Thermally activated delayed fluorescence emitters with a LUMO-extended boron-containing acceptor for high-efficiency and long-lifetime blue OLEDs†

Jeong-Yeol Yoo‡ , Seung Wan Kang‡ , Tae Hoon Ha and Chil Won Lee *
Department of Chemistry, Dankook University, Cheonan 31116, Republic of Korea. E-mail: chili@dankook.ac.kr

First published on 12th August 2024

---

---

Introduction

A theoretical internal quantum efficiency of 100% can be achieved by leveraging the thermally activated delayed fluorescence (TADF) mechanism discovered by Prof. Adachi and his research team.^1–3 This outstanding theoretical efficiency can be attributed to the existence of a small energy gap, ΔE_ST, of <0.3 eV between the singlet and triplet exciton states. Consequently, a triplet exciton can transition to a singlet state through reverse intersystem crossing (RISC).

However, most TADF organic light-emitting diodes (OLEDs) exhibit triplet–triplet annihilation (TTA) and triplet–polaron annihilation (TPA) owing to the long lifetime of the delayed exciton state and intermolecular interactions.^4,5 According to various studies, TTA and TPA primarily influence the efficiency roll-off of OLEDs, i.e., the reduction in efficiency at 1000 cd m⁻² with respect to the maximum external quantum efficiency (EQE).^6,7 For TADF materials, the TTA and TPA processes are based on intermolecular electron exchange. Therefore, suppressing the intermolecular electron exchange is a possible strategy for inhibiting efficiency roll-off. In principle, by increasing the RISC rate constant (k_RISC) and shortening the lifetime of the T₁ exciton, the TTA and TPA processes can be mitigated.^8,9

The basic design of TADF molecules involves the incorporation of groups with electron-donating (donor) and electron-accepting (acceptor) characteristics to separate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions.^10–12 Electron donor–acceptor (D–A) or donor–acceptor–donor (D–A–D) molecules with a twisted structure can provide a small ΔE_ST and efficient RISC yield and induce an intramolecular charge-transfer (ICT) state.^13–15 Among the investigated TADF molecules designed by various strategies, the D–A–D structure facilitates rapid RISC through large spin–orbit coupling (SOC) matrix elements (SOCMEs).^16,17 Additionally, an increase in the horizontal transition dipole orientation (HTDO) ratio allows for the more efficient use of out-coupling, thus enhancing the EQE of the device as demonstrated in several studies.^18–20

Recently developed boron-based polycyclic aromatic hydrocarbons have received considerable attention because of their robust characteristics, such as high thermal and chemical stabilities, derived from flat structures that appropriately arrange boron and oxygen atoms within the molecule.^21,22 These hydrocarbons offer a wide range of structural variations for their application in optoelectronic systems.²³ 5,9-Dioxa-13b-boranaphtho[3,2,1-de]anthracene (DOBNA), which includes boron and oxygen, exhibits acceptor properties owing to the empty π-orbital in boron. Owing to its planar structure, resulting from its sp² hybridized orbital and high triplet exciton energy, DOBNA can achieve a high photoluminescence quantum yield (PLQY) and can be applied in blue OLED devices.^24–29

In this study, a DOBNA acceptor with extended π-conjugation was designed by introducing benzonitrile at the para position of boron. Extending the π-conjugation depolarizes the distribution of the frontier molecular orbitals (FMOs), which decreases the ΔE_ST, enhances the TADF characteristics, and increases the HTDO ratio, thereby enhancing out-coupling efficiency. Furthermore, a carbazole derivative, which is an electron donor for blue emitters, was also introduced, forming the D–A–D structure of [4-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-2,6-di(9H-carbazol-9-yl)benzonitrile], hereafter referred to as DOB-1. Consequently, tert-butyl [4-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-2,6-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)benzonitrile] and phenyl groups [4-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-2,6-bis(3,6-diphenyl-9H-carbazol-9-yl)benzonitrile], hereafter denoted by DOB-2 and DOB-3, respectively, were introduced at the weak 3,6 positions in the carbazole derivative to enhance its electron-donor characteristics. We expected these designs to suppress the TTA and TPA processes, delivering a high PLQY, fast RISC, and a large HTDO ratio. In turn, we anticipated enhanced efficiency and stability, potentially improving device efficiency and extending its lifetime. Indeed, as-synthesized DOB-2 and DOB-3 exhibited high PLQYs of 92% and 95%, respectively, along with a high RISC rate (∼10⁵ s⁻¹) and excellent HTDO ratios of 0.86 and 0.90. In addition, TADF OLED devices employing DOB-2 and DOB-3 demonstrated high maximum EQEs (EQE_MAX) of 23.6% and 28.7%, respectively. Furthermore, the OLED with DOB-3 showed a long lifetime (LT₅₀) of 1377 h at 2000 cd m⁻², signifying a low efficiency roll-off.

Results and discussion

Synthesis

All materials and reagents were purchased from commercial suppliers and used without further purification. The detailed materials, synthetic routes, and characterization data for the compounds, including the results of ¹H NMR spectroscopy, gas chromatography/mass spectrometry (GC/MS, and GC coupled with high-resolution MS), are provided in the ESI.†

Characterization

¹H NMR and ¹³C NMR spectra were recorded in CDCl₃ using Me₄Si as an internal standard with a Bruker 400 MHz spectrometer. Elemental analysis was performed using a Flash 2000 Elemental Analyzer (EA). UV-vis spectra were recorded using a Shimadzu UV-1601PC spectrophotometer, and the optical band gap was determined from the absorption origin of these spectra. Photoluminescence (PL) spectra were collected using a Jasco FP-6500 fluorescence spectrophotometer. The triplet energy level was measured using a 1 × 10⁻⁵ M solution of the compound at −196 °C. Transient PL measurements were performed using a HAMAMATSU Quantaurus-Tau C11367 instrument. A quartz film composed of 9-(3-(triphenylsilyl)phenyl)-9H-3,9′-bicarbazole (SiCzCz) and 9,9′-(6-(3-(triphenylsilyl)phenyl)-1,3,5-triazine-2,4-diyl)bis(9H-carbazole) (SiTrzCz2) as co-host materials was used, and the decay time of films doped with 20 wt% of each emitter was determined. The PLQYs of the materials doped into the films were measured using a Jasco FP-8000 fluorescence spectrophotometer. The angle-dependent PL (ADPL) was measured using a JooAm angular luminescence spectrometer by doping 20 wt% of each emitter into the co-host material. The electrochemical properties of DOB-1, DOB-2, and DOB-3 were characterized using anhydrous methylene chloride (HPLC grade) as the solvent, 0.1 M tetrabutylammonium perchlorate (TBAClO₄) as the supporting electrolyte, glassy carbon as the working electrode, and Ag/AgCl (0.01 M NaCl) as the reference electrode. Thermogravimetric analysis (TGA) was conducted using a Rigaku Thermo plus EV02 system in a nitrogen atmosphere at a heating rate of 10 °C min⁻¹. Differential scanning calorimetry (DSC) was performed using a Shimadzu DSC-60 calorimeter under nitrogen at a heating rate of 10 °C min⁻¹. Column chromatography was carried out using Merck silica gel (70–230 mesh). The electroluminescence (EL) spectra and Commission Internationale de l’Éclairage (CIE) color coordinates of the TADF OLEDs were obtained using a CS-2000 spectroradiometer, and the current–voltage–luminescence (J–V–L) characteristics were measured using a Keithley 2400 SourceMeter.

Theoretical calculations of TADF materials

The optical geometry of the designed molecules, namely, DOB-1, DOB-2, and DOB-3, was calculated using the density functional theory with the B3LYP/6-31G* basis set in the Schrödinger program.

As shown in Fig. 1, the LUMO of the three TADF emitters extended from the DOBNA moiety to the CN substituent in the acceptor structure, and the LUMOs of the three materials (DOB-1, DOB-2, and DOB-3) were similar (−2.29, −2.23, and −2.24 eV, respectively). Furthermore, the HOMOs of DOB-1, DOB-2, and DOB-3 (−5.54, −5.33, and −5.26 eV) were distributed over the two carbazole donors. Consequently, the HOMO levels for DOB-2 and DOB-3 were higher because the electron-donating characteristics of 3,6-tert-9H-carbazol-9-yl (in DOB-2) and 3,6-diphenyl-9H-carbazol-9-yl (in DOB-3) are superior to that of 9H-carbazole.^30,31

The energies of the singlet excited states of DOB-1, DOB-2, and DOB-3 were 2.87, 2.61, and 2.56 eV, respectively, and those of their triplet excited states were 2.63, 2.52, and 2.49 eV. These energies led to low ΔE_ST values of 0.24, 0.09, and 0.07 eV, respectively, which can be attributed to the efficient separation of the FMOs.

Photophysical properties

The three TADF emitters were pretreated in a 1.0 × 10⁻⁵ M solution, and their UV-vis, room-temperature photoluminescence (RTPL), and low-temperature photoluminescence (LTPL) properties were measured; the corresponding results are shown in Fig. 2 and summarized in Table 1.

---

The UV-vis spectra indicate that the π–π* transition, which is a characteristic of the carbazole donor, occurred at approximately 290 nm in all the emitters, while the n–π* transition, which is attributed to the back-bone structure of the molecules, occurred at 310–350 nm. The CT molar extinction coefficients were 31803 M⁻¹ cm⁻¹ for DOB-1, 21988 M⁻¹ cm⁻¹ for DOB-2, and 35333 M⁻¹ cm⁻¹ for DOB-3, respectively. Therefore, the strength of CT absorption intensity of DOB-3 was larger than the that of the other materials. The RTPL spectra show that DOB-2 and DOB-3 emitted at wavelengths of 478 and 481 nm, respectively, and these two peaks redshifted with respect to that of DOB-1 at 454 nm. All three materials were therefore deemed suitable for application in blue TADF OLED devices. The LTPL spectra revealed that the T₁ values of the three emitters were all approximately 2.8 eV, and the measured ΔE_ST values for DOB-1, DOB-2, and DOB-3 were 0.11, 0.07, and 0.03 eV, respectively, which agree well with the simulation results. These results suggest that an efficient RISC occurs in the TADF materials.

For application in blue TADF OLED devices, DOB-1, DOB-2, and DOB-3 were each doped at 20 wt% into a quartz film using p-type SiCzCz and n-type SiTrzCz2 as co-hosts. The PLQY and time-resolved PL were measured, and the results are presented in Fig. 3 and Table 2. The absolute PLQYs of DOB-1, DOB-2, and DOB-3 were 0.83, 0.92, and 0.95, respectively, indicating that DOB-2 and DOB-3, which exhibit higher quantum efficiencies, are expected to have higher EQEs than that of DOB-1. Moreover, k_RISC is expected to increase, as the delayed components of PLQY increase sequentially for DOB-1, DOB-2, and DOB-3. The calculated values of the oscillator strength (f) for the three emitters were 0.044, 0.059, and 0.065, which align with the trend observed in the PLQY results. The RISC rates of DOB-1, DOB-2, and DOB-3 were calculated to be high, at 2.36, 4.04, and 9.47 × 10⁵ s⁻¹, respectively, indicating that the RISC rate of DOB-3 surpassed those of DOB-1 and DOB-2; this result can be attributed to the relatively small ΔE_ST values. Furthermore, the values of τ_d for DOB-1, DOB-2, and DOB-3 were 18.7, 12.7, and 5.18 μs, respectively, indicating that DOB-3, with its short triplet exciton lifetime, exhibits a high RISC rate, which results in a long lifetime and low efficiency roll-off ratio during the operation of the device.

---

The HOMO–LUMO energy levels, highest occupied natural transition orbitals (HONTOs), and lowest unoccupied natural transition orbitals (LUNTOs) of the three TADF emitters were calculated using the Schrödinger program to analyze the charge-transfer (CT) characteristics, locally excited (LE) characteristics, and harvesting mechanism of the triplet exciton using natural transition orbitals (NTOs) and SOCMEs, as shown Fig. 4.

According to the El-Sayed rule,³⁰ transitions from the singlet to triplet excited states, such as ³CT → ¹CT and ³LE → ¹LE, are forbidden, whereas transitions between other states are allowed, such as ³LE → ¹CT.¹⁶ However, the distributions of the HOMO and LUMO in the singlet excited state show a small orbital overlap in the ¹CT characteristics. In the D–A–D structure, the HOMO and HOMO−1 had similar energy levels and were distributed in the carbazole donor (Fig. S1, ESI†). As a result, S^CT₁ and S^CT₂ are expected to be generated, which can enhance 〈S₁|H^SOC|T_n〉 (n = 1, 2, 3). This enhancement is expected to provide good TADF properties because ICT occurs efficiently in the TADF process, which can increase RISC.¹⁶ The examination of the overlap in the distribution of the HONTO and LUNTO within the NTO distribution revealed that the emitters exhibited CT characteristics in the S₁, T₁, and T₂ states.

For DOB-1, DOB-2, and DOB-3, the calculated values of 〈S₁|H^SOC|T₁〉 were 0.16, 0.19, and 0.24 cm⁻¹, respectively, and those of 〈S₁|H^SOC|T₂〉 were 0.99, 1.17, and 0.99 cm⁻¹. According to the calculated results, the primary SOC mechanism involved up-conversion from T₂ to S₁ for all three materials, as shown in Fig. 5. However, transitions between the same states are permitted beyond a certain value; based on this, the SOCME value of 〈S₁|H^SOC|T₂〉 is the largest among all three materials. Fast spin–vibronic coupling from the T₁ to T₂ state results in interconversion, accelerating RISC from T₂ to S₁, which results in the good TADF characteristics and corresponding RISC values of three emitters.^32–36

Electrochemical and thermal properties

To calculate the HOMO energy levels, the oxidation potential was measured through cyclic voltammetry (CV), as shown in Fig. S2(a) and Table S1 (ESI†), with ferrocene as the standard material. The calculated HOMO energy levels of DOB-1, DOB-2, and DOB-3 were −5.80, −5.66, and −5.48 eV, respectively, which indicate that the HOMO energy level increased with the strength of the donor. The optical band gap (Op.Bg) was determined from the edge in the UV-vis spectra; as a result, the corresponding calculated LUMO energy levels were −2.87, −2.84, and −2.85 eV, respectively. The LUMO energy levels are thought to be similar because of the acceptor core, and these tendencies are similar to those of the previous simulation results.

The thermal characteristics, including stability, of the materials were determined through TGA and DSC. DOB-1, DOB-2, and DOB-3 exhibited high decomposition temperatures (weight loss of 5%, T_d) of 444, 483, and 551 °C, respectively, indicating that these materials could withstand the heat generated during device operation. DOB-2 and DOB-3 exhibited high glass transition temperatures (T_g) of 231 and 240 °C, respectively (the T_g of DOB-1 was not measured). As a result, DOB-3 exhibited the highest thermal stability, suggesting the longest device lifetime. The results are shown in Fig. S2(b) and (c) and Table S1 (ESI†).

Device performance of blue TADF OLEDs

We evaluated the device lifetimes and efficiencies of three TADF emitters. The TADF OLED with a structure of ITO/HAT-CN (10 nm)/BCFN (50 nm)/SiCzCz (5 nm)/SiCzCz:SiTrzCz2:emitters (EML, 35 nm)/mSiTrz (5 nm)/mSiTrz:Liq (5:5, 31 nm)/LiF (1 nm)/Al (100 nm) was fabricated through vacuum deposition. The EML comprised TADF emitters doped into the exciplex host (65:35%) with a doping concentration of 20 wt%. The thickness of each layer and the energy-level diagram of this TADF OLED device are shown in Fig. S5 (ESI†). The performance data of the devices are shown in Fig. 6 and summarized in Table 3.

---

The DOB-2- and DOB-3-based OLEDs exhibited maximum EQE (EQE_Max) values of 23.6% and 28.7%, respectively, which are higher than that of the DOB-1-based device (14.0%). To verify this result, the HTDO ratios of the three materials were analyzed through ADPL spectroscopy, as shown in Fig. 7. A high HTDO ratio in the film state allows effective out-coupling in the device, which can enhance the photon efficiency and EQE.^37–39 The measurements were conducted using films separately doped with 20 wt% of DOB-1, DOB-2, and DOB-3, which showed high HTDO ratios of 0.74, 0.86, and 0.90, respectively, because of the robust planar DOBNA and robust carbazole derivatives, which were used as the acceptor and donors, respectively. To obtain results based on the correlation between the emission dipole orientation and the molecular structure, the transition dipole moments (TDMs) from the singlet excited state to the singlet ground state of the emitter were calculated using the Schrödinger program. The TDM vectors possessed a major y component and minor x and z components, which was attributed to the robust acceptor and donor structures. The vectors (x, y, z) of DOB-1, DOB-2, and DOB-3 were (−0.0148, 1.7863, 1.2168), (0.1882, 1.8844, 1.0105), and (−0.1472, 1.9013, 0.6607), respectively, and a high HTDO ratio was observed because the y component of the main axis was large in DOB-3. Thus, the PLQYs of DOB-2 and DOB-3 were high (>0.92).^40–42 Therefore, the trend in the EQE results is attributed to both the high PLQY, which exceeded 0.92, and the excellent HTDO ratio.

In addition, the EQE values at 1000 cd m⁻² were 9.23%, 19.2%, and 14.6%, and the efficiency roll-off ratios were 34.0%, 15.0%, and 14.2%, with DOB-3 showing the smallest roll-off. The maximum current efficiency (CE_Max) values were 32.5, 63.3, and 72.3 cd A⁻¹, which show the same trend as that of the EQE values. The EL wavelengths of the three materials were measured to be 476, 488, and 496 nm, respectively, which is consistent with the observed photophysical property results.

The lifetimes of the DOB-1, DOB-2, and DOB-3 devices for the luminance to decay to 50% of the initial luminance (LT₅₀) were 303, 763, and 1377 h, respectively. Thus, DOB-3 exhibited a long lifetime, approximately 4.5 times longer than that of DOB-1. The extended lifetime and reduced efficiency roll-off ratio of DOB-3 can be attributed to the short delayed fluorescence lifetime of 5.18 μs and high RISC of 9.47 × 10⁵ s⁻¹. Thus, reductions in the efficiency and lifetime caused by quenching processes such as TTA and TPA were effectively inhibited. In addition, the structural stability can be confirmed by measuring the anion bond dissociation energy (BDE), as shown in Fig. S3 (ESI†). The anion BDE of DOB-1 (2.70 eV) increased to 2.90 and 2.98 eV for DOB-2 and DOB-3, respectively, and the lifetime was increased by the higher structural stability, which resulted from the strengthening of the weakest bond in the molecule. Furthermore, UV stability tests experimentally supported the anion BDE calculations.⁴³ The variation in the PL of the three emitters according to the UV exposure time is shown in Fig. S4 (ESI†), revealing that DOB-2 and DOB3 have better UV stability than DOB-1, indicating improved exciton stability. When designing the material, the introduction of groups with electron-donor characteristics at the weak positions of the carbazole donor, namely the 3 and 6 positions, suppressed TTA and TPA processes and intramolecular quenching, thereby stabilizing the device and improving the lifetimes of DOB-2 and DOB-3 with respect to that of DOB-1. Importantly, the DOB-3 device exhibited excellent performance; thus, its efficiency and EL spectra were measured again after lifetime measurements (1377 h at 2000 cd m⁻²) (Fig. S5, ESI†). After this test, the EQE_max and EQE at 2000 cd m⁻² of the device decreased to 14.3% and 12.3%, respectively. Although its EQE_max decreased by 25% with respect to the initial value, its efficiency roll-off remained satisfactory at 13.9%, and the wavelength did not change.

Conclusions

In this study, three types of blue TADF emitter materials, DOB-1, DOB-2, and DOB-3, were designed and evaluated. These three materials were designed at the molecular level to realize long lifetimes and high efficiencies. A high PLQY, HTDO ratio, and RISC rate were attained by selecting robust and stable DOBNA and a CN substituent for π-conjugation extension as the acceptor. In addition, a carbazole unit substituted with tert-butyl or phenyl groups at the 3 and 6 positions was adopted as the donor. The device evaluation results showed that DOB-3 (with phenyl groups) exhibited a high EQE of 28.7%, owing to a high PLQY of 0.95, strengthened out-coupling owing to a high HTDO ratio of 0.90, and a high RISC rate. In addition, DOB-3 achieved a long lifetime (LT₅₀) of 1377 h at 2000 cd m⁻², which can be attributed to the suppression of TTA and TPA as well as the small ΔE_ST of 0.03 eV, high anion BDE of 2.98 eV, short triplet exciton lifetime (i.e., the delayed fluorescence lifetime) of 5.18 μs, and high k_RISC of 9.47 × 10⁵ s⁻¹.

Author contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Jeong-Yeol Yoo and Seung Wan Kang contributed equally to this work.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the Ministry of Trade, Industry, and Energy of the Republic of Korea (RS-2024-00419747) and (RS-2024-00439679) and also the Technology Innovation Program (20022488) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea).

References

1. C. Adachi, M. A. Baldo, M. E. Thompson and S. R. Forrest, J. Appl. Phys., 2001, 90(10), 5048–5051 CrossRef CAS .
2. Q. Zhang, B. Li, S. Huang, H. Nomura, H. Tanaka and C. Adachi, Nat. Photonics, 2014, 8(4), 326–332 CrossRef CAS .
3. Y. Tao, K. Yuan, T. Chen, P. Xu, H. Li, R. Chen, C. Zheng, L. Zhang and W. Huang, Adv. Mater., 2014, 26(47), 7931–7958 CrossRef CAS PubMed .
4. C. Xiang, X. Fu, W. Wei, R. Liu, Y. Zhang, V. Balema, B. Nelson and F. So, Adv. Funct. Mater., 2016, 26(9), 1463–1469 CrossRef CAS .
5. S. Reineke, K. Walzer and K. Leo, Phys. Rev. B: Condens. Matter Mater. Phys., 2007, 75(12), 125328 CrossRef .
6. T. H. Ha, K. W. Kim, Y. J. Choi, S. W. Kang, J. Y. Yoo and C. W. Lee, J. Lumin., 2023, 258, 119787 CrossRef CAS .
7. X. Song, Y. Nie, C. Jiang, B. Liang, J. Liang, X. Zhuang, H. Bi and Y. Wang, Org. Electron., 2024, 125, 106973 CrossRef CAS .
8. Q. Wang, I. W. H. Oswald, M. R. W. H. Perez, H. Jia, B. E. Gnade and M. A. Omary, Adv. Funct. Mater., 2013, 23(43), 5420–5428 CrossRef CAS .
9. D. Wang, C. Cheng, T. Tsuboi and Q. Zhang, CCS Chem., 2020, 2(4), 1278–1296 CrossRef CAS .
10. H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, Nature, 2012, 492(7428), 234–238 CrossRef CAS PubMed .
11. K. Shizu, H. Tanaka, M. Uejima, T. Sato, K. Tanaka, H. Kaji and C. Adachi, J. Phys. Chem. C, 2015, 119(3), 1291–1297 CrossRef CAS .
12. T. Zhang, Y. Xiao, H. Wang, S. Kong and R. Huang, Angew. Chem., Int. Ed., 2023, 62(39), e202301896 CrossRef CAS PubMed .
13. T.-T. Bui, F. Goubard, M. Ibrahim-Ouali, D. Gigmes and F. Dumur, Beilstein J. Org. Chem., 2018, 14, 282–308 CrossRef CAS PubMed .
14. P. Rajamalli, N. Senthilkumar, P. Gandeepan, C.-C. Ren-Wu, H.-W. Lin and C.-H. Cheng, ACS Appl. Mater. Interfaces, 2016, 8(40), 27026–27034 CrossRef CAS PubMed .
15. J.-M. Teng, Y.-F. J.-M. Wang and C.-F. Chen, J. Mater. Chem. C, 2020, 8(33), 11340–11353 RSC .
16. H. Lee, R. Braveenth, S. Muruganantham, C. Y. Jeon, H. S. Lee and J. H. Kwon, Nat. Commun., 2023, 14(1), 419 CrossRef CAS PubMed .
17. J. Li, Y. Xia, G. Li, M. Chen, J. Zhou, W. Yan, B. Zhao, K. Guo and H. Wang, Chem. Eng. J., 2023, 470, 143966 CrossRef CAS .
18. X. Cai, D. Chen, K. Gao, L. Gan, Q. Yin, Z. Qiao, Z. Chen, X. Jiang and S. J. Su, Adv. Funct. Mater., 2018, 28(7), 1704927 CrossRef .
19. I. S. Park, H. Min, J. U. Kim and T. Yasuda, Adv. Opt. Mater., 2021, 9(24), 2101282 CrossRef CAS .
20. D. Hall, S. M. Suresh, P. L. Dos Santos, E. Duda, S. Bagnich, A. Pershin, P. Rajamalli, D. B. Cordes, A. M. Z. Slawin, D. M. Z. Beljonne, A. Köhler, I. D. W. Samuel, Y. D. W. Olivier and E. Zysman-Colman, Adv. Opt. Mater., 2020, 8(2), 1901627 CrossRef CAS .
21. H. Hirai, K. Nakajima, S. Nakatsuka, K. Shiren, J. Ni, S. Nomura, T. Ikuta and T. Hatakeyama, Angew. Chem., Int. Ed., 2015, 54(46), 13581–13585 CrossRef CAS PubMed .
22. K. R. Naveen, R. K. Konidena and P. Keerthika, Chem. Rec., 2023, 23(11), e202300208 CrossRef CAS PubMed .
23. H. Lee, D. Karthik, R. Lampande, J. H. Ryu and J. H. Kwon, Front. Chem., 2020, 8, 373 CrossRef CAS PubMed .
24. M. Hirai, N. Tanaka, M. Sakai and S. Yamaguchi, Chem. Rev., 2019, 119(14), 8291–8331 CrossRef CAS PubMed .
25. A. Wakamiya and S. Yamaguchi, Bull. Chem. Soc. Jpn., 2015, 88(10), 1357–1377 CrossRef CAS .
26. S. S. Kothavale and J. Y. Lee, Adv. Opt. Mater., 2020, 8(22), 2000922 CrossRef CAS .
27. Y. H. Lee, W. Lee, T. Lee, D. Lee, J. Jung, S. Yoo and M. H. Lee, ACS Appl. Mater. Interfaces, 2021, 13(38), 45778–45788 CrossRef CAS PubMed .
28. D. Song, Y. Yu, L. Yue, D. Zhong, Y. Zhang, X. Yang, Y. Sun, G. Zhou and Z. Wu, J. Mater. Chem. C, 2019, 7, 11953–11963 RSC .
29. X. Chen, S. Liu, D. Zhong, Z. Feng, X. Yang, B. Su, Y. Sun, G. Zhou, B. Jiao and Z. Wu, Mater. Chem. Front., 2023, 7, 1841–1854 RSC .
30. Y. Im, M. Kim, Y. J. Cho, J.-A. Seo, K. S. Yook and J. Y. Lee, Chem. Mater., 2017, 29(5), 1946–1963 CrossRef CAS .
31. N. Li, F. Ni, X. Lv, Z. Huang, X. Cao and C. Yang, Adv. Opt. Mater., 2022, 10(1), 2101343 CrossRef CAS .
32. C. Yin, D. Zhang and L. Duan, Appl. Phys. Lett., 2020, 116(12), 120503 CrossRef CAS .
33. T. Wang, A. K. Gupta, D. B. Cordes, A. M. Z. Slawin and E. M. Z. Zysman-Colman, Adv. Opt. Mater., 2023, 11(10), 2300114 CrossRef CAS .
34. K. Kumada, H. Sasabe, M. Matsuya, N. Yoshida, K. Hoshi, T. Nakamura, H. Nemma and J. Kido, J. Mater. Chem. C, 2023, 11(40), 13782–13787 RSC .
35. I. Kim, K. H. Cho, S. O. Jeon, W.-J. Son, D. Kim, Y. M. Rhee, I. Jang, H. Choi and D. S. Kim, JACS Au, 2021, 1(7), 987–997 CrossRef CAS PubMed .
36. Z. Zhao, S. Yan and Z. Ren, Acc. Chem. Res., 2023, 56(14), 1942–1952 CrossRef CAS PubMed .
37. F. Tenopala-Carmona, O. S. Lee, E. Crovini, A. M. Neferu, C. Murawski, Y. Olivier, E. Zysman-Colman and M. C. Gather, Adv. Mater., 2021, 33(37), e2100677 CrossRef PubMed .
38. G. Zhao, D. Liu, P. Wang, X. Huang, H. Chen, Y. Zhang, D. Zhang, W. Jiang, Y. Sun and L. Duan, Angew. Chem., Int. Ed., 2022, 61(45), e202212861 CrossRef CAS PubMed .
39. S. Y. Byeon, J. Kim, D. R. Lee, S. H. Han, S. R. Forrest and J. Y. Lee, Adv. Opt. Mater., 2018, 6(15), 1701340 CrossRef .
40. Y. Chen, D. Zhang, Y. Zhang, X. Zeng, T. Huang, Z. Liu, G. Li and L. Duan, Adv. Mater., 2021, 33(44), e2103293 CrossRef PubMed .
41. T. Hua, Y.-C. Liu, C.-W. Huang, N. Li, C. Zhou, Z. Huang, X. Cao, C.-C. Wu and C. Yang, Chem. Eng. J., 2022, 433, 133598 CrossRef CAS .
42. C. Zhou, C. Cao, D. Yang, X. Cao, H. Liu, D. Ma, C.-S. Lee and C. Yang, Mater. Chem. Front., 2021, 5(7), 3209–3215 RSC .
43. H. J. Lee, H. L. Lee, S. H. Han and J. Y. Lee, Chem. Eng. J., 2022, 427, 130988 CrossRef CAS .

---

Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4tc03016h

‡ These authors contributed equally.

This journal is © The Royal Society of Chemistry 2024