Proton transfer regulated photocured robust room-temperature phosphorescence from naphthalimide

Domain: physics
Published: 2026-03-21
Editorial outcome: major_revision

Abstract
Photocured room-temperature phosphorescence (RTP) materials have considerable
potential applications but are rarely reported. Here, we reported photocured RTP materials from
naphthalimide, which simultaneously acts as RTP chromophore and photo-initiator. Specifically,
naphthalimide generates radicals to polymerize acrylic acid and acrylamide upon UV irradiation.
The resulting naphthalimide is tightly restricted in in-situ formed crosslinked matrix to achieve
robust RTP (τ =389.58 ms, φ =17.83%, water and organic solvents resistance). Significantly,
p p
carboxyl can bind onto lone-pair electrons of tertiary amine in naphthalimide through proton
transfer hydrogen-bonds (PTHBs), inhibiting nonradiative decay of S induced by photoinduced
1
electron transfer (PET); increasing spin-orbit coupling (SOC) to promote intersystem crossing
(ISC); cooperating with intermolecular hydrogen-bonds afford rigid microenvironment to stabilize
triplet excitons. Moreover, afterglow colors are continuously tuned after loading different mass
RhB via energy transfer. The as prepared materials are used as RTP inks for fabricating 3D
printing and photopatterning for anti-counterfeiting and information encryption applications.

Introduction
Room-temperature phosphorescence (RTP) materials, due to large Stokes shift, long
lifetime, and high signal-to-noise ratio, have attracted great attention in the applications of
biologic imaging, visual dictation, anti-counterfeiting and information encryption 1-9. Until now,
organic RTP materials with simple fabrication protocol, ease of processing, lower cost and
flexible mechanical properties have been developed to replace inorganic RTP materials, which
often contain high toxicity, high cost, poor-biocompatibility and complex fabrication processing
10-15. Generally, the generation of RTP requires the fulfillment of two prerequisites in organic
systems: (1) ISC from the lowest excited singlet state (S ) to a triplet state and (2) radiative
1
transitions from the lowest excited triplet state (T ) to the ground state (S ). Unfortunately,
1 0
inefficient ISC and triplet excitons quenching directly result in low efficient RTP, largely restricting
the development of RTP materials in the fields of optoelectronics 16. Strategies to develop high-
performance organic RTP materials include heavy-atom or lone-pair electron heteroatom effect
to strengthen SOC interactions for efficient ISC 17-20; crystalline engineering, host-guest
inclusion, matrix rigidification and polymerization afford rigid surrounding environment to
stabilize triplet excitons for phosphorescence emission 21-27. Among these, polymerization is a
simple fabrication protocol and ease of processing to afford rigid environment to stabilize triplet
excitons 28-33. Significantly, polymerization enables diverse regulations of RTP characteristics
(intensity, lifetime and quantum yield) through gradually rigidity of surrounding environments,
which is beneficial for understanding the intrinsic mechanism of RTP 34-36. Specifically,
photocured materials that transfer from a liquid state to a solid state when irradiated with UV
light are acknowledged as a familiar type of polymerization system 37, 38. However, photocured
RTP system requires phosphorescent chromophore and photo-initiator simultaneously,
increasing the stability and complexity of the whole system. Moreover, photo-initiator happens
photochemical reaction and may generate adversely factors to quench RTP emission from
phosphorescent chromophore. Several groups have reported photocured RTP materials. From
example, Chen et al. reported photocured RTP materials using a combination of lignosulfonate,
acrylamide, and ionic liquid with an emission lifetime of 110 ms and phosphorescence quantum
yield of 11.04% 39. Chen et al. also reported a solvent free system consisting 2-hydroxyethyl
acrylate, urethane dimethacrylate for converting lignin into RTP materials, with an emission
lifetime of 202.9 ms and humidity/water-resistant performance 40. Ma et al. reported
cycloaliphatic epoxy resin materials by utilizing three phosphors as hydrogen stripping initiators
and the obtained polymer systems perform optimally in terms of photocuring property,
mechanical property, and solvent resistance with controllable RTP emission 41. Comfortingly,
some photocured RTP systems have been developed, albeit with limited RTP performance.
Therefore, it is of an urgent demand to develop high-performance photocured RTP systems
integrating with phosphorescent chromophores and photo-initiators.

Naphthalimide is a hydrogen stripping photo-initiator and often requires the cooperation of
tertiary amines as proton donor to increase efficiency and stability 42, however, tertiary amines
severely suppress the optical properties of naphthalimide according to nonradiative decay of S
1
state, which are induced by photoinduced electron transfer (PET) effect 43. Nonradiative decay
of S state severely restricts ISC process, and largely limited generates triplet excitons for
1
phosphorescence emission. Therefore, in the naphthalimide system, a productive strategy is to
introduce a photophysical process to inhibit PET, thereby enabling more S excitons to undergo
1
ISC to generate triplet excitons for phosphorescence emission, and meanwhile retaining photo-
initiating ability. Herein, we introduced tertiary amines into naphthalimide (NDIAM) to
simultaneously act as phosphorescent chromophore and photo-initiator. Specifically, NDIAM
generates radicals to polymerize acrylic acid (AA), and acrylamide (AM) upon UV irradiation. As
a result, NDIAM is immobilized in the rigid microenvironment to generate robust RTP with water
and organic solvents resistance, long lifetime of 389.58 ms and high phosphorescence quantum
yield of 17.83% (Figure 1). Significantly, carboxyl group can bind onto the lone-pair electrons of
tertiary amine in NDIAM through proton transfer hydrogen-bonds (PTHBs), 44 which play as
following roles: (1) inhibit nonradiative decay of S state induced by PET; (2) increase SOC
1
values to promote ISC; (3) cooperate with intermolecular hydrogen-bonds affording rigid
microenvironment to stabilize triplet state excitons. Control experiments, such as photo-
polymerizing different ability of proton donating monomer (styrene, methacrylate, methyl
methacrylate, hydroxyethyl acrylate, and AA; photo-copolymerizing these monomers with AA;
dispersing NDIAM into PVA with or without acid, they all show yellow afterglows when NDIAM
meets with acid, which illustrates PTHBs playing a crucial role in regulating RTP characteristic.
This work provides an efficient method to achieve high-performance RTP in photocured system
and has a great potential in application of 3D printing and photopatterning.

Results
The naphthalimide derivative bearing tertiary amine group was successfully synthesized
using N, N-dimethylethylenediamine and 1,8-naphthalic anhydride, and named as NDIAM
(Supplementary Figs. S1) 45. The structure and purity were confirmed by ¹H NMR, 13C NMR, MS
and HPLC spectroscopic analyses (Supplementary Figs. S2-5, Supplementary Table 1). NDIAM
exhibits absorption characteristics in the UV-vis spectra range in 200-400 nm, confirming its
capacity to absorb 365 nm UV light and thereby enabling its utilization in subsequent steps
(Supplementary Fig. S6). The ESR spectrum shows silently signal before 365 nm UV light
irradiation. After 365 nm UV light irradiation for 20 s and 35 s (Power intensity: 300 mW/cm2),
obvious photochemical free radicals appear (Figure 2b) 46. These generated photochemical free
radicals can be used to initiate free radical polymerization of acrylic ester compounds. Therefore,
the mixed solution of NDIAM, AA, and AM (NDIAM-AA-AM, 1 mg NDIAM, 400 μL AA and 500
mg AM) are continuously exposed to UV light for photocuring (P-AA-AM). The photocuring
process is monitored by FT-IR, and the double bond conversion rate reaches ~ 91.80% after
365 nm UV light irradiation for 40 s (Figure 2c, Power intensity: 300 mW/cm2) 41. Increasing the
content of NDIAM (from 1 mg to 3 mg, AA and AM remain unchanged), UV photocured time for
the double bond conversion rate reaching maximum is shorten to 25 s (Supplementary Fig. S7).
To demonstrate the generation of free radicals during the photocuring process, 5,5-dimethyl-1-
pyrroline N-oxide (DMPO) was incorporated into the photocuring formulation as a free radical
scavenger, with a control experiment conducted in its absence. As anticipated, in the presence
of DMPO, no polymerization was observed after 3 minutes of UV irradiation. In contrast, when
DMPO is absent, NDIAM-AA-AM fully photocured under UV irradiation for 30 s (Supplementary
Fig. S8). To understand the reaction, the precursor solution of NDIAM-AA-AM was analyzed by
1H NMR before and after UV irradiation. The results show that the signal of the double bond
decrease, indicating that the photopolymerization occurs SSupplementary Fig. S9). In addition,
P-AA-AM demonstrates high transparency across the visible spectrum, high mechanical
strength, abundant intermolecular H-bonds interactions and amorphous molecular packing
structure (Supplementary Fig. S10). Glass transition temperature of P-AA-AM is 173.83 oC
(Supplementary Fig. S11). Followingly, the photophysical properties during photocured process
are systematically explored. NDIAM-AA-AM exhibits no RTP emission before photocuring
(Supplementary Figs. S12, 13). This is attributed to the high nonradiative decay rate in the liquid
environment around NDIAM, thereby causing RTP quenching 47. However, both RTP intensity
and lifetime sharply enhance with the extension of photocuring time (from 0 to 50 s) (Figure 2d-
2g), which are caused by a decrease in nonradiative decay with gradually increased rigid
microenvironment. Upon photocuring process, P-AA-AM achieves a prominent transformation
from the no afterglow to a bright 3 s yellow afterglow (Figure 2a). As such, lifetime increases to
389.58 ms (τ ), and phosphorescence quantum yield reaches as high as 17.83% (φ ) after
p p
photocuring for 50 s (Supplementary Fig. S14). When temperature lowered from 298K to 77 K,
phosphorescence intensity varied greatly, which is due to the nonradiative decay is greatly
suppressed (Supplementary Fig. S15). The influence of mass of NDIAM on phosphorescent
intensity and lifetime was also investigated. 0.01, 0.1, 1, 5, and 10 mg NDIAM were used to
photo-polymerize AA and AM. Phosphorescence intensity and lifetime reach a maximum at 1
mg NDIAM (Supplementary Fig. S16). It could be concluded that excess NDIAM resulted in
aggregation-caused quenching and energy dissipation 14. It’s worth mentioned that P-AA-AM
shows high-performance RTP with simultaneously high φ and long τ , which is a big challenge
p p
to achieve in photocured organic RTP field.

Conformingly, P-AA-AM showed robust RTP characteristic with water and organic solvents
resistance, which had rarely been observed for similar systems. Specifically, 233.61 ms long
lifetime, strong phosphorescence intensity and 1.5 s yellow afterglow are still observed when it
immerses in water for 210 min. After it immerses in water for 240 min, RTP lifetime decreases
to 93.70 ms, and yellow afterglow disappears (Figure 2h and 2i; Supplementary Fig. S17). The
RTP intensity and lifetime of P-AA-AM can restore to its original state after removing the water
(Supplementary Fig. S18). To understand the phenomenon, the contact angle and the surface
tension of P-AA-AM were measured (SupplementarPy Fig. S19). The value of contact angle and
the surface tension are 63.2° and 21.6 mN/m, indicating the characteristic of hydrophilicity. This
is because the water molecules form H-bonds with the surface carboxyl and amido bond in P-
AA-AM. Such interactions induced formation of dense molecular networks, decelerating water
molecules entering the network. As a result, the triplet excitons are well protected in P-AA-AM
and RTP emission is stable when the sample is immersed into water. The stability of P-AA-AM
is further investigated in organic solvents, RTP lifetime and intensity is not compromised when
it is immersed into different organic solvents, such as, n-Hexane, dimethyl formamide (DMF),
dichloromethane (DCM), methyl tert-butyl ether (MTBE), tetrahydrofuran (THF) and ethyl alcohol
(EtOH) for 45 days (Figure 2j; Supplementary Fig. S20). As a result, robust RTP with water and
organic solvents resistance is successfully achieved.

To get more insight into mechanism of photocured robust RTP of P-AA-AM, series of control
experiments were designed. Firstly, NDIAM is dissolved into different proton donating ability of
ethylene monomer, such as styrene (St), methacrylate (MA), methyl methacrylate (MMA),
hydroxyethyl acrylate (HEA), and AA (named as NDIAM-St, NDIAM-MA, NDIAM-MMA, NDIAM-
HEA and NDIAM-AA, respectively). St, MA, MMA, and HEA did not have active hydrogen atom
to bind onto the lone-pair electrons of tertiary amine. All these solutions form solid film on 2×2
cm glass (named as P-St, P-MA, P-MMA, P-HEA and P-AA) under 365 nm UV light irradiation.
1.5 s yellow afterglow is only observed in P-AA after removal 365 nm UV light (Figure 3a,
Supplementary Fig. S21); P-St, P-MA, P-MMA and P-HEA show no afterglow appearance
(Figure 3a). The double bond conversion rates reach ~ 22.22%, 66.03%, 84.44%, 69.07%, and
61.78% in P-St, P-MA, P-MMA, P-HEA, and P-AA, respectively, after 365 nm UV light irradiation
for 300 s (Supplementary Fig. S22). The prompt and delayed spectra of P-AA shows much
higher fluorescence and phosphorescence intensity than that of P-St, P-MA, P-MMA and P-HEA
(Figure 3b; Supplementary Fig. S23a). The lifetime decay curve of P-AA is used to certificate
RTP and shows long lifetime of 156.79 ms. The lifetime decay curve of P-St, P-MA, P-MMA and
P-HEA are 23.26, 21.45, 40.25, and 48.21 ms, respectively, which are much shorter than that of
P-AA (Figure 3c). The phosphorescence quantum yield of P-AA is 12.46%, is also much higher
than that of P-St, P-MA, P-MMA and P-HEA (0.87%, 0.51%, 0.56% and 1.09%, respectively)
(Figure 3d; Supplementary Fig. S24 and Table 2). Together with phosphorescence intensity,
phosphorescence lifetime and phosphorescence quantum yield, P-AA shows the best RTP
performance among these polymers. These results indicate that PET quenches RTP
performance in P-St, P-MA, P-MMA, and P-HEA, however, carboxyl of P-AA form PTHBs with
tertiary amine of NDIAMA to suppress nonradiative decay of S
1
state induced by PET. Meanwhile,
PTHBs and intermolecular H-bonds immobilize NDIAM in P-AA and stabilize triplet excitons,
thereby resulting in the appearance of the best RTP performance among these homopolymers.
Next, we use AA to photo-copolymerize with St, MA, MMA and HEA (named as P-AA-St, P-
AA-MA, P-AA-MMA, and P-AA-HEA, respectively) to elucidate PTHBs playing a crucial role in
regulating RTP performance. After removal 365 nm UV light irradiation, bright yellow afterglows
are all obtained in P-AA-St, P-AA-MA, P-AA-MMA, and P-AA-HEA film (Figure 3a). The delayed
spectra of P-AA-St, P-AA-MA, P-AA-MMA and P-AA-HEA show phosphorescence peaks at 550
and 600 nm (delay time = 1 ms) (Figure 3e) and exhibit sharply enhanced fluorescence and
phosphorescence intensity when compared with that of P-St, P-MA, P-MMA, and P-HEA
(Supplementary Fig. S23b and Supplementary Figs. S25-28). P-AA-St, P-AA-MA, P-AA-MMA,
and P-AA-HEA also exhibit prolonged RTP lifetime of 81.90, 198.24, 246.32, and 248.26 ms,
respectively (Figure 3f and 3g), (3.52 times for P-AA-St, 9.24 times for P-AA-MA, 6.12 times for
P-AA-MMA and 5.15 times for P-AA-HEA) (Supplementary Figs. S25-28) and enhanced
phosphorescence quantum yield of 2.15%, 3.43%, 4.77%, and 7.71%, respectively (4.21 times
for P-AA-St, 9.82 times for P-AA-MA, 9.48 times for P-AA-MMA and 6.72 times for P-AA-HEA,
respectively) (Supplementary Figs. S25-28). The double bond conversion rate reaches ~
77.08%, 90.96%, 85.44%, and 88.73% in P-AA-St, P-AA-MA, P-AA-MMA, and P-AA-HEA,
respectively, after 365 nm UV light irradiation (Supplementary Fig. S29, Supporting Information).
P-AA-St and P-St were selected to test time-resolved fluorescence, the excited-state lifetime in
P-AA-St was longer than that of P-St (Fig. 3h-3j; Supplementary Fig. S30), indicating that PTHBs
between acid-amine in P-AA-St effectively suppressed nonradiative S decay, thereby resulting
1
in the appearance of sharply enhanced phosphorescence lifetime and phosphorescence
quantum yield. In addition, the phosphorescence intensity, phosphorescence lifetime and
phosphorescence quantum yield of PL-AA-St, P-AA-MA, P-AA-MMA, and P-AA-HEA are lower
than that of P-AA-AM. This is because carboxyl and amido bond in P-AA-AM form stronger
intermolecular H-bonds, providing a more rigid microenvironment that effectively immobilizing
NDIAM motion to stabilize triplet excitons for phosphorescence emission.

Polyvinyl alcohol (PVA) serves as an ideal matrix owing to its abundant intermolecular H-
bonds for stabilizing triplet excitons, and has achieved rapid development in the field of RTP 48-
51. We dispersed 1 mg NDIAM into without or with carboxyl compounds (such as DMF, butyric
acid (BuA), propionic acid (PA), AA, acetic acid (AcA), and benzoic acid (BA)), then quickly
poured into 100 mg/mL PVA water solutions and dripped coating for film formation (named as
NDIAM-DMF/PVA, NDIAM-BuA/PVA, NDIAM-PA/PVA, NDIAM-AA/PVA, NDIAM-AcA/PVA, and
NDIAM-BA/PVA). NDIAM-DMF/PVA shows weak fluorescence and no afterglow, however,
added carboxyl compounds samples all exhibit strong blue fluorescence and yellow afterglow,
lasting for more than 1 s (Supplementary Fig. S31). The phosphorescence intensity of added
carboxyl compounds samples is significantly increased when compared with that of NDIAM-
DMF/PVA (Supplementary Fig. S32a). The lifetime of NDIAM-DMF/PVA can’t be fitted due to
low phosphorescence intensity, however, the lifetime decay curve of NDIAM-BuA/PVA, NDIAM-
PA/PVA, NDIAM-AA/PVA, NDIAM-AcA/PVA, and NDIAM-BA/PVA show long lifetime of 119.05,
179.20, 200.42, 222.10 and 274.96 ms, respectively (Supplementary Fig. S32b). To further
investigate the role of acids in regulating RTP performance, phosphorescence properties of
NDIAM-DMF/PVA and NDIAM-AA/PVA under vacuum and low-temperature conditions are
conducted. Under vacuum condition, phosphorescence intensity and lifetime of NDIAM-
DMF/PVA are too low to detect; strong phosphorescence intensity and 210.18 ms lifetime are
obtained in NDIAM-AA/PVA (Supplementary Fig. S33). It was not oxygen that quenched the
phosphorescence of NDIAM-DMF/PVA. Under low-temperature condition, NDIAM-AA/PVA
shows higher phosphorescence intensity and longer lifetime than that of NDIAM-DMF/PVA
(Supplementary Figs. S34, 35). These results indicate that PTHBs between acid-amine
promoting triplet formation and stabilizing triplet state for phosphorescence emission.
Protonated NDIAM was prepared by adding HCl into NDIAM solution, and then evaporating
solvents (NDIAM-H). We doped NDIAM-H into γ-cyclodextrin (γ-CD) and polyacrylic acid (PAA).
Stronger phosphorescence intensity and longer lifetime of NDIAM-H/PAA than that of NDIAM-
H/γ-CD are obtained, indicating that physical effect of matrix rigidification also play an important
role in regulating RTP performance (Supplementary Fig. S36). Consequently, high-performance
RTP can be realized by the combinations of PTHBs and intermolecular hydrogen bonds, which
facilitate triplet formation and stabilize triplet state for phosphorescence emission.

Mechanism for PTHBs Regulated RTP Performance
To investigate the mechanism of PTHBs regulated RTP performance, the absorption, FTIR and
1H NMR of NDIAM before and after adding AA solution were carried out. The absorption peak
at ~ 235 nm exhibits gradually reduced trend upon adding AA into NDIAM MeOH solution
(Supplementary Fig. S37). Upon adding NDIAM and triethylamine (TEA) into AA solution, the
vibration peaks of the hydroxyl at 2992 cm-1 and the carbonyl at 1694 cm-1 in the carboxyl
weaken; while the vibration peaks of the asymmetric and symmetric the carboxylate at 1541 cm-
1 and 1355 cm-1 appear (Supplementary Fig. S38). The hydrogen atoms in methyl group of
NDIAM, exhibit significant chemical shift upon adding AA (Supplementary Fig. S39). These
changes upon NDIAM meeting with AA, show the formation of PTHBs between the tertiary
amine and carboxyl groups. We also carried out a series of theoretical calculations between
various homopolymers and NDIAM. All molecular conformations were optimized and vibrational
frequency analyses were performed via the Gaussian 09 program at the B3LYP/6-31G(d,p) level
of theory. The electrostatic surface potential (ESP) analysis indicates that tertiary amine and
carbonyl of NDIAM show strong negative electrostatic potential (-31.98 and -34.91 kcal/mol,
respectively), carboxyl group of PAA show positive ESP values (62.19 kcal/mol), which indicating
strong intermolecular interactions with NDIAM (Figure 4a; Supplementary Fig. S40) 52.
According to the independent gradient model based on Hirshfeld partition (IGMH) analysis
(Figure 4b; Supplementary Figs. S41-43), the intermolecular interactions in
NDIAM/homopolymers are dominated by attractive interactions and van der Waals interaction
53. For NDIAM/PAA, the carboxyl groups of PAA can form strong H-bonds by proton transfer with
tertiary amine in NDIAM, which can influence energy level of tertiary amine; there also exist H-
bonds between the carboxyl groups of PAA and carbonyl of NDIAM. To gain a clearer
understanding of proton transfer regulating energy alignment and orbital characteristics, we
employ the Gaussian 09 software package and adopt the B3LYP/6-311G* basis set to perform
density-functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The HOMO
and LUMO of trimethylamine (TMA) overlap with that of naphthalimide without tertiary amine
(NA), indicating PET would happen between TMA and NA moiety. NDIAM exhibits weak
fluorescence and phosphorescence, due to S excitons adopting nonradiative decay induced by
1
PET (Supplementary Fig. S44). Following, energies of frontier orbitals of TMA interact with
various monomers (TMA-St, TMA-MA, TMA-MMA, TMA-HEA and TMA-AA) and NA are
calculated. The HOMO and LUMO energy of TMA-St, TMA-MA, TMA-MMA and TMA-HEA are
still overlapped with than that of NA, indicating these monomers can’t suppress nonradiative
decay of S state induced by PET. However, AA can effectively bind onto the lone-pair electrons
1
of TMA through PTHBs, leading to significantly affect the energy level distribution of TMA.
The
HOMO and LUMO energy of TMA-AA include that of NA, exhibiting nonradiative decay of S
1
state induced by PET are effectively suppress, leading to more S excitons to undergo ISC to
1
generate triplet excitons (Figure 4c). To demonstrate their differences in ISC, energy levels and
SOC constants are calculated by ORCA4.2.0 (Figure 4d; Supplementary Fig. S45;
Supplementary Table 5). Within the ± 0.3 eV range of S energy level, NDIAM/PAA exhibits the
1
probability of ISC to T -T states with large SOC constants of 0.20, 0.30, 0.78, 1.59, 0.81, and
5 9 S
0.21 cm-1, respectively. While, the other homopolymer chains exhibit less ISC channels (T for
2
NDIAM, NDIAM/PSt, and NDIAM/PMA; T and T for NDIAM/PHEA), and small SOC values
2 3
(0.18 cm-1 for NDIAM; 0.16 cm-1 for NDIAM/PSt, 0.48 cm-1 for NDIAM/PMA; 0.15 and 0.16 cm-1
for NDIAM/PHEA). The increasing ISC channels and larger SOC values in NDIAM/PAA
demonstrate PTHBs largely promote ISC for enhancing RTP performance. The natural transition
orbitals (NTOs) of NDIAM in PSt, PMAL, PHEA, and PAA are also calculated (Figure 4e). For S
1
state as example, the hole and the electron distribute on PAA in NDIAM/PAA; while the hole and
the electron distribute on NDIAM in NDIAM, NDIAM/PSt, NDIAM/PMA and NDIAM/PHEA. The
complete transfer of the hole and the electron verify a charge transfer of S
1
state in NDIAM/PAA,
which promotes ISC from S to T and larger ISC constant (k ) (Supplementary Fig. S46) 54.
1 m ISC
The k of NDIAM/PAA is as large as 6.29×107, which is higher than that of NDIAM/PSt,
ISC
NDIAM/PMA and NDIAM/PHEA (Supplementary Fig. S47; Supplementary Table S2, 3).
Meanwhile, the hole and the electron of T in NDIAM/PAA are also distributed into PAA,
1
corresponds to a charge transfer T state, leading to a small phosphorescent nonradiative decay
1
constant (k ) (Supplementary Fig. S48). The k of P-AA is 5.07 s-1and is much lower than
p,nr p,nr
that of P-St, P-MA, P-MMA and P-HEA. τ of P-AA could be extended by the equation of τ = 1
p p
/ (k + k ) 55. As a result, the introduction of PTHBs in NDIAM photocured materials can inhibit
p,r p,nr
nonradiative decay of S state induced by PET and increase SOC values to promote ISC,
1
leading to long lifetime RTP.

Tunable Afterglow through Triplet-to-Singlet Förster Resonance Energy Transfer
The wide phosphorescence band of P-AA-AM provides a significant advantage when it is
used as an energy donor to prepare afterglow materials through the triplet-to-singlet FRET (TS-
FRET) process (Figure 5a). RhB is selected as the ideal acceptor due to the highly overlapped
UV absorption spectrum with the phosphorescence spectrum of P-AA-AM (Figure 5b) 56. A FRET
system with RhB as an energy acceptor and P-AA-AM as an energy donor is constructed (P-
AA-AM/RhB, weight ratio of 1:1). As anticipated, the RTP characteristics of P-AA-AM/RhB are
significantly different from those of P-AA-AM alone. Specifically, P-AA-AM/RhB exhibits
fluorescence emission near ~614 nm, which is attributed to RhB. Additionally, P-AA-AM/RhB
displays a delayed RTP emission at around ~610 nm, with a lifetime of approximately 241.58
ms (Figure 5c). Interestingly, strong delayed emission is observed under indirect excitation at
365 nm, but no obvious delayed emission of RhB was observed under direct excitation at 550
nm (Figure 5d). These results indicate that P-AA-AM/RhB undergoes an efficient TS-FRET
process from P-AA-AM to RhB, and the afterglow of P-AA-AM/RhB in the long wavelength region
can be achieved by the delayed fluorescence of RhB. To further understand the energy transfer
process, we measure phosphorescence properties of P-AA-AM/RhB after adding different
concentrations of RhB in the system, including the changes of fluorescence spectra,
phosphorescence spectra and phosphorescence lifetime (Figure 5e; Supplementary Figs. S49,
50). These results show that with change of RhB weight ratio, the delayed spectra intensity at
550 nm of P-AA-AM/RhB system gradually weakens and finally disappears completely upon
increasing weight ratio 1:10 (P-AA-AM/RhB). At the same time, the position of delayed spectra
is gradually red-shifted from 550 nm to 614 nm. The reason is that RhB molecules are prone to
aggregate with lower energy levels at higher concentrations, resulting in red-shifted delayed
emission peak. The coordinates of different weight ratio P-AA-AM/RhB = 1/0, 1/0.1, 1/0.5, 1/1,
1/3, 1/5, and 1/10 are (0.44, 0.47), (0.52, 0. 43), (0.56, 0.41), (0.58, 0.38), (0.63, 0.36), (0.64,
0.35) and (0.65, 0.34), respectively, and exhibit gradually red-shifted emission from yellow to
red region (Figure 5f). The time-resolved photoluminescence analysis of P-AA-AM/RhB delayed
emission peak at 550 nm (λ =465 nm) revealed a significant reduction in the average lifetime,
ex
from 373.50 ms to 108.40 ms (Figure 5g). The decreased lifetime provides strong evidence for
the non-radiative FRET from the triplet state of P-AA-AM donor to the singlet state of the RhB
acceptor in the P-AA-AM/RhB system through the TS-FRET mechanism. The TS-FRET
efficiency (φ ) was calculated as 14.8%, 19.0%, 35.3.%, 59.1.%, 68.0% and 71.0% based on
FRET
the equation φ = 1-τ/τ , where τ and τ represented phosphorescence lifetimes of energy
FRET 0 0
donor before and after energy transfer (Figure 5h; Supplementary Table 4). Therefore, a large
range of color adjustment can be conveniently obtained with afterglow, which is conducive to
expand their practical applications in many fields.

3D Printing and Photopatterning Applications
The precursor solution of NDIAM-AA-AM has good fluidity and can be adaptively changed
according to the shape of the curing mold. We pour the precursor solution into the mold of
different shapes, and in-situ exposure under UV irradiation, we can easily prepare a variety of
desired shapes. Specifically, we first inject the precursor solution into the silica gel mold, and
obtain a P-AA-AM thin layer with yellow RTP after UV irradiation. The P-AA-AM thin layer will
be superimposed and solidified layer by layer through photocuring technology, and finally a 3D
bulk material with a pentagonal flower morphology will be constructed. The material exhibits
blue fluorescence under 365 nm UV excitation, and exhibits bright yellow afterglow after the UV
light turned off (Figure 6a; Supplementary Fig. S51). Similarly, we use the red afterglow of P-
AA-AM/RhB system to make a 3D bulk material with red RTP emission (Figure 6b). We can also
prepare complex 3D bulk materials with both yellow and red RTP emission by layer-by-layer
photocuring approach (Figure 6c). P-AA-AM and P-AA-AM/RhB for UV-curable coating of cotton
yarn (Figure 6d). Specifically, the woven shape of the cotton yarn is immersed in a solution
containing the precursor. Then, the treated yarn was subjected to UV irradiation. After P-AA-AM
or P-AA-AM/RhB treatment, the coated yarns show yellow or red afterglow emission,
respectively. Encouraged by this, these RTP yarns are used to generate cotton thread for anti-
counterfeiting purposes using commercial machines. Under 365 nm UV irradiation, the blue and
orange red on P-AA-AM cotton and P-AA-AM/RhB cotton are clearly visible. When UV light is
turned off, the P-AA-AM/RhB cotton thread remains red afterglow. P-AA-AM cotton thread
retains yellow afterglow.
To further demonstrate its application potential, polyurethane acrylate resin is added to the
precursor solution of NDIAM-AA-AM or NDIAM-AA-AM/RhB to adjust the viscosity, and ink
materials are suitable for photopatterning. The detailed steps of photopatterning process are
illustrated in Figure 6e. The material can be precisely patterned into diverse designs after UV
irradiation and water developing, thereby yielding a patterned RTP (Figure 6f). It is worth noting
that the substrate can be flexibly varied, such as glass, PVC film, and PET film. On the PVC film,
butterfly pattern can be freely curled and bent without sacrificing its luminescent properties
(Supplementary Figs. S52-54). Especially, school emblem and high-precision micro-graphics in
the form of QR codes with RTP characteristic is successfully obtained on a glass substrate
(Figure 6g and 6h).

Methods
Photocuring of P-AA-AM
A mixture containing 400 μL of acrylic acid (5.83 mmol), 500 mg of acrylamide (7.03 mmol), and
1 mg of NDIAM was heated to 60 °C until it formed a homogeneous solution. Subsequently, the
solution was subjected to photocuring under a 365 nm UV light with an intensity of 300 mW/cm2
for 50 s.

Photocuring of P-AA-AM/RhB
A solution was prepared by mixing AA (400 μL, 5.83 mmol), AM (500 mg, 7.03 mmol), NDIAM
(1 mg, 0.00373 mmol), and RhB (3 mg, 0.00626 mmol). This mixture was heated to 60 °C until
it achieved homogeneous solution. Subsequently, the homogeneous solution was subjected to
photocuring by exposure to 365 nm UV light with an intensity of 300 mW cm⁻² for 1 minute. After
1 minute, P-AA-AM/RhB material with red RTP was obtained.

Preparation of Photolithography Ink Materials
To meet the viscosity requirements for photolithography, the precursor solution of NDIAM-AA-
AM was mixed with 150 mg of polyurethane acrylate resin. The mixture was then uniformly
dispersed using magnetic stirring to form a homogeneous solution, yielding a photolithography
ink material with yellow RTP emission. Similarly, we incorporated 150 mg of photopolymerizable
resin into the P-AA-AM/RhB precursor solution to formulate a red RTP photolithographic ink
material.

Preparation of 3D bulk RTP materials
The 3D bulk material with RTP emission was prepared by layer-by-layer photocuring method.
Specifically, the precursor solution of NDIAM-AA-AM was poured into a silicone mold, and after
photopolymerization, a thin layer with yellow RTP emission was obtained. Repeating this
operation yields a 3D bulk yellow RTP material. Similarly, using the precursor solution of NDIAM-
AA-AM/RhB results in a 3D bulk red RTP material. Moreover, by alternately stacking and curing
the two precursors solutions layer by layer, a 3D bulk material with multicolor RTP was fabricated.

Preparation of afterglow cotton yarn
The cotton yarn was immersed in a precursor (AA 400 μL, AM 500 mg, NDIAM 1 mg) solution.
Then, the treated cotton thread was placed in 365 nm UV light for 3 min to obtain a yellow
afterglow cotton thread. In order to obtain the afterglow cotton line emitted by red afterglow, 3
mg RhB solution can be added to the precursor solution for the same operation.

Preparation of Photolithography RTP Patterns
The photolithography ink material is uniformly coated on the substrate, and then covered with a
layer of PVC film to form a thin and uniform photolithography ink layer between the substrate
and the PVC film. Subsequently, 365 nm UV light is used to expose the designated area of the
photolithography ink layer through a mask of a specific shape. After 80 s exposure, the
unexposed ink was removed by developing with water, the underexposed ink was still retained
after water developing. Finally, the desired pattern is formed on the substrate.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Recommendation: May be suitable for Nature Communications after minor revisions.\nThe authors report photocured room-temperature phosphorescence materials and naphthalimide simultaneously acts as\nphosphor and photo-initiator. The resulting naphthalimide is tightly restricted in in-situ formed crosslinked matrix to achieve\nrobust RTP with a long lifetime of 389.58 ms, high phosphorescence quantum yield of 17.83%, water and organic solvents\nresistance. Carboxyl can bind onto the lone-pair electrons of tertiary amine through PTHBs, inhibiting non-irradiation\ntransition of S1 induced by PET; increasing SOC matrix elements values to promote ISC; affording rigid microenvironment to\nstabilize triplet excitons. Moreover, the afterglow colors are continuously tuned from yellow to red after loading different mass\nRhB via energy transfer. The as prepared materials are used as phosphorescent inks for fabricating 3D printing and\nphotopatterning applications. This work is conceptually promising and the authors have demonstrated it through a range of\nexperiments. I recommend the publication of this manuscript after minor revision.\nQuestion 1. The authors declared that “NDIAM are optimized with simplified homopolymers through molecular dynamics\nsimulation”. The calculations details and methods should be added in the experiments section.\nQuestion 2. The authors should indicate the purity of NDIAM with HPLC analysis.\nQuestion 3. In Figure 3a, AA photo-copolymerizes with St, MA, MMA and HEA, why the afterglow photographs of P-AA-St,\nP-AA-MA and P-AA-MMA are inhomogeneous?\nQuestion 4. The authors only provide the double bond conversion rate in P-AA-AM. The double bond conversion rates for\nother photo-polymerization systems also should be added, which can better explain the different phosphorescent properties\nbetween these polymers.\nQuestion 5. P-AA-AM showed robust RTP with water resistance within 240 min. When removing the water, can RTP\nproperty restore to its original state?\nQuestion 6. The authors should include more refs in introduction to show the benefits of (Controlled) radical polymerization\nfor the synthesis of RTP polymers.\nQuestion 7. As controlled radical polymerization could synthesize linear polymers or polymer networks with better uniformity,\nwhat will happen if controlled Radical polymerization was employed for the 3D-printing of RTP polymers?", "reviewer_2": "In the manuscript entitled “Proton Transfer Regulated Photocured Robust Room-Temperature Phosphorescence from\nNaphthalimide”. Authors have designed photocured robust RTP materials with long lifetime and high phosphorescence\nquantum yield. The present system is also highly resistant towards water and organic solvents, as clear from long afterglow\neven in the presence of water. Authors also have performed extensive investigation to reveal PTHBs regulated RTP\nsystems, such as photo-polymerize monomers without active hydrogen atom, photo-copolymerize these monomers with AA,\nand mixed with PVA. Moreover, yellow to red afterglow colors are continuously tuned after loading different mass RhB via\nTS-FRET strategy. Using these properties, the as prepared materials are used as RTP inks for fabricating 3D printing and\nphotopatterning for anti-counterfeiting and information encryption applications. The manuscript has enough novelty and\nsuitable to publish in this journal.\nHowever, the author should address the following points.\n1.Authors use 1 mg photo-initiator to photo-polymerize monomers and has good RTP performance. What is the effect of\ndifferent content photo-initiator on RTP property?\n2.In line 177-179, authors have claimed that the “the stability of P-AA-AM is further investigated in organic solvents and RTP\nlifetime is not compromised when it is immersed into different organic solvents”. Please provide phosphorescence spectra\nafter organic solvents treatment to further demonstrate the stability of RTP in P-AA-AM.\n3.The basic properties of P-AA-AM need to be investigated, such as FTIR, molecular weight, XRD, Tg, Tm and mechanical\nproperty characterization.\n4.In Figure 5c, the insert pictures are too small to be clearly seen. Please provide high resolution pictures.\n5.Authors should mention the delay time used for delayed emission spectra in Figure 2d, 2e, and 3b.", "reviewer_3": "The manuscript presents a novel approach to photocurable room-temperature phosphorescence (RTP) materials using\nnaphthalimide derivatives as both photoinitiators and phosphorescent chromophores. The RTP is convincing and can be\ntuned from yellow to red by varying RhB content, enabling applications in 3D printing, and information encryption. However,\nseveral mechanistic claims require stronger experimental support. Some of the major comments are listed below;\n1. Similar strategies using hydrogen-bonded hosts to activate 1,8-naphthalimide RTP have been reported (e.g., Chem.\nCommun., 2022, 58, 3641; DOI:10.1039/d2cc00474g). The authors should cite this work and clearly explain how their\nsystem and mechanistic insights differ.\n2. The authors propose that PTHB between the tertiary amine and carboxyl groups plays a central role in regulating RTP.\nHowever, this claim requires direct experimental evidence. Please provide spectroscopic confirmation, such as FT-IR, XPS\nN 1s or pH-dependent absorption, to distinguish PTHB from ordinary hydrogen bonding.\n3. The manuscript claims that PTHB suppresses PET and nonradiative S₁ decay. This should be experimentally verified.\nTechniques such as time-resolved fluorescence or transient absorption spectroscopy could directly demonstrate\nsuppression of nonradiative pathways and increased ISC efficiency.\n4. Can the authors further demonstrate that the acidic environment enhances triplet exciton generation and stabilization?\nFor example, comparison of oxygen sensitivity, and low-temperature phosphorescence between acidic and non-acidic\nsystems in addition to the phosphorescence lifetimes would clearly clarify whether the acid–amine interaction promotes triplet\nformation, stabilizes the triplet state, or both.\n5. The current results do not clearly distinguish the chemical effect of protonation from the physical effect of matrix\nrigidification. Please decouple these effects, e.g., by examining protonated NDIAM in rigid but non-polymeric matrices, or in\nflexible acidic polymers.\n6. The manuscript frequently uses “nonradiative transition” to describe S₁ decay pathways. Please replace this with the\nstandard term “nonradiative decay.”\n7. Minor corrections such as, use the proper symbol for µ, not “u,” for all volume measurements (e.g., µL), carefully check\nspelling and grammar throughout the manuscript. Also, Figures S7 (and related spectra) would be more informative if all\nrelevant NMR spectra are presented in a single figure for direct comparison.\nOverall, the work is promising, but mechanistic claims need stronger experimental support. I recommend major revision to\naddress the points above. The manuscript will be significantly improved once these issues are addressed."}, "author_response": "Question 1. The authors declared that “NDIAM are optimized with simplified homopolymers through molecular dynamics simulation”. The calculations details and methods should be added in the experiments section.\nResponse: Thank you for pointing out this. All molecular conformations optimized and\nvibrational frequency analyses were performed via the Gaussian 09 program at the\nB3LYP/6-31G(d,p) level of theory. Excited-state calculations were carried out using the\nORCA 4.2.0 program at the PBE0/def2-SV(P) level. Analysis of the electrostatic\npotential surfaces (ESPs), independent gradient model based on Hirshfeld partition\n(IGMH) analysis, and natural transition orbital (NTO) analysis for the singlet (S₁) and\ntriplet (T₁) excited states were completed with the Multiwfn_3.8_dev program, and the\ncorresponding plots were generated using the VMD 1.9.3 program. The calculations\ndetails and methods have been added in the revised manuscript (Page 15, Line 14-16;\nSupplementary Information, Page S5, Line 4-13).\nQuestion 2. The authors should indicate the purity of NDIAM with HPLC analysis.\nResponse: We have performed HPLC to ensure the high purity of NDIAM compounds\nand have been added in the revised manuscript. (Supplementary Fig. 4; Supplementary\nTable 1).\nQuestion 3. In Figure 3a, AA photo-copolymerizes with St, MA, MMA and HEA, why\nthe afterglow photographs of P-AA-St, P-AA-MA and P-AA-MMA are inhomogeneous?\nResponse: Probably, the energy of UV light is not uniform, thereby leading to afterglow\nphotographs of P-AA-St, P-AA-MA and P-AA-MMA are inhomogeneous. We re-test\nthe photo-polymerization of AA with St, MMA, and MA and homogeneous afterglow\nphotographs have been updated in the revised manuscript (Page 14, Figure 3a;\nSupplementary Fig. S24-S27).\nQuestion 4. The authors only provide the double bond conversion rate in P-AA-AM.\nThe double bond conversion rates for other photo-polymerization systems also should\nbe added, which can better explain the different phosphorescent properties between\nthese polymers.\nResponse: Thank you very much for your valuable comment. The double bond\nconversion rate reaches ~ 22.22%, 66.03%, 84.44%, 69.07%, and 61.78% in P-St, P-\nMA, P-MMA, P-HEA, and P-AA, respectively, after 365 nm UV light irradiation for\n300 s (Power intensity: 300 mW/cm2). The conversion rate of P-AA is not the highest\nin these polymers, however, P-AA shows the best RTP performance, which are due to\nproton transfer hydrogen-bonds and intermolecular H-bonds immobilize NDIAM and\nstabilize triplet excitons. These contents have been added in the revised manuscript\n(Page 10, Line 11-14; Supplementary Fig. 21 and Supplementary Fig. 28).\nQuestion 5. P-AA-AM showed robust RTP with water resistance within 240 min. When\nremoving the water, can RTP property restore to its original state?\nResponse: The RTP lifetime and intensity of P-AA-AM can restore to its original state\nafter removing the water (Supplementary Fig. 17).\nQuestion 6. The authors should include more refs in introduction to show the benefits\nof (Controlled) radical polymerization for the synthesis of RTP polymers.\nResponse: Thank you for your comments. The related reference about controlled\nradical polymerization for the synthesis of RTP polymers have been added in the revised\nmanuscript (Page 3, Line 2; Page 29, Line 23-29, Reference: 31-33).\nQuestion 7. As controlled radical polymerization could synthesize linear polymers or\npolymer networks with better uniformity, what will happen if controlled Radical\npolymerization was employed for the 3D-printing of RTP polymers?\nResponse: Thank you very much for your valuable comment. Controlled radical\npolymerization could synthesize linear polymers or polymer networks with better\nuniformity, however, it has very high requirements for the catalyst and is sensitive to\nthe environment (H O and O ), which can’t directly apply in 3D-printing in current\n2 2\nstage. If controlled radical polymerization is employed for the 3D-printing RTP\npolymers, the process parameters of 3D printing and RTP property is pretty stable and\ngood repeatability.\nQuestion 1. Authors use 1 mg photo-initiator to photo-polymerize monomers and has\ngood RTP performance. What is the effect of different content photo-initiator on RTP\nproperty?\nResponse: The influence of the doping mass of NDIAM on phosphorescent intensity\nand lifetime was also investigated. 0.01, 0.1, 1, 5, and 10 mg NDIAM were used to\nphoto-polymerize AA and AM. Phosphorescence intensity and lifetime reach a\nmaximum at doping 1 mg NDIAM. It could be concluded that excess photo-initiator\nresulted in energy dissipation and aggregation-caused quenching. The related contents\nhave been added in the revised manuscript (Page 7, Line 16-21; Supplementary Fig.\n15).\nQuestion 2. In line 177-179, authors have claimed that the “the stability of P-AA-AM\nis further investigated in organic solvents and RTP lifetime is not compromised when\nit is immersed into different organic solvents”. Please provide phosphorescence spectra\nafter organic solvents treatment to further demonstrate the stability of RTP in P-AA-\nAM.\nResponse: Phosphorescence intensity after organic solvents treatment is not\ncompromised when compares with the initial state (Supplementary Fig. 19).\nQuestion 3. The basic properties of P-AA-AM need to be investigated, such as FTIR,\nmolecular weight, XRD, T , T and mechanical property characterization.\ng m\nResponse: Thank you very much for your valuable comment. The FTIR, XRD, T ,\nand\ng\nmechanical property characterization have been tested. Many solvents (water, THF,\nDMF and DMSO) can’t dissolved P-AA-AM even heated to 180 ℃. It might be due to\nthe formation of 3D polymer network during the photo-polymerization process. So,\nmolecular weight can’t be investigated at the current stage. XRD pattern indicates that\nP-AA-AM adopts amorphous form and with no definite T . The related contents have\nm\nbeen added in the revised manuscript (Page 6, Line 29; Page 7, Line 1-3; Supplementary\nFigs. 9-10).\nQuestion 4. In Figure 5c, the insert pictures are too small to be clearly seen. Please\nprovide high resolution pictures.\nResponse: Thank you for pointing out this. High resolution pictures have been updated\nin the revised manuscript (Page 21, Figure 5c).\nQuestion 5. Authors should mention the delay time used for delayed emission spectra\nin Figure 2d, 2e, and 3b.\nResponse: The delay time is 1 ms for delayed emission spectra in Figure 2d, 2e, and\n3b (Page 9, Line 6-8; Page 14, Line 4).\nQuestion 1. Similar strategies using hydrogen-bonded hosts to activate 1,8-\nnaphthalimide RTP have been reported (e.g., Chem. Commun., 2022, 58, 3641;\nDOI:10.1039/d2cc00474g). The authors should cite this work and clearly explain how\ntheir system and mechanistic insights differ.\nResponse: Thank you very much for your valuable comment. This work reports the\nroom-temperature phosphorescence of 1,8-naphthalimide was activated by doping it\ninto aromatic dicarboxylic acids (Chem. Commun., 2022, 58, 3641;\nDOI:10.1039/d2cc00474g). Abundant intermolecular hydrogen-bond network can be\nconstructed through interactions between carboxyl groups of aromatic dicarboxylic\nacids and imidyl groups of 1,8-naphthalimide, which can suppress the non-radiative\ndecay process to activate room-temperature phosphorescence. 1,8-naphthalimide doped\ninto other hosts, such as PVA, the RTP could also be activated (Macromol. Chem. Phys.\n2025, 226, 2400498). However, in our system, NDIAM exhibits no afterglow when\ndoped into PVA matrix, or photo-polymerize St, MA, MMA and HEA. Long lifetime\nRTP cannot be realized by intermolecular hydrogen bonds alone. Bright afterglows are\nobtained after adding acidic compounds into above systems. Together with time-\nresolved fluorescence, pH-dependent absorption, and theory calculations, proton-\ntransfer hydrogen bonds (PTHBs) between acid-amine are formed and play as\nfollowing roles: (1) inhibiting non-irradiation transition of S state induced by PET;\n1\n(2)\nincreasing SOC values to promote ISC; (3) providing a rigid microenvironment that\neffectively immobilizing NDIAM motion to stabilize triplet excitons for\nphosphorescence emission. We have cited this work in the revised manuscript (Page 29,\nLine 11-13, Reference 27).\nQuestion 2. The authors propose that PTHB between the tertiary amine and carboxyl\ngroups plays a central role in regulating RTP. However, this claim requires direct\nexperimental evidence. Please provide spectroscopic confirmation, such as FT-IR, XPS\nN 1s or pH-dependent absorption, to distinguish PTHB from ordinary hydrogen\nbonding.\nResponse: Thank you very much for your valuable comment. NDIAM solution (2×10-\nmaking NDIAM and AA at different molar weight. The absorption peak at ~ 235 nm\nexhibits gradually reduced trend upon adding AA (Supplementary Fig. 36). AA,\nNDIAM-AA (150 mg NDIAM and 600 μL AA), and triethylamine (TEA)-AA (200 μL\nTEA and 600 μL AA) of FTIR were also tested. Upon adding NDIAM and triethylamine\n(TEA) into AA solution, the vibration peaks of the hydroxyl at 2992 cm-1and the\ncarbonyl at 1694 cm-1 in carboxyl weaken; while the vibration peaks of the asymmetric\nand symmetric the carboxylate at 1541 cm-1 and 1355 cm-1appear (Supplementary Fig.\n37). The hydrogen atoms in methyl group of NDIAM, exhibits significant chemical\nshift upon adding AA (Supplementary Fig. 38). Together with pH-dependent absorption,\nFT-IR, and 1H NMR, these changes upon NDIAM meeting with AA, show the\nformations of proton transfer hydrogen-bonds between the tertiary amine and carboxyl\ngroups. The contents have been added in the revised manuscript (Page 15, Line 2-13;\nSupplementary Figs. 36-38).\nQuestion 3. The manuscript claims that PTHB suppresses PET and nonradiative S₁\ndecay. This should be experimentally verified. Techniques such as time-resolved\nfluorescence or transient absorption spectroscopy could directly demonstrate\nsuppression of nonradiative pathways and increased ISC efficiency.\nResponse: Thank you very much for your valuable comment. Time-resolved\nfluorescence tests revealed the differences in the luminescence dynamics of P-AA-St\nand P-St. Both P-AA-St and P-St exhibited double-exponential decay characteristics,\nbut their excited-state lifetime distributions were significantly different. For P-AA-St,\nthe fluorescence lifetime (τ₁, 1.77 ns, accounting for 45.29%) was significantly longer\nthan that of P-St (τ₁, 0.87 ns, accounting for 76.01%), and its long lifetime component\n(τ₂) contribution was as high as 54.71%, much higher than 23.99% of P-St. These results\nindicate that the excited-state lifetime in P-AA-St was significantly prolonged, and\nnonradiative S₁ decay is effectively suppressed, thereby enhancing the fluorescence\nemission. The contents have been added in the revised manuscript (Figure 3h-3j; Page\n11, Line 22-27; Supplementary Fig. 29).\nQuestion 4. Can the authors further demonstrate that the acidic environment enhances\ntriplet exciton generation and stabilization? For example, comparison of oxygen\nsensitivity, and low-temperature phosphorescence between acidic and non-acidic\nsystems in addition to the phosphorescence lifetimes would clearly clarify whether the\nacid-amine interaction promotes triplet formation, stabilizes the triplet state, or both.\nResponse: Thank you very much for your valuable comment. Under vacuum condition,\nin non-acidic systems (NDIAM/PVA), phosphorescence intensity and lifetime are too\nlow to detect; in acidic system (NDIAM-AA/PVA), strong phosphorescence intensity\nand 210.18 ms lifetime are obtained, which are longer than that of in air (Supplementary\nFig. 32). Consequently, it was not oxygen that quenched the phosphorescence of\nNDIAM/PVA. Under low-temperature condition (77K), NDIAM/AA/PVA shows\nhigher phosphorescence intensity and longer lifetime than that of NDIAM/PVA\n(Supplementary Figs. 33, 34). These results indicate that proton transfer hydrogen-\nbonds between acid-amine promoting triplet formation and stabilizing triplet state for\nphosphorescence emission. Related contents have been added in the revised manuscript\n(Page 12, Line 21-29; Page 13, Line 1-3).\nQuestion 5. The current results do not clearly distinguish the chemical effect of\nprotonation from the physical effect of matrix rigidification. Please decouple these\neffects, e.g., by examining protonated NDIAM in rigid but non-polymeric matrices, or\nin flexible acidic polymers.\nResponse: Thank you very much for your valuable comment. Protonated NDIAM was\nprepared by adding hydrogen chloride solution into NDIAM DCM solution, and\nprecipitate (NDIAM-H) was obtained. We doped NDIAM-H into γ-cyclodextrin (γ-CD)\nand PAA. NDIAM-H/PAA shows higher phosphorescence intensity and longer lifetime\nthan that of NDIAM-H/γ-CD, indicating that physical effect of matrix rigidification\nalso play an important role in regulating RTP performance (Page 13, Line 3-10;\nSupplementary Fig. 35).\nQuestion 6. The manuscript frequently uses “nonradiative transition” to describe S₁\ndecay pathways. Please replace this with the standard term “nonradiative decay.”\nResponse: Thank you for pointing out this. We have replaced \"nonradiative transition\n\"with \"non-radiative decay\" in the revised manuscript (Page 2, Line 2; Page 3, Line 30;\nPage 4, Line 1, 16; Page 7, Line 6, 9, and 16; Page 10, Line 28; Page 16, Line 6, 11 and\n15; Page 17, Line 9 and 13).\nQuestion 7. Minor corrections such as, use the proper symbol for µ, not “u,” for all\nvolume measurements (e.g., µL), carefully check spelling and grammar throughout the\nmanuscript. Also, Figures S7 (and related spectra) would be more informative if all\nrelevant NMR spectra are presented in a single figure for direct comparison.\nOverall, the work is promising, but mechanistic claims need stronger experimental\nsupport. I recommend major revision to address the points above. The manuscript will\nbe significantly improved once these issues are addressed.\nResponse: Thank you for pointing out this. We have modified these numerous grammar\nerrors and carefully polishing the language in the revised manuscript (Page 6, Line 12;\nPage 24, Line 22; Page 25, Line 3). Relevant NMR spectra are presented in a single\nfigure for direct comparison (Supplementary Fig. 8)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed all my questions. The current manuscript is recommended to be accepted.", "reviewer_2": "The present work can be published in Nature Communications.", "reviewer_3": "The reviewers' comments have been addressed satisfactorily, and the manuscript is recommended for acceptance"}, "author_response": "Dear Reviewers,\nThank you very much for your positive review and for agreeing to accept our\nmanuscript. We are truly grateful for your time and valuable feedback, which\nhas greatly contributed to the quality of our work.\nWe confirm that we have carefully reviewed the final version of the manuscript.\nAll the revisions and improvements suggested during the review process have\nbeen implemented, and we believe the manuscript now meets the journal's\nstandards.\nOnce again, thank you for your support and for helping us bring this work to\npublication. We look forward to the next steps in the publication process.\nSincerely,\nBing Fang, Meizhen Yin, and Yuhua Dai"}]

Decision letter