Through-space charge transfer delayed fluorescence in tris(triazolo)triazine donor–acceptor copolymers

Abstract

Donor–acceptor materials containing tris(triazolo)triazine (TTT) acceptors have recently gained attention as green to deep-blue fluorophores exhibiting thermally activated delayed fluorescence (TADF). Concurrently, polymers exhibiting through-space charge transfer (TSCT) between donor and acceptor monomers have been reported as high-performance TADF materials, yet few TSCT polymers have been reported to date. Here we describe the synthesis of copolymers comprised of TTT acceptor and 9,9-dimethyl-9,10-dihydroacridine donor monomers by ring-opening polymerization. These non-conjugated polymers have molecular weights up to 68.0 kDa and exhibit blue-green TSCT TADF in solution and the solid state. The photophysical properties of these materials are described herein, and density functional theory with noncovalent interaction analysis is used to explain the TSCT behaviour of the donor–acceptor pairs.

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Introduction

Charge transfer (CT) interactions between electron donors and acceptors are fundamental to optoelectronics, enabling advanced, tailorable materials for display technology, chemical sensing, bio-imaging, and photocatalysis.^1–6 Among CT-based materials, those that show thermally activated delayed fluorescence (TADF) have gained significant attention in the past decade.^7–11 Such materials are useful as sensitizers and emitters in organic light-emitting diode (OLED) technology, since they are capable of efficiently harvesting both singlet and triplet excitons generated by electrical excitation.^7,12 TADF materials are capable of achieving close to 100% internal quantum efficiency in OLEDs due to reverse intersystem crossing (RISC), which converts excitons from a material's lowest-energy triplet excited state (T₁) to the singlet state (S₁) by thermal upconversion.^7,13 To facilitate this process, TADF materials must exhibit a small energy gap (typically <0.2–0.3 eV) between S₁ and T₁, termed ΔE_ST.^14–16

Most TADF materials rely on through-bond CT (TBCT) occurring via covalent bonds between electron donor and acceptor units, however there is recent interest in TADF that occurs via through-space charge-transfer (TSCT) between donor and acceptor.^17–19 While the TBCT design often leads to materials with increased conjugation length and red-shifted emission, TSCT can retain blue emission by keeping the π-systems of the donor and acceptor separated, which can also increase the rate of RISC.^8,17,20 Amongst strategies to access TSCT interactions, donor–acceptor copolymers have attracted significant attention since the emissive units are held in close proximity by the polymer backbone, facilitating CT and allowing for the tuning of photophysical properties via polymer morphology.^19,21,22 Polymers also offer advantages in optoelectronics due to their compatibility with low-cost solution processing techniques such as spin-coating and inkjet printing, as well as their potential for use in flexible devices.^22–24 Efforts to explore diverse donor–acceptor combinations for TSCT TADF, as well as to better understand the TSCT process, thus represent promising avenues for research.^21,25

TSCT systems using 1,3,5-triazine acceptors have been extensively studied in both small molecules and polymers with diverse morphologies.^22,25–28 In 2017, Wang and coworkers synthesized a blue-emitting TSCT system for TADF using a non-conjugated polyethylene backbone, which demonstrated an external quantum efficiency of 12% and sky blue emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.176, 0.269) (Fig. 1).²⁹ The same group expanded their work to triazine motifs decorated with various electron-withdrawing substituents to shift emission from blue to red.²² They also developed triazine-acridine TSCT interactions in one norbornene monomer, improving face-to-face interaction and oscillator strength.³⁰ In 2019, our group investigated triazine-based TSCT in bottlebrush polymers using ring-opening metathesis polymerization (ROMP), with interface dependent and aggregation induced TADF.³¹ Later in 2021, we further explored a series of donor–acceptor acrylic copolymers, including triazine acceptors, to investigate the requirements for efficient TSCT in polymers based luminescent materials.³² While these examples have provided a deeper understanding of TSCT-based TADF polymers and their applications, exploration of new donor–acceptor interactions can further expand fundamental knowledge and applications.

Fig. 1 Outline of current and previous work on through-bond interactions in TTT frameworks, and TSCT polymers based on triazine motifs.

In recent years, [1,2,4]-triazolo-[1,3,5]-triazine (TTT) has emerged as a π-extended analog of 1,3,5-triazine, with weaker electron withdrawing ability for deeper blue emission and better solution processability (Fig. 1).^33–36 Several TTT-based small molecules have been reported with blue emission, non-linear optical properties for biological applications, and external quantum efficiencies >20% in OLEDs.^34,36–38 Consequently, we thought to explore TSCT polymer systems based on the TTT acceptor motif, given the electronic similarity and potentially enhanced luminescent properties compared to previously reported 1,3,5-triazine TSCT materials.

Herein, we report the synthesis of TTT-containing donor–acceptor copolymers using ROMP. To our knowledge, this is the first example of a polymer incorporating TTT motifs. Despite the abundance of nitrogen lone pairs in TTT that could coordinate to the catalyst used in ROMP, polymers with 10 or 25 mol% acceptor were synthesized, with dispersities as low as 1.26. A monomer based on 10-dihydro-9,9-dimethylacridine (ACR) was selected as the electron donor due to its weak donating ability, which results in blue to green emission, and previous studies which point towards ACR as an efficient donor in TSCT systems.^21,29,30,32 We avoided the use of even weaker donors, such as carbazole, which would give poor HOMO–LUMO separation and thus a lack of TADF properties, or stronger donors, such as phenoxazine, which would lead to bathochromic shifts that are undesirable for blue emission. Most notably, TSCT TADF emission is demonstrated for the first time in TTT-based materials.

Synthesis

We first synthesized the acceptor monomer TTT-NB in six steps (Scheme 1; for ¹H and ¹³C{¹H} NMR spectra see Fig. S1–S13†). TTT-3PhI was first prepared according to previously reported procedures,³⁷ then a Sonogashira coupling using tert-butyloxycarbonyl (Boc)-protected propargylamine afforded TTT-2PhI-Boc. The two remaining aryl iodides were then capped with octyne groups to afford TTT-2Oct-Boc; the alkyl groups were previously successfully used in our studies with highly π-conjugated TADF materials to improve solubility, with marginal changes to photophysical properties.³⁹ These alkyl chains were also included to enhance the solubility of the material for the remainder of the monomer synthesis, as well as the polymerization itself. After deprotection of the Boc group to afford a primary amine (TTT-2Oct-NH₂), the norbornene-appended TTT monomer TTT-NB was obtained via condensation with cis-5-norbornene-exo-2,3-dicarboxylic anhydride. The donor monomer ACR-NB was synthesized by coupling a exo-norbornene-bearing propanoic acid (NB-CO₂H) with an benzyl alcohol functionalized with a 9,10-dihydro-9,9-dimethylacridine donor.

Scheme 1 (A) Synthesis of the acceptor monomer TTT-NB. (B) Synthesis of the donor monomer ACR-NB. (C) Polymerization of copolymers via ROMP.

With the donor (ACR-NB) and acceptor (TTT-NB) monomers at hand, Grubbs’ third-generation catalyst (G3) was used to prepare random donor–acceptor copolymers via ROMP. Since previous reports point towards lower doping of acceptor units to be beneficial for efficient TSCT emission,^21,29,32 we first prepared TTT₁-co-ACR₃ with three to one donor to acceptor ratio, respectively. After 3 h, the reaction reaches 99% conversion by ¹H NMR with a dispersity (Đ) of 1.38 measured by gel permeation chromatography (GPC). Previous studies in our group have shown that reducing temperature can be effective in improving dispersity when bulky monomers are employed in ROMP.^2,40 In this case, however, minimal conversion was observed after 6 hours when the reaction was repeated at −20 °C. The reaction did proceed when conducted at 0 °C, but did not reach full conversion after 24 hours and did not improve the dispersity of the polymer.

To understand the impact of each monomer on the polymerization and to improve understanding of the photophysical properties of the copolymer, we then attempted the polymerization of the homopolymers of TTT-NB and ACR-NB. The polymerization of ACR-NB proceeded to full conversion to give poly(ACR) with Đ of 1.10 within 3 hours (Table 1). Conversely, homo-polymerization of TTT-NB led to no conversion after 24 hours, indicating that a high concentration of TTT-NB hinders polymerization either due to coordination of the imine motifs on TTT to G3, or due to the large size of the monomer. Tracking the polymerization of TTT₁-co-ACR₃ by ¹H NMR (Fig. S25†) indicates that the presence of TTT-NB does not lead to preferential incorporation of ACR-NB to the polymer backbone, as both monomers are consumed at a similar rate, giving a random copolymer. With the above results in mind, we also prepared the copolymer TTT₁-co-ACR₉ with a donor : acceptor ratio of one to nine. As anticipated, lowering the doping percentage of TTT successfully improved the control over ROMP to give a lower dispersity of 1.26.

Table 1 Properties of polymers

Entry	M n target (kDa)	M n obs  (kDa)	Đ	Donor	Acceptor	Donor^b (%)	Acceptor^b (%)
				DPAvg	DPAvg
a For poly(ACR), measured directly by triple detection GPC; for copolymers, measured by GPC relative to poly(ACR). b Determined using ^1H NMR in CD2Cl2.
poly(ACR)	53.3	56.5	1.10	106	—	100	—
TTT1-co-ACR3	61.1	62.0	1.38	79	24	77	23
TTT1-co-ACR9	56.3	68.0	1.26	108	12	90	10

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Despite the rigid core of TTT, all three polymers show excellent solubility in common organic solvents (toluene, CH₂Cl₂, THF). Additionally, all polymers exhibited similar glass transition temperatures (T_g) around 138–143 °C and thermal stability up to 333–338 °C as determined by differential scanning calorimetry (Fig. S14†) and thermogravimetric analysis (Fig. S15†), respectively.

Photophysical and electrochemical properties

The UV-visible absorption and photoluminescence spectra in toluene are depicted in Fig. 2A and S16.† The absorption maxima of the donor monomer, acceptor monomer, and their corresponding copolymers TTT₁-co-ACR₃ and TTT₁-co-ACR₉ all lie between 289 nm to 297 nm. The monomer TTT-NB emits in the UV region with an emission maximum at 350 nm, while the donor polymer poly(ACR) has emission maxima at 358 nm and 451 nm. In contrast, a broad, red-shifted and featureless emission likely arising from donor–acceptor charge-transfer is observed for TTT₁-co-ACR₃ and TTT₁-co-ACR₉, at 530 nm and 527 nm, respectively (Table 2). This red-shifted emission is absent when the monomers TTT-NB and ACR-NB are simply mixed in toluene, indicating that the polymeric backbone plays a critical role in TSCT emission by holding the donor and acceptor in close proximity (Fig. S18†). Emission spectra displayed no clear trends as a function of solvent polarity (Fig. S17†), revealing an interplay between TSCT emission and locally excited emission from the ACR monomers that varied with solvent. As both the TTT and ACR monomers exhibit significantly different solubilities in various organic solvents, we suspect that the changes in emission band intensity are due to differences in aggregation within the polymer chains as a function of solvent (Table 2).

Fig. 2 (A) Emission spectra of materials in toluene solution (0.01 mg mL⁻¹, λ_ex = 313 nm), with prompt fluorescence (PF) and through space charge transfer (TSCT) emission highlighted. (B) Photoluminescence decays of copolymers under inert vs. aerated conditions (IRF = instrument response function).

Table 2 Photophysical properties of materials in toluene (0.01 mg mL⁻¹)

Entry	λ ^maxabs (nm)/ε (10^4 cm^−1 M^−1)	λ ^Inertem (nm)	CIE (x, y)^Inert	Φ ^air/Φ^Inert	τ ^air/τ^Inert (ns)	τ ^aird/τ^Inertd (μs)
a The two values indicate the lifetimes at 358 and 451 nm, respectively.
TTT-NB	297/8.2	350	(0.18, 0.07)	0.81/0.95	1.3/1.3
poly(ACR)	289/2.0	358, 451	(0.16, 0.15)	0.01/0.01	3.7, 7.5/3.7, 7.5^a
TTT1-co-ACR3	290/3.6	349, 530	(0.31, 0.45)	0.05/0.09		0.33/0.83
TTT1-co-ACR9	289/1.5	348, 527	(0.31, 0.45)	0.01/0.06		0.28/1.3

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The photoluminescence quantum yield (Φ) of the copolymers TTT₁-co-ACR₃ and TTT₁-co-ACR₉ increased when carried out under nitrogen vs. air, indicating the involvement of the triplet state in their emission pathway (Table 2). Photoluminescence (PL) decays were then analyzed in toluene using time-correlated single-photon counting (TCSPC). The lifetime of the acceptor monomer TTT-NB and poly(ACR) were found to be short-lived and insensitive to inert conditions, with lifetimes of 1.3 ns and 7.5 ns, respectively (Fig. S18A†). However, the TSCT emission of the copolymers exhibits a longer lifetime, which is enhanced under inert conditions, suggesting TADF behavior (Fig. 2B and Table 2). Additional control experiments with the 1 : 3 ratio of ACR-NB (donor) TTT-NB (acceptor) monomers were conducted in inert toluene, and the lack of long-lived delayed emission indicates that polymerization induces face-to-face interactions between the donor and acceptor moieties, giving rise to TSCT and consequently TADF in solution (Fig. S18B†).

The emission properties of solid films of TTT₁-co-ACR₃, TTT₁-co-ACR₉, TTT-NB, and poly(ACR) were also studied (Fig. 3A). TSCT emission bands were observed for both TTT₁-co-ACR₃ and TTT₁-co-ACR₉ at 475 nm and 468 nm, respectively (Table 3), which are red-shifted compared to the donor or acceptor emission in the solid state, but blue-shifted compared to the copolymers in toluene (Fig. 2A). To investigate the PL lifetime, both TCSPC and multi-channel scaling analyses were employed (Fig. S19†). The results indicate that poly(ACR) and TTT-NB exhibit short lifetimes in the nanosecond range without any delayed emission. In contrast, both TTT₁-co-ACR₃ and TTT₁-co-ACR₉ show long-lived emission under inert conditions, up to 113 μs and 150 μs, respectively. Temperature-dependent lifetime measurements from 100 K to 298 K also demonstrate the emergence of long-lived delayed emission upon heating to ambient temperatures, providing further evidence of TADF (Fig. 3B).

Fig. 3 (A) Emission of materials in the solid state (all measured in neat film, except for TTT-NB and ACR-NB which were measured in 1 wt% PMMA). (B) Temperature dependent PL decay of copolymers. λ_exc = 313 nm.

Table 3 Photophysical properties of materials in the solid state

Entry	λ ^Inertem (nm)	Φ ^air	τ ^air/τ^Inert (ns)	τ ^aird/τ^Inertd (μs)
All measurements conducted using neat films, except for TTT-NB which was measured in 1 wt% poly(methyl methacrylate) (PMMA).
TTT-NB	383	0.15	1.7/1.7	—
poly(ACR)	441	0.02	22/22	—
TTT1-co-ACR3	475	0.01	—	75/113
TTT1-co-ACR9	468	0.04	—	81/150

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Time-gated phosphorescence and fluorescence spectra were also collected to measure ΔE_ST from the onset energies of the fluorescence and phosphorescence emission bands (Fig. S20†). Both copolymers exhibits a very small ΔE_ST with TTT₁-co-ACR₉ having the value of 0.09 eV, which matches closely with the theoretical calculations (vide infra). However, in solid-state measurements, it is challenging to eliminate the risk of interpolymer chain interactions and the contribution of donor–donor exciplex emission. Nevertheless, the TSCT emission observed exclusively for the copolymers in solution at low concentrations provides strong evidence of the TADF properties of these materials (Fig. 2B).

The electronic properties of the materials were studied using cyclic voltammetry (CV) (Fig. S21†). The optical gap (E_gap) was determined from Tauc plots, which were generated using UV-Vis measurements (Fig. S22†). The HOMO energy of the donor and the LUMO energy of the acceptor were found to match previously reported values, at −5.16 eV and −2.45 eV, respectively (Table 4). However, due to the low level of doping and the relatively insoluble nature of the TTT acceptor, we could not observe the reduction of TTT in the copolymers.

Table 4 Experimental and theoretical electronic properties of materials

Entry (eV)	E ^ox (eV)	E ^red	HOMO/LUMO^b^,^c (eV)	E ^optgap ^d (eV)
a Measured in 1,2-diflurobenzene relative to ferrocene/ferrocenium. b HOMO = −(E^ox + 4.8 eV). c LUMO = −(E^red + 4.8 eV). d Calculated using a Tauc plot of the UV-Vis spectrum in toluene. Note that E^optgap will be larger than the HOMO–LUMO gap here, as the latter arises from two different monomers.
TTT-NB	—	−2.35	−6.20/−2.45	3.75
poly(ACR)	0.358	—	−5.16/−1.34	3.82
TTT1-co-ACR3	0.358	—	−5.16/−2.45	3.76
TTT1-co-ACR 9	0.358	—	−5.16/−2.45	3.80

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Theoretical calculations

To further understand the photophysical properties of the TSCT copolymers, dimers of TTT and ACR were modelled by DFT. These calculations reveal differences between interacting and noninteracting donor and acceptor moieties (Fig. 4A) and allow for comparison of the face-to-face donor–acceptor interactions with portions of the polymer where face-to-face interactions are impossible. Using Gaussian 16,⁴¹ both dimer conformations were optimized at the M06-2X/def2-SVP level of theory,^42,43 and the optimized geometries were verified as minima via frequency analysis. The noncovalent interactions (NCI) present in both the interacting and noninteracting dimer were analyzed using the Multiwfn program.^44,45 Then, TDDFT with an optimally tuned screened (OT-S) range separated hybrid functional was employed, utilizing the Tamm-Dancoff approximation (TDA) to improve prediction of triplet excitation energies.⁴⁶ In OT-S functionals, correct asymptotic decay of the exchange–correlation potential is ensured by nonempirical tuning of three free parameters: ω, the range separation parameter, and α and β, which control the amount of Hartree–Fock and DFT exchange in the short- and long-range regimes (details in ESI†).^47–49 The first 50 singlet and triplet vertical excitation energies for each dimer conformation were calculated with TDA-TDDFT using ORCA at the OT-S-LC-PBE/def2-TZVP/CPCM(toluene) level of theory.^50,51 Hole–electron analyses of these excitations were performed using the Multiwfn program.⁵²

Fig. 4 (A) Stick diagrams of the noninteracting and interacting TTT–ACR dimers, with the ACR donor shown in turquoise and the TTT acceptor shown in purple (hydrogen atoms and alkyl chains omitted). (B) NCI analysis plots and (C) visualization of the hole and electron densities for the S₁ states, with the calculated S₁ excitation energies and ΔE_ST values indicated.

The absorbance maxima of both conformers are predicted to be approximately the same, with a maximum of 299 nm for the interacting dimer, and 297 nm for the noninteracting dimer (Fig. S23†). This is in good agreement with the experimental absorbance wavelengths of 290 nm and 289 nm for TTT₁-co-ACR₃ and TTT₁-co-ACR₉, respectively. In both the interacting and noninteracting cases, the absorbance maximum does not correspond to the S₁ state, since these have zero or near-zero oscillator strengths, but instead correspond to a higher singlet state representing a local excitation into the TTT moiety (Fig. S23†). This result is also in line with the observed prompt fluorescence of copolymers at 350 nm arising from the TTT moiety (alongside TSCT emission at 530 nm, Fig. 2).

Although emission energies could not be predicted due to difficulty modelling the excited state conformations of these dimers, the significant red shifting of the S₁ state for the interacting dimer (403 nm) compared to the noninteracting dimer (311 nm) is consistent with the red shifted wavelength of the TCST emission observed experimentally. Additionally, the ΔE_ST in the noninteracting dimer is predicted to be quite large (0.91 eV), but NCI analysis indicates strong van der Waals interactions between the donor and acceptor in the interacting dimer that stabilize the S₁ state (Fig. 4B, C and S24†), resulting in significant reduction of the ΔE_ST (0.10 eV), and subsequently, TSCT-type TADF emission. In NCI analysis, the reduced density gradient (RDG) approaches zero for noncovalent interactions, with the strength of the noncovalent interaction indicated by the magnitude of the electron density (ρ) when the RDG approaches zero, and the nature of the interaction as attractive or repulsive determined by the sign of the second Hessian eigenvalue (λ₂). The value of sign(λ₂)ρ is colour-coded, with red indicating repulsive interactions such as steric interactions, green indicating weak interactions such van der Waals interactions, and blue indicating attractive interactions such as hydrogen bonding. The NCI analysis plot of the interacting dimer (Fig. 4B) shows the RDG approaching zero for very small values of ρ, consistent with the presence of van der Waals interactions, while the corresponding plot for the noninteracting dimer shows significantly weaker interactions in this region. This demonstrates that face-to-face interaction of the TTT and ACR moieties is required for TADF to occur, explaining why only the TSCT bands of the copolymers exhibit a delayed lifetime.

Conclusion

In this study, we have synthesized TTT-based donor–acceptor copolymers through ring-opening polymerization, resulting in non-conjugated polymers with dispersities below 1.26, molecular weights up to 68.0 kDa, and luminescence ranging from sky blue to green. Most notably, this work reveals the first observation of TSCT TADF in TTT-based donor–acceptor materials. Compared to previously reported triazine-based TSCT polymers, we observed a more red-shifted emission and similar lifetimes in solution (Scheme S1 and Table S1†). However, the photoluminescence quantum yield of the TTT copolymers was relatively low in comparison.^22,32 Efforts to enhance the photophysical properties of TTT-TSCT systems by improving the donor–acceptor interaction, increasing the solubility of the TTT monomers, using stronger donors paired with TTT to yield yellow to orange emission,³⁶ and limiting non-radiative decay pathways are ongoing in our laboratory, and may lead to TADF materials with application in OLEDs and as polymer-based probes for bioimaging.

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

The authors gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation for financial support of their work. R. H. thanks NSERC for a Canada Graduate Scholarship, K. B. thanks NSERC for a Vanier Canada Graduate Scholarship, and Z. M. H. is grateful for support from the Canada Research Chairs program. We gratefully acknowledge the Laboratory for Advanced Spectroscopy and Imaging Research (LASIR) for the use of photophysical instrumentation, the Digital Research Alliance of Canada for computational resources, as well as Prof. Scott Renneckar and Dr Sanaz Sabaghi for access to equipment for thermogravimetric analysis.

References

1. S. Weissenseel, N. A. Drigo, L. G. Kudriashova, M. Schmid, T. Morgenstern, K. H. Lin, A. Prlj, C. Corminboeuf, A. Sperlich, W. Brütting, M. K. Nazeeruddin and V. Dyakonov, J. Phys. Chem. C, 2019, 123, 27778–27784.
2. N. R. Paisley, S. V. Halldorson, M. V. Tran, R. Gupta, S. Kamal, W. R. Algar and Z. M. Hudson, Angew. Chem., Int. Ed., 2021, 60, 18630–18638.
3. J. Xu, J. Cao, X. Wu, H. Wang, X. Yang, X. Tang, R. W. Toh, R. Zhou, E. K. L. Yeow and J. Wu, J. Am. Chem. Soc., 2021, 143, 13266–13273.
4. D. Zhang and L. Duan, Nat. Photonics, 2021, 15, 173–174.
5. Y. X. Hu, J. Miao, T. Hua, Z. Huang, Y. Qi, Y. Zou, Y. Qiu, H. Xia, H. Liu, X. Cao and C. Yang, Nat. Photonics, 2022, 16, 803–810.
6. O. S. Wenger, Nat. Chem., 2020, 12, 323–324.
7. H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, Nature, 2012, 492, 234–238.
8. Y. Wada, H. Nakagawa, S. Matsumoto, Y. Wakisaka and H. Kaji, Nat. Photonics, 2020, 14, 643–649.
9. D. T. Yonemoto, C. M. Papa, C. Mongin and F. N. Castellano, J. Am. Chem. Soc., 2020, 142, 10883–10893.
10. G. Hong, X. Gan, C. Leonhardt, Z. Zhang, J. Seibert, J. M. Busch and S. Bräse, Adv. Mater., 2021, 33, 0935–9648.
11. S. M. Suresh, D. Hall, D. Beljonne, Y. Olivier and E. Zysman-Colman, Adv. Funct. Mater., 2020, 30, 1616–3010.
12. M. Hempe, N. A. Kukhta, A. Danos, M. A. Fox, A. S. Batsanov, A. P. Monkman and M. R. Bryce, Chem. Mater., 2021, 33, 3066–3080.
13. K. Goushi, K. Yoshida, K. Sato and C. Adachi, Nat. Photonics, 2012, 6, 253–258.
14. R. Huang, N. A. Kukhta, J. S. Ward, A. Danos, A. S. Batsanov, M. R. Bryce and F. B. Dias, J. Mater. Chem. C, 2019, 7, 13224–13234.
15. R. S. Nobuyasu, J. S. Ward, J. Gibson, B. A. Laidlaw, Z. Ren, P. Data, A. S. Batsanov, T. J. Penfold, M. R. Bryce and F. B. Dias, J. Mater. Chem. C, 2019, 7, 6672–6684.
16. T. Hosokai, H. Matsuzaki, H. Nakanotani, K. Tokumaru, T. Tsutsui, A. Furube, K. Nasu, H. Nomura, M. Yahiro and C. Adachi, Sci. Adv., 2017, 3, 1–10.
17. Y. Song, M. Tian, R. Yu and L. He, ACS Appl. Mater. Interfaces, 2021, 13, 60269–60278.
18. Q. Xue and G. Xie, Adv. Opt. Mater., 2021, 9, 2002204.
19. X. Yin, Y. He, X. Wang, Z. Wu, E. Pang, J. Xu and J. Wang, Front. Chem., 2020, 8, 2296–2646.
20. C. Li, Z. Ren, X. Sun, H. Li and S. Yan, Macromolecules, 2019, 52, 2296–2303.
21. S. Shao and L. Wang, Aggregate, 2020, 1, 45–56.
22. J. Hu, Q. Li, X. Wang, S. Shao, L. Wang, X. Jing and F. Wang, Angew. Chem., Int. Ed., 2019, 58, 8405–8409.
23. A. Arjona-Esteban and D. Volz, Highly Effic. OLEDs, 2018, 543–572.
24. E. V. Puttock, C. S. K. Ranasinghe, M. Babazadeh, J. Jang, D. M. Huang, Y. Tsuchiya, C. Adachi, P. L. Burn and P. E. Shaw, Macromolecules, 2020, 53, 10375–10385.
25. Q. Zheng, X.-Q. Wang, Y.-K. Qu, G. Xie, L.-S. Liao and Z.-Q. Jiang, npj Flexible Electron., 2022, 6, 83.
26. X. Tang, L.-S. Cui, H.-C. Li, A. J. Gillett, F. Auras, Y.-K. Qu, C. Zhong, S. T. E. Jones, Z.-Q. Jiang, R. H. Friend and L.-S. Liao, Nat. Mater., 2020, 19, 1332–1338.
27. D. Sun, C. Si, T. Wang and E. Zysman-Colman, Adv. Photonics Res., 2022, 3, 2200203.
28. X. Lv, Y. Wang, N. Li, X. Cao, G. Xie, H. Huang, C. Zhong, L. Wang and C. Yang, Chem. Eng. J., 2020, 402, 126173.
29. S. Shao, J. Hu, X. Wang, L. Wang, X. Jing and F. Wang, J. Am. Chem. Soc., 2017, 139, 17739–17742.
30. Q. Li, J. Hu, J. Lv, X. Wang, S. Shao, L. Wang, X. Jing and F. Wang, Angew. Chem., Int. Ed., 2020, 59, 20174–20182.
31. C. M. Tonge and Z. M. Hudson, J. Am. Chem. Soc., 2019, 141, 13970–13976.
32. J. Poisson, C. M. Tonge, N. R. Paisley, E. R. Sauvé, H. McMillan, S. V. Halldorson and Z. M. Hudson, Macromolecules, 2021, 54, 2466–2476.
33. R. Su, Y. Zhao, F. Yang, L. Duan, J. Lan, Z. Bin and J. You, Sci. Bull., 2021, 66, 441–448.
34. Z. Fang, S. Wang, J. Liao, X. Chen, Y. Zhu, W. Zhu and Y. Wang, J. Mater. Chem. C, 2022, 10, 4837–4844.
35. F. Hundemer, E. Crovini, Y. Wada, H. Kaji, S. Bräse and E. Zysman-Colman, Mater. Adv., 2020, 1, 2862–2871.
36. S. K. Pathak, Y. Xiang, M. Huang, T. Huang, X. Cao, H. Liu, G. Xie and C. Yang, RSC Adv., 2020, 10, 15523–15529.
37. R. Hojo, D. M. Mayder and Z. M. Hudson, J. Mater. Chem. C, 2021, 9, 14342–14350.
38. R. Hojo, D. M. Mayder and Z. M. Hudson, J. Mater. Chem. C, 2022, 10, 13871–13877.
39. D. M. Mayder, C. J. Christopherson, W. L. Primrose, A. S.-M. Lin and Z. M. Hudson, J. Mater. Chem. B, 2022, 10, 6496–6506.
40. Y. Nishihara, Y. Inoue, A. T. Saito, Y. Nakayama, T. Shiono and K. Takagi, Polym. J., 2007, 39, 318–329.
41. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, A. P. Raghavachari, K. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman and D. J. Fox, Gaussian16, Gaussian, Inc., Wallingford, CT, 2016.
42. Y. Zhao and D. G. Truhlar, Theor. Chem. Acc., 2008, 120, 215–241.
43. F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys., 2005, 7, 3297–3305.
44. T. Lu and F. Chen, J. Comput. Chem., 2012, 33, 580–592.
45. E. R. Johnson, S. Keinan, P. Mori-Sánchez, J. Contreras-García, A. J. Cohen and W. Yang, J. Am. Chem. Soc., 2010, 132, 6498–6506.
46. M. J. G. Peach, M. J. Williamson and D. J. Tozer, J. Chem. Theory Comput., 2011, 7, 3578–3585.
47. S. Bhandari, M. S. Cheung, E. Geva, L. Kronik and B. D. Dunietz, J. Chem. Theory Comput., 2018, 14, 6287–6294.
48. S. Bhandari and B. D. Dunietz, J. Chem. Theory Comput., 2019, 15, 4305–4311.
49. K. Begam, S. Bhandari, B. Maiti and B. D. Dunietz, J. Chem. Theory Comput., 2020, 16, 3287–3293.
50. F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci., 2012, 2, 73–78.
51. F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci., 2022, 12, e1606.
52. Z. Liu, T. Lu and Q. Chen, Carbon, 2020, 165, 461–467.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3py00325f

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