T)) × (dPL(T) / dT) × 100% = 0.11%.\nThe deviations from linearity are not currently completely understood. We are continuing to explore these\ndeviations and the potential causes, including that the response may simply be nonlinear. While there is not\na large PL variation with temperature, it is an interesting angle that we will explore in the future.\nIV. Triplet ODMR variation with pressure\nWhy the authors chose to study Tyz and Txz transitions? What is the rationale behind leaving out the Txy\ntransition?\nInterestingly, not all pentacene triplet transitions demonstrate the same pressure sensitivity. In particular,\nthe T_XY transition is not as sensitive to pressure over the applied ranges studied as the other two\ntransitions, T_YZ and T_XZ. We have included the plots of the T_XY transition frequency’s variation with\npressure below (see Fig. 4) and in the SI, as we did not have space to include it in the main paper.\nAdditionally, we have updated the following line in the manuscript to make this point clearer:\n“Fig. 3A-B presents\nrepresentative ODMR\ntraces for the TYZ and\nTXZ transitions only,\nsince the T_XY transition\nis not as sensitive to\npressure over the applied\nranges studied (see SI\nFigure 4: Frequency variation of the Txy transition with applied\nFig. 4).”\npressure.\nVI. Conclusions\nI do agree with the authors that the studied system is interesting. However, I have difficulties accepting the\nsystem as a compelling pressure and temperature sensor.\nIn our humble opinion, the pentacene-doped para-terphenyl (PDP) system shows strong potential as a\npressure and temperature sensor. Its high sensitivity coupled with low experimental costs and scalable\nproduction make it well-suited for practical applications, as detailed below.\nAs discussed in responses to Referee 1 Questions 4 and 9, the material costs to set up scale crystal\nproduction are modest. Each crystal costs approximately $2 with a one-time infrastructure cost of $900.\nThe equipment needed to run experiments, a cw 532 nm laser and microwave electronics, are commercially\navailable. Aside from the initial investment in crystal production and acquiring equipment, the barrier to\nadopting this technology is low.\nWe envision this system evolving into a deployable quantum sensor, akin to existing NV-diamond\nmagnetometers [13]. Its low component cost and compact footprint support the development of a portable\nsensing platform. Both single crystal and thin film PDP form factors can be evaluated to determine which\nis better suited for such applications.\nThe PDP system’s 1–2 bar optimal pressure range aligns with key use cases, including tire pressure\nmonitoring, hydraulic fluid sensing, and altimetry—each requiring reliable detection of small pressure\nchanges (see Page 13 for a more detailed discussion). The high sensitivity demonstrated by this organic\ncrystal also points to a broader class of organic molecule-based pressure sensors. Since pressure sensitivity\nis largely governed by the Young’s modulus of the host lattice—which can be higher in organic molecular\nsystems than in semiconductor defect systems—we anticipate further development of such sensors. Organic\nmolecules spatially arranged via incorporation into MOFs offer a promising direction for expanding this\nmaterial class.\nThe same applies to the “elimination of reliance on electronic defects…” In my humble opinion, the\nstatements are far-fetched and require rewriting.\nThe referee’s point about the elimination of semiconductor defect materials is well taken, and we have\nrephrased the discussion and outlook phrase to highlight molecular quantum sensors as a complementary\nmaterial platform to defects in semiconductors with the following language:\n“This approach does not rely on electronic defects in semiconductor lattices and opens new design\npossibilities through chemical synthesis.”\nCould the authors discuss how the chemical design strategies can be leveraged to improve the sensitivity\nof the crystalline system discussed in the manuscript? For example, could deuteration enhance the optical\nproperties with the consequent effect on sensing capability?\nTwo chemical design strategies that can improve the sensitivity of the crystalline system employed are\ndeuteration of the host pentacene molecule and utilization of a pentacene derivative, 6,13-diazapentacene.\nAs demonstrated in the X-band EPR study by Sloop et. al. [14], deuteration of the pentacene host increases\nthe triplet state lifetimes of the T and T states (the T state is relatively unchanged) and slightly improves\n+1 -1 0\nthe polarization lifetime for the T to T transition and T to T transition (T to T is slightly worsened).\n0 +1 -1 +1 0 -1\nWhile the population rates of the 1 and -1 sublevels are slightly decreased relative to fully protonated\npentacene, the difference in the population rates is improved, which would increase polarization in this\ntransition (Table 1). We anticipate that the cumulative effect of improvement in triplet state lifetimes,\npolarization lifetimes, and triplet population rates would improve the polarization and enhance the SNR of\nthe measurements.\nPopulation rate Spin-lattice decay Decay rate\nrate(a)\nPentacene-d₁₆ P₁ = 0.4 ± 0.05 W₁ = 1.77 × 10⁴ k₁ = 7.52 × 10³\nP = 016 ± 0.02 W₂ = 2.86 × 10⁴ k₀ = 10³\nPentacene-h₁₄ P₁ = 0.44 ± 0.05 W₁ = 1.85 × 10⁴ k₁ = 1.52 × 10⁴\nP₀ = 0.09 ± 0.02 W₂ = 2.63 × 10⁴ k₀ = 10³\nP₋₁ = 0.47 ± 0.05 W₃= 0.658 × 10⁴ k₋₁ = 1.39 × 10⁴\nTable 1: Triplet state parameter comparison between deuterated and protonated pentacene doped in para-\nterphenyl. Reproduced from Ref 14.\n\\⁽ᵃ⁾ W₁ is the rate for |0⟩ ↔ |+1⟩ transition, W₂ for |0⟩ ↔ |-1⟩, and W₃ for |-1⟩ ↔ |+1⟩.\nThe best fit of the kinetic parameters at 25°C (s⁻¹). The estimated errors for all the parameters except k₀ are\n±10%. The estimated error for k₀ is ±50%.\nSimilarly, 6,13-diazapentacene-doped para-terphenyl has recently been shown as a high contrast quantum\nsensing material (Fig. 5) for magnetometry applications [15]. Since the primary temperature and pressure\nsensitivity properties we show here result from the p-terphenyl lattice phase transitions and compressibility,\nwe anticipate pressure and temperature sensing would be possible with this doped crystal as well, again\nwith higher contrast and improved measurement SNR.\nLastly, pentacene or its chemical-derivatives could be incorporated as a building block into porous\ncrystalline materials [16],\nsuch as metal-organic\nframeworks, for tunable\nsensor placement in 3D\nporous materials [17].\nA minor remark:\nThere is\nalways a space between value\nand unit: for example, please\ncorrect 77-330K in the\nintroduction, in the caption of\nFigure 1, and other parts of the\nmanuscript.\nWe thank the reviewer for this\nFigure 5: Chemically tuning the ODMR contrast (from Ref. 14)\nremark. We have carefully\nrevised the manuscript and\nensured that a space is\nincluded between numerical values and units throughout the text, including in the Introduction, Fig. 1\ncaption, and all other relevant sections.\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 3\nSingh et al. described a quantum sensing system based on pentacene in p-terphenyl crystals, which\ndemonstrates high sensitivity to temperature and pressure through shifts observed in optically detected\nmagnetic resonance (ODMR) spectra. While the study presents the novelty of using ODMR to measure\nthese parameters, it is important to note that several key aspects of the work are already well documented\nin the literature. These include the use of pentacene triplet spin states for quantum sensing, the application\nof ODMR (and EDMR) to address these spin states, and the sensitivity of pentacene triplet states to both\ntemperature, including phase changes, and pressure (e.g., ref 42, https://doi.org/10.1021/jp070251v). Given\nthat pentacene triplets are a well-established molecular platform, it is not surprising that the authors were\nable to optically detect spectral shifts and utilize them to sense these parameters. Nevertheless, I recognize\nthat the use of emission-based detection in this context is a novel contribution, and I could potentially\nsupport the acceptance of the manuscript.\nWe thank the reviewer for their thoughtful comments and for recognizing the novelty of our room\ntemperature, emission-based detection approach for quantum sensing using pentacene in p-terphenyl\ncrystals.\nThe pressure ranges accessible with the pentacene-doped para-terphenyl material enable operation in a\ncomplementary pressure range to NV- diamond-based sensors, a benchmark quantum pressure sensing\nmaterial. The organic p-terphenyl crystal lattice is softer than that of the more rigid diamond-based systems.\nMechanical softness enables the lattice to respond more sensitively to lower pressure variations, facilitating\noperation in the low-pressure regime where diamond NV-center sensors are less effective or overly stiff.\nThis expands the application range of quantum sensing technologies.\nWe have added the reference mentioned to our discussion of phase transitions in this material.\nHowever, I would like the authors to address how they envision using this system as a sensor in real-world\napplications. Specifically:\n● What types of target environments would this sensor be used for?\n● Why are such capabilities necessary or advantageous in those contexts?\nWe thank the referee for raising this point. We envision a broad range of applications for PDP crystals\nacross diverse domains. While our discussion here is focused more on pressure/strain sensing, similarly\nwide applications can be envisioned for temperature sensing.\nStrain-mediated spin actuation: One particularly compelling application lies in the strain-mediated\ncontrol of spin systems. Prior studies have shown that electronic spins, such as those in nitrogen-vacancy\n(NV) centers in diamond, can be coherently actuated using strain fields, including standing-wave strain\npatterns produced by H-bar resonators [18] or through diamond cantilever devices [19,20]. This spin-strain\nactuation has evolved into a major research area, including efforts to control spins using single\nphonons [21]. However, the\nimplementation of these ideas in diamond\nhas been hampered by the material’s\ninherently low strain sensitivity. Typically,\nstress levels on the order of MPa are\nrequired to achieve meaningful spin\nactuation [18], necessitating either high-\nstrain cantilevers or advanced\nnanofabrication techniques directly in\nFigure 6: Preliminary work showing pentacene doped\ndiamond—both of which present\ncrystals grown as needle like structures.\nchallenges.\nIn contrast, PDP crystals offer an attractive alternative. These crystals are significantly easier to fabricate.\nIn new unpublished work, we have shown that pentacene-based crystals can be grown in needle-like\nmorphologies, which are directly amenable to use as cantilevers (see Fig. 6). The inherent strain sensitivity\nroughly three orders of magnitude higher than that of diamond makes it possible to actuate spins at\nsubstantially lower strain and power thresholds.\nOptical pressure and strain sensing devices: More broadly, we envision PDP crystals as general-purpose\npressure and strain sensors potentially surpassing the capabilities of classical devices (e.g. strain gauges).\nThese sensors may find applications in contexts such as pitot tubes and altimeters. Furthermore, PDP-based\nsensors may enable measurements in contexts where traditional strain gauges are ineffective—for example,\nin mapping high-resolution strain distributions within heterogeneous materials or small-scale structures.\nFrom an engineering perspective, these crystals are highly compatible with low-cost diode laser systems\nand fiber-based optics. This compatibility paves the way for compact, integrated, and scalable pressure\nsensing platforms, akin to recent fiber-based magnetometers demonstrated in Ref. [13].\nFunctional materials via additive manufacturing: We foresee exciting directions in the development of\nfunctional materials by incorporating pentacene or its derivatives into polymers or 3D-printed structures.\nThese composite materials would have built-in optical readout capabilities for strain, pressure, or\ntemperature, accessible simply through laser illumination. We have previously demonstrated a similar\napproach with NV centers in diamond [16,22]: by embedding NV-nanodiamonds into 3D printing filament,\nwe fabricated intricate structures via two-photon polymerization (TPP) with spatially distributed sensing\ncapability.\nFig. 7 illustrates one such porous gyroid structure, where nanodiamonds (seen as red fluorescence) line the\ninterior pore walls. (Here, green autofluorescence arises from the host resin.) We envision analogous\nstructures incorporating PDP nanocrystals, which would offer the added benefits of simpler processing,\nenhanced sensitivity, and the potential for full-field, in-situ strain mapping. Such capabilities could greatly\nbenefit the design of topologically inspired metamaterials and strain-resilient architectures—areas where\ncurrent in-situ strain measurement techniques remain limited. We also highlight relevant work by Carlos\nPortela’s group at MIT [23], where optical\nspectroscopy was used to map strain fields\nin complex 3D-printed structures. In\ncomparison, PDP-based approaches offer\na potentially simpler, built-in readout\nmechanism with higher sensitivity.\nThin-film strain sensors and acoustic\napplications: Pentacene-based thin films,\npatterned directly onto surfaces, represent\nanother promising platform for strain\nsensing. Optical interrogation of these\nFigure 7: Nanodiamond (ND) quantum sensors in 3D\nfilms could allow for spatially resolved\nstructures assembled via TPP. (A) SEM of diamond\nstrain mapping across a substrate.\nporous structures in a “gyroid” cross section. (B) Zoomed\nApplications may include acoustic or\nconfocal image showing ND in the internal walls. Red\nvibrational sensing [24], where such films\nfluorescence is from NDs while green is autofluorescence\nserve as highly responsive coatings that\nfrom the resin.\ntransduce surface deformations—such as\nthose from sound waves—into measurable optical signals.\nBottom-up engineered nanomaterials: On the nanoscale, we envision using pentacene molecules as\nprototypes of modular building blocks in the construction of mechanically responsive materials—\nparticularly in metal-organic frameworks (MOFs) [25]. The high strain sensitivity of PDPs as we\ndemonstrated in this work, stems from their soft mechanical properties, including a low Young’s modulus.\nIn MOF-like systems, one could chemically tune both the mechanical response by varying the internal pore\nstructure, linker rigidity, and other design parameters. This opens a powerful avenue for bottom-up design\nof smart materials with customizable strain sensitivity, expanding the toolbox beyond what is possible with\nconventional semiconductors or defect centers.\nBiological sensing applications: Finally, we see significant opportunities for PDP nanocrystals in\nbiological contexts. These crystals can be synthesized in nanocrystalline form and functionalized for\nincorporation into living systems. Recent work by Ishiwata and coworkers [26] demonstrated successful\nintegration of such nanocrystals into cells, with low ODMR heterogeneity—thanks to less onerous\nrequirements for mechanical ball milling.\nOnce incorporated, these crystals could serve as intracellular strain reporters. For example, forces applied\nto cells—via optical tweezers or during migration—could be monitored through the embedded PDP\nnanocrystals, enabling studies of cell mechanics, viscoelasticity, and intracellular rheology [27,28]. We are\nalso exploring similar applications in plant systems. In unpublished work from our group (Fig. 8), diamond\nnanoparticles embedded in plant roots yielded ODMR readouts from different regions of the rhizosphere.\nWe believe similar experiments with PDP nanocrystals are not only feasible but potentially advantageous,\nenabling detection of mechanical stress in root tissues in response to environmental stimuli such as drought\nor changes in soil composition. These measurements could shed new light on how mechanical cues\ninfluence plant development.\nIn summary, PDP crystals,\nwith their superior strain\nsensitivity, offer a\ncompelling platform for a\ndiverse range of pressure\nand strain sensing\napplications.\nThe performance criteria\nlisted in Table 1 have\nlimited significance if they\ncannot be realized under\npractical conditions… For\nFigure 8: Nanodiamond incorporated into different parts of a root of example, the authors\na living plant and corresponding ODMR signals (unpublished). highlight the phase\ntransition region values for\ndf/dT at 193 K to demonstrate a significantly larger sensitivity than NV centers. However, what is the\npractical relevance of this temperature in real-world sensing applications?\nWe refer to the more detailed response above. Regarding the practical relevance of sensitivity benchmarks\nlike df/dT at 193 K, we highlighted this value to illustrate the intrinsic potential of the molecular system.\nWhile 193 K may not directly correspond to application-relevant temperatures, it reflects the upper limit of\nachievable sensitivity and highlights physical mechanisms that can be tuned to improve performance at\nroom temperature and beyond—a direction we are actively pursuing.\nDFT calculations also suggest that picometer-scale changes are detectable by the molecular orbitals, even\noutside the phase transition region. In other words, any event producing orbital-level changes at that scale\nwould be detectable, regardless of proximity to a phase transition. We have edited the discussion section as\nfollows:\n“This also suggests new quantum sensor form factors, including thin-films, 3D printed materials,\nand nanoparticles, possibly down to the single-molecule level. The all-optical nature of our\ndetection scheme offers a non-invasive route for local sensing, eliminating the need for physical\ncontact or electrical interfaces for readout and anticipating single cell-deployable molecular\ntemperature and strain sensing tags.”\nA similar concern applies to pressure measurements—what is the significance of detecting variations in the\n1–2 bar range? Without clear justification for these conditions, the claimed advantages of the pentacene\nsystem may not translate into meaningful practical benefits, and the presented results do not carry\nsignificant weight or novelty.\nWe refer to the more detailed answer provided above on potential applications. Pressure variations in the\nnarrow 1–2 bar range are highly relevant in biological and microfluidic contexts, such as monitoring\nchanges in osmotic pressure or intracellular vesicle dynamics [27]. When deployed as nanoparticles, PDP\nmolecular crystal-based quantum sensors can be used for additively manufactured, bottom-up engineered\nquantum sensing materials [16] or functional metamaterials [23]. If PDP nanoparticles are surface\nfunctionalized for biological-compatibility [26], then they can be used for in-cell sensing of small, but\nbiologically meaningful, variations in pressure and temperature.\nOverall, the methodology and data presented appear reasonably sound. I would recommend addressing\nthese points to strengthen the paper's relevance and provide a clearer vision for its potential applications.\nWe thank the reviewer for their favorable comments on our methodology and the quality of our data and\nfor their useful feedback. We hope that the revised version of the manuscript now clearly outlines the scope\nof applications for this system and the significance and novelty of the results.\nMinor comments:\np2: “The PDP crystal in Fig. 1C requires only $2.25 in materials cost, representing a ∼70,000-fold reduction\nin mass-normalized cost compared to NV-diamond.” This requires either citation or some support for the\nnumbers\nReferee 1 had a similar comment related to how we arrived at the stated crystal materials cost, so we refer\nthe reviewer to our answer to Referee 1’s Question #4 and the associated new section of the SI.\np2: “Fig. 1D the case for RT and Earth’s field.” Missing is?\nWe thank the referee for catching this typo and have updated the manuscript accordingly.\nREFERENCES\n[1] H. Singh, N. D’Souza, K. Zhong, E. Druga, J. Oshiro, B. Blankenship, R. Montis, J. A. Reimer, J. D.\nBreeze, and A. Ajoy, Room-temperature quantum sensing with photoexcited triplet electrons in\norganic crystals, Physical Review Research 7, 013192 (2025).\n[2] C. Kittel and E. Abrahams, Dipolar Broadening of Magnetic Resonance Lines in Magnetically\nDiluted Crystals, Phys. Rev. 90, 2 (1953).\n[3] D. Lubert-Perquel, E. Salvadori, M. Dyson, P. N. Stavrinou, R. Montis, H. Nagashima, Y. Kobori, S.\nHeutz, and C. W. Kay, Identifying triplet pathways in dilute pentacene films, Nature\nCommunications 9, 4222 (2018).\n[4] T. R. Eichhorn, B. van den Brandt, P. Hautle, A. Henstra, and W. T. Wenckebach, Dynamic nuclear\npolarisation via the integrated solid effect II: experiments on naphthalene-h 8 doped with pentacene-d\n14, Molecular Physics 112, 1773 (2014).\n[5] P. Hautle and W. T. Wenckebach, Creating high, portable proton polarization with photo-excited\ntriplet dnp, Journal of Magnetic Resonance Open 20, 100159 (2024).\n[6] M. Oxborrow, J. D. Breeze, and N. M. Alford, Room-temperature solid-state maser, Nature 488, 353\n(2012).\n[7] Y. Quan, N. Niketic, J. M. Steiner, T. R. Eichhorn, W. Tom Wenckebach, and P. Hautle, General\ntheory of light propagation and triplet generation for studies of spin dynamics and triplet dynamic\nnuclear polarisation, Molecular Physics 121, e2169025 (2023).\n[8] A. Brouwer, J. Köhler, E. J. Groenen, and J. Schmidt, 13C isotope effects for pentacene in p-\nterphenyl: High-resolution spectroscopy and single-spin detection, The Journal of Chemical Physics\n105, 2212 (1996).\n[9] J. M. Zadrozny, A. T. Gallagher, T. D. Harris, and D. E. Freedman, A porous array of clock qubits,\nJournal of the American Chemical Society 139, 20 (2017).\n[10] Zadrozny, Joseph M., Audrey T. Gallagher, T. David Harris, and Danna E. Freedman. \"A porous\narray of clock qubits.\" Journal of the American Chemical Society 139, no. 20 (2017): 7089-7094.\n[11] V. M. Acosta et al., Diamonds with a high density of nitrogen-vacancy centers for magnetometry\napplications, Phys. Rev. B 80, 11 (2009).\n[12] R. Brown, J. Wrachtrup, M. Orrit, J. Bernard, and C. Von Borczyskowski, Kinetics of optically\ndetected magnetic resonance of single molecules, The Journal of Chemical Physics 100, 7182 (1994).\n[13] R. Patel et al., Subnanotesla magnetometry with a fiber-coupled diamond sensor, Physical Review\nApplied 14, 044058 (2020).\n[14] D. J. Sloop, H.-L. Yu, T.-S. Lin, and S. Weissman, Electron spin echoes of a photoexcited triplet:\nPentacene in p-terphenyl crystals, The Journal of Chemical Physics 75, 3746 (1981).\n[15] S. K. Mann, A. Cowley-Semple, E. Bryan, Z. Huang, S. Heutz, M. Attwood, and S. L. Bayliss,\nChemically Tuning Room Temperature Pulsed Optically Detected Magnetic Resonance, Journal of\nthe American Chemical Society (2025).\n[16] B. W. Blankenship, Z. Jones, N. Zhao, H. Singh, A. Sarkar, R. Li, E. Suh, A. Chen, C. P.\nGrigoropoulos, and A. Ajoy, Complex Three-Dimensional Microscale Structures for Quantum\nSensing Applications, Nano Letters 23, 9272 (2023).\n[17] L. Sun et al., Room-temperature quantitative quantum sensing of lithium ions with a radical-\nembedded metal–organic framework, Journal of the American Chemical Society 144, 19008 (2022).\n[18] E. MacQuarrie, T. Gosavi, N. Jungwirth, S. Bhave, and G. Fuchs, Mechanical spin control of\nnitrogen-vacancy centers in diamond, Physical Review Letters 111, 227602 (2013).\n[19] P. Ovartchaiyapong, K. W. Lee, B. A. Myers, and A. C. B. Jayich, Dynamic strain-mediated coupling\nof a single diamond spin to a mechanical resonator, Nature Communications 5, 4429 (2014).\n[20] J. Teissier, A. Barfuss, P. Appel, E. Neu, Maletinsky, and P, Strain coupling of a nitrogen-vacancy\ncenter spin to a diamond mechanical oscillator, Physical Review Letters 113, 020503 (2014).\n[21] H. Wang and I. Lekavicius, Coupling spins to nanomechanical resonators: Toward quantum spin-\nmechanics, Applied Physics Letters 117, (2020).\n[22] B. W. Blankenship, Y. Rho, Z. Jones, T. Meier, R. Li, E. Druga, H. Singh, X. Xia, A. Ajoy, and C. P.\nGrigoropoulos, Optically Detected Magnetic Resonance Imaging and Sensing Within Functionalized\nAdditively Manufactured Microporous Structures, arXiv Preprint arXiv:2502.16434 (2025).\n[23] Y. Kai, S. Dhulipala, R. Sun, J. Lem, W. DeLima, T. Pezeril, and C. M. Portela, Dynamic diagnosis\nof metamaterials through laser-induced vibrational signatures, Nature 623, 514 (2023).\n[24] Y. Wang, R. Zhou, Z. Liu, and B. Yan, A low-power CMOS wireless acoustic sensing platform for\nremote surveillance applications, Sensors 20, 178 (2019).\n[25] K. Orihashi, A. Yamauchi, M. Inoue, B. Parmar, S. Fujiwara, N. Kimizuka, M. Asada, T. Nakamura,\nand N. Yanai, Radical qubits photo-generated in acene-based metal–organic frameworks, Dalton\nTransactions 53, 872 (2024).\n[26] H. Ishiwata, J. Song, Y. Shigeno, K. Nishimura, and N. Yanai, Molecular Quantum Nanosensors\nFunctioning in Living Cells, (2025).\n[27] A. Vian, M. Pochitaloff, S.-T. Yen, S. Kim, J. Pollock, Y. Liu, E. M. Sletten, and O. Campàs, In situ\nquantification of osmotic pressure within living embryonic tissues, Nature Communications 14, 7023\n(2023).\n[28] H. Knowles, Simultaneous Nanoscale Rheology and Thermometry in Complex Systems Using\nDiamond Nanocrystals, in Quantum Nanophotonic Materials, Devices, and Systems 2023 (SPIE,\n2023), p. PC126570A."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Please, see attached file.", "reviewer_2": "The authors have satisfactorily responded to the criticism of the reviewers and revised the script according to the comments. Therefore, publication of the script in Nature Communications is recommended.\nSigned by\nSenthil Kumar Kuppusamy", "reviewer_3": "The authors have conducted a careful revision, satisfactorily addressing my previous concerns.\nThe manuscript now meets the scientific rigor and presentation standards required for publication in Nature Communications."}, "author_response": "MANUSCRIPT NCOMMS-24-69634:\n“High sensitivity pressure and temperature quantum sensing in organic crystals”\nReferee Comments are in Black; Authors’ Response are in Blue\n——————————————————————————————————————————\nRESPONSE TO REFEREE REPORT 1\nI have carefully checked the revised version of the manuscript by H. Singh and coauthors as\nwell as\ntheir reply to my points. In my opinion, the authors have addressed all my previous points and to\nhave also followed some of my suggestions.\nTherefore, according to my previous report and assessment, I can recommend the paper for\npublication in Nature Communications in its actual revised version.\nHowever, as a final remark and advice for the future, I strongly suggest the author to fully report\nthe\nwhole comments of a Reviewer when addressing them in their reply, without cutting or omitting\nparts of them. More specifically, the original numeration of part of my comments appeared to be\nwrong and it was a little hard to compare them with the authors’ replies. This additional effort\nfrom\nmy side could have been easily avoided.\nThere are several reasons behind this advice:\ni) The peer review file will be made available in case of publication. It would be much and\nmuch better for the readers to be able to track the whole revision history (i.e., full\ncomments and replies). No matters about the length.\nii) This improves the readability of the revisions made by the authors\niii) apparently, a similar thing was not done with the comments of the other Reviewers. This\ncould be misunderstood for a lack of consideration towards one of the Reviewers\niv) The authors should know that omitting part of the considerations and motivations given\nby a Reviewer in his/her report might somehow hide or mask his/her critical thinking on\nthe manuscript.\nAuthor's response: We sincerely thank the reviewer for the positive evaluation of our revised\nmanuscript and for the recommendation for publication. We also appreciate the valuable advice\nregarding the inclusion of full reviewer comments in our future responses.\n—————————————————————————————\n—————————————\nRESPONSE TO REFEREE REPORT 2\nThe authors have satisfactorily responded to the criticism of the reviewers and revised the script\naccording to the comments. Therefore, publication of the script in Nature Communications is\nrecommended.\nSigned by Senthil Kumar Kuppusamy\nAuthor's response: We sincerely thank the reviewer for the positive evaluation and the\nrecommendation for publication in Nature Communications. We truly appreciate the time and\neffort devoted to reviewing our manuscript and are grateful for the constructive feedback, which\nhelped us improve the quality and clarity of the work.\n——————————————————————————————————————————\nReviewer #3 (Remarks to the Author):\nThe authors have conducted a careful revision, satisfactorily addressing my previous concerns.\nThe manuscript now meets the scientific rigor and presentation standards required for\npublication in Nature Communications.\nAuthor's response: We sincerely thank the reviewer for the positive assessment of our revised\nmanuscript and for recognizing the improvements made. We are grateful for the constructive\nfeedback that helped us enhance both the scientific rigor and clarity of the presentation."}]

Decision letter