View PDF Version
 
DOI: 10.1039/D4TC02592J (Paper) J. Mater. Chem. C, 2024, Advance Article

Modification of thermally activated delayed fluorescence emitters comprising fluorinated acridan–quinazoline and spiroacridan–quinazoline moieties for efficient green OLEDs†

Fu-En Szua, Shao-An Chenb, Yin-Yin Yua, Jiun-Haw Lee*b, Tien-Lung Chiu*c and Man-kit Leung*ad
aDepartment of Chemistry, National Taiwan University, Taipei 10617, Taiwan. E-mail: mkleung@ntu.edu.tw
bGraduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan. E-mail: jiunhawlee@ntu.edu.tw
cDepartment of Electrical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan. E-mail: tlchiu@saturn.yzu.edu.tw
dAdvanced Research Center for Green Materials Science and Technology, National Taiwan University No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan, Republic of China

Received 20th June 2024 , Accepted 15th August 2024

First published on 16th August 2024

Abstract

We synthesize two new TADF emitters, 4Ac5FQN and 4SpAc5FQN, using acridan or spiroacridan as the donor and 5-fluoroquinazoline as the acceptor, with the introduction of F atoms into the molecules to enhance the TADF effect. These emitters exhibit emissions at 538 nm and 536 nm in electroluminescent devices, falling within the pure green light range. Both compounds exhibit small energy differences (ΔEST) of 0.02 eV and 0.07 eV between their singlet and triplet states, confirming their TADF characteristics. Notably, there is a long decay of up to 10 ms for these emitters in OLEDs. OLEDs utilizing 4SpAc5FQN achieve outstanding performance with the maximum external quantum efficiency (ηEQE) of 22.1%.

Introduction

Materials exhibiting thermally activated delayed fluorescence (TADF) are emerging as effective metal-free options for organic light-emitting compounds in display and lighting technologies. TADF emitters are capable of converting their triplet (T1) excitons back to the singlet S1 state through reverse intersystem crossing (rISC) for fluorescence emission, thereby achieving maximal exciton utilization efficiency and internal quantum efficiency (IQE) in organic light-emitting diodes (OLEDs).1–6 Typically, TADF molecules are characterized by their structure, which includes strong donor and acceptor groups connected via orthogonally arranged aromatic rings.6–8 This structural arrangement results in a minimal singlet–triplet energy gap (ΔEST), enhancing the rISC rate and improving the OLED performance.4,7,9–11 Additionally, the arrangement of the aromatic units in an orthogonal fashion provides a sterically shielding effect, reducing π-stacking among molecules and minimizing intermolecular quenching of the excitons. Quinazoline, a planar heterocyclic molecule with benzene and pyrimidine rings, is notable for TADF-OLED applications.3,11–14 Zhang reported four new TADF emitters shown in Fig. 1, 4HQ-PXZ, 4PQ-PXZ, 2HQ-PXZ, and 2PQ-PXZ.12 These four materials show small ΔEST between 0.09 and 0.22 eV. 2PQ-PXZ and 4PQ-PXZ show green and yellow-green emissions. Superior OLED performance with the maximum external quantum efficiencies (EQEs) of 20.5% and 17.6% and CEs of 65.6 cd A−1 and 55.7 cd A−1 was reported.
image file: d4tc02592j-f1.tif
Fig. 1 TADF emitters reported by Zhang.12

The fluorine substituent has been known to act as an auxiliary acceptor to minimize the single (S1)–triplet (T1) energy gaps and could promote the rISC process.15–20

Recently, we developed a simple one-pot synthetic method for fluoro-substituted quinazoline derivatives.21 We put our efforts into further developing new D–A type quinazoline-based emitters and evaluating their electroluminescence (EL) performance. We adopt quinazoline (QN) as a basic framework and incorporate acridan and spiroacridan functionalities onto the QN skeleton at the 2- and 4- positions. Consequently, two novel TADF materials of 4Ac5FQN and 4SpAc5FQN are derived, as shown in Fig. 2. Both compounds have a similar ΔEST (<0.2 eV), which is satisfactory for their use as TADF materials with similar quantum yields of around 45%. OLEDs utilizing 4Ac5FQN and 4SpAc5FQN show green EL emissions peaked at 538 and 536 nm, whose optimized efficiency performance reaches the highest ηEQE of 20.2% and 22.1%, respectively.


image file: d4tc02592j-f2.tif
Fig. 2 Molecular structures of 4Ac5FQN and 4SpAc5FQN.

Results and discussion

Synthesis of 4Ac5FQN and 4SpAc5FQN

General procedure.
4Ac5FQN. A two-neck flask under an argon atmosphere was charged with Pd2(dba)3 (229 mg, 0.1 mmol), 5-fluoro-2,4-bis(4-bromophenyl)quinazoline21 (458 mg, 1.0 mmol), sodium tert-butoxide (721 mg, 3.0 mmol), XPhos (238 mg, 0.2 mmol) and 9,9-dimethyl-9,10-dihydroacridine (2.2 mmol). Dry and de-aerated toluene (10 mL) was added. The mixture was refluxed for 15 h. After cooling, the reaction mixture was diluted with dichloromethane (DCM) filtered through Celite and dried over anhydrous MgSO4. The solvent was evaporated under vacuum, and the crude product was purified by liquid column chromatography on silica gel (DCM/hexane = 1/3).
4pAc5FQN. A two-neck flask under an argon atmosphere was charged with Pd2(dba)3 (229 mg, 0.1 mmol), 5-fluoro-2,4-bis(4-bromophenyl)quinazoline (458 mg, 1.0 mmol), sodium tert-butoxide (721 mg, 3.0 mmol), XPhos (238 mg, 0.2 mmol) and 10H-spiro[acridine-9,9′-fluorene] (2.2 mmol). Dry and de-aerated toluene (10 mL) was added. The mixture was refluxed for 15 h. After cooling, the reaction mixture was diluted with DCM, filtered through Celite, and dried over anhydrous MgSO4. The solvent was evaporated under vacuum and the crude product was purified by liquid column chromatography on silica gel (DCM/hexane = 1/3).

The synthetic routes for 4Ac5FQN and 4SpAc5FQN are depicted in Scheme 1 and Fig. S1–S16 (ESI†). Both compounds were synthesized from 1,3-difluorobenzene using LDA and anhydrous 4-bromobenzonitrile through [2+2+2] cascade annulation.21 Subsequently, 4Br5FQN was subjected to the Buchwald–Hartwig amination with 2 equivalents of 9,9-dimethyl-9,10-dihydroacridine (Ac) and 10H-spiro[acridine-9,9′-fluorene] (SpAc), resulting in the formation of 4Ac5FQN and 4SpAc5FQN in high yields. Both compounds were further purified through sublimation under reduced pressure (<1 × 10−5 torr), and their structures and molecular packing in their crystal lattices were evaluated by using 1H NMR spectroscopy, 13C NMR spectroscopy, 19F NMR spectroscopy, high-resolution mass spectrometry (HRMS), and single-crystal X-ray diffraction (XRD). The synthetic methodology and corresponding NMR spectra of 4Ac5FQN and 4SpAc5FQN are presented in Fig. S1–S6 (ESI†).


image file: d4tc02592j-s1.tif
Scheme 1 Synthetic routes of 4Ac5FQN and 4SpAc5FQN.

Crystallographic analysis

X-ray crystallographic analysis of 4Ac5FQN suggests that the acridan and quinazoline units are more or less perpendicular to the benzene ring (Fig. 3). The dihedral angle for 4Ac5FQN between the benzene ring and acridan moiety is 86.91° (87.53°). On the other hand, the dihedral angle between the benzene and the quinazoline is 9.35° (37.13°), and for 4SpAC5FQN the dihedral angle between the benzene ring and spiroacridan moiety is 73.82° (102.13°). On the other hand, the dihedral angle between the benzene and the quinazoline is 17.22° (98.22°).
image file: d4tc02592j-f3.tif
Fig. 3 Molecular structures of (a) 4Ac5FQN and (b) 4SpAc5FQN with thermal ellipsoids drawn at a 50% probability level.

Since the dihedral angle between the benzene ring and quinazoline is not large, the LUMO will mainly fall on quinazoline and the benzene ring, and the HOMO will fall on the acridan moiety. Because the dihedral angle between the donor and acceptor is almost vertical, we expect that 4Ac5FQN and 4SpAc5FQN should have a similar ΔEST.

Thermal properties

The thermal properties of 4Ac5FQN and 4SpAc5FQN were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and the results and the data are provided in Fig. S7 and S8 (ESI†), respectively. 4Ac5FQN and 4SpAc5FQN both exhibit a high thermal decomposition temperature (Td, corresponding to 5% weight loss) of 495 and 467 °C, respectively.

In the DSC analysis of 4SpAc5FQN, the glass transition temperature (Tg) or melting temperature (Tm) could not be observed below 350 °C, indicating the high thermal stability of the amorphous phase. For 4Ac5FQN, high Tg, Tc and Tm values of 140, 181, and 271 °C were recorded, respectively. In short, 4Ac5FQN and 4SpAc5FQN are structurally robust enough for OLED applications.

Electrochemical properties

The energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of 4Ac5FQN and 4SpAc5FQN were evaluated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and are summarized in Table 1 and Fig. S9 (ESI†). The oxidation sweeps were measured in DCM, and the reductive sweeps were performed in N,N-dimethylformamide. The HOMO and LUMO levels were calculated using the DPV value of the oxidation and the reduction.22,23 The values of EoxDPV and EreDPV for 4Ac5FQN and 4SpAc5FQN are 0.48/−1.74 and 0.53/−1.84 V, respectively, when using ferrocene as an internal standard. Therefore, the HOMO/LUMO levels of 5.38/3.20 eV and 5.44/3.11 eV for 4Ac5FQN and 4SpAc5FQN are estimated. The higher HOMO with a lower LUMO level of 4Ac5FQN implies that 4Ac5FQN should be a better electron donor and acceptor than 4SpAc5FQN.
Table 1 Photophysical properties of 4Ac5FQN and 4SpAc5FQN
Material Absorption solutiona [nm]/film Eg[thin space (1/6-em)]b solution [eV]/film Emission solutiona [nm]/film S1e [eV] T1e [eV] ΔEST [eV] Φf solution [%]/film Energy levelg [eV] HOMO/LUMO
λabsonset λFLmax[thin space (1/6-em)]a λFLonset[thin space (1/6-em)]c λFLonsed[thin space (1/6-em)]d
a Measured in a solution of THF (1 × 10−5 M).b Estimation of the energy gap using the equation of 1240.8/λabsonset.c Measured in THF with the concentration of 1 × 10−5 M at 298 K.d Measured in 2Me-THF with the concentration of 1 × 10−5 M at 77 K.e Estimation of singlet and triplet state energies using equations of 1240.8/λFLonset and 1240.8/λLTPHonsed.f 4CzIPN was used as a reference in cyclohexane.g Value in film: HOMO is measured by AC-II and LUMO = HOMO−Eg.h Doped film of 4Ac5FQN or 4SpAc5FQN in o-DiCbzBz.
4Ac5FQN 445/483 2.8/2.6 541/535, 514h 486 490 2.55 2.53 0.02 37/51 5.7/3.1
4SpAc5FQN 443/501 2.8/2.5 523/524, 502h 477 490 2.60 2.53 0.07 44/56 5.8/3.3

Photophysical properties

UV-vis absorption and photoluminescence spectra of solutions of 4Ac5FQN and 4SpAc5FQN at 1 × 10−5 M were recorded in tetrahydrofuran (THF) at ambient temperature and in 2-methyltetrahydrofuran (2-MeTHF) at 77 K. The solution in 2-MeTHF forms homogeneous organic glass at low temperatures, preventing precipitation of the sample molecules from the solvent. In addition, photoluminescence (PL) spectra of thin films consisting of 5% 4Ac5FQN and 15% 4SpAc5FQN doped in 9,9′-(2-(1-phenyl-1H-benzo[d]imidazol-2-yl)-1,3- phenylene)bis(9H-carbazole) (o-DiCbzBz) were also collected for understanding the photophysical characteristics of the OLEDs. The spectral data are depicted in Fig. 4 and summarized in Table 1.
image file: d4tc02592j-f4.tif
Fig. 4 UV-vis and PL spectra of (a) 4Ac5FQN and (b) 4SpAc5FQN in solution and (c) thin films of 4Ac5FQN and 4SpAc5FQN doped in an o-DiCbzBz matrix, together with the PL spectrum of the o-DiCbzBz thin film.
UV-vis absorption behavior. As depicted in Fig. 4a and b, 4Ac5FQN and 4SpAc5FQN show similar UV absorption profiles, with pronounced absorption peaks at 273 nm and 276 nm, respectively. These peaks are attributed to the π–π* transitions within the conjugated aromatic moieties. The weaker absorption spanning the 350–450 nm range is assigned to the intramolecular charge transfer (ICT) transitions, primarily from the electron-rich acridan or spiroacridan to the electron-deficient quinazoline unit. The absorption onsets for 4Ac5FQN and 4SpAc5FQN in solution, as deduced from the crossover with the fluorescence spectra at 77 K, are at 445 nm and 443 nm, respectively, corresponding to an optical energy gap (Eg) of 2.8 eV for both according to the Born–Oppenheimer approximation and Frank–Condon principle.
Fluorescence and phosphorescence. 4Ac5FQN and 4SpAc5FQN fluoresce in the sky-blue region at 77 K with the λmax peaked at 474 nm and 464 nm. However, perhaps due to solvent relaxation or structural reorganization in the excited states at room temperature, the fluorescence (FL) λmax red-shifts significantly to 541 nm and 523 nm, respectively, resulting in green luminescence for both compounds. The fluorescence onset wavelengths of 486 nm (2.55 eV) and 477 nm (2.60 ev) are then estimated. The triplet state (T1) energies of 4Ac5FQN and 4SpAc5FQN, derived from the onset of their low-temperature phosphorescence (LTPh) spectra, are both found to be 2.53 eV. The energy splitting between their S1 and T1 states (ΔEST) is predicted to be below 0.2 eV, which is small enough for TADF. This suggests their potential for use as TADF emitters, with efficient triplet exciton harvesting through reverse intersystem crossing (rISC) for TADF emissions.

The solid-state-bathochromic-shift phenomena are consistent with those in solution. In pristine solid thin films, their onsets again red-shift to 483 nm (2.57 eV) and 501 nm (2.48 eV) and peaked at 535 nm and 524 nm, respectively, as illustrated in Fig. S10 (ESI†) and detailed in Table 1. Since solvent relaxation does not exist in the solid state, we tentatively attribute the red-shift phenomena to the intermolecular π–π-stacking effects as well as the structural and conformational reorganization in the lattices. Similar red-shift phenomena are also observed in a doped film of 4Ac5FQN or 4SpAc5FQN in o-DiCbzBz with an emission peak at 514 and 502 nm, respectively, as illustrated in Fig. 4c.

The PLQY of 4SpAc5FQN is higher than that of 4Ac5FQN either in solution or in the film state. Based on the literature, the donor (D) and acceptor (A) units should possess high structural rigidity to ensure high photoluminescence quantum efficiency (PLQY).24 Spiroacridan exhibits a more rigid structure compared to acridan, which increases the rigidity of the molecular structure. This enhanced rigidity may reduce non-radiative decay pathways, thereby improving PLQY. Moreover, due to the larger steric hindrance of SPAC, intramolecular rotations are effectively suppressed, further reducing non-radiative decay.

Density functional theory (DFT) calculations

To substantiate our approach to utilize 4Ac5FQN and 4SpAc5FQN in TADF applications, we have explored the interplay between their donor and acceptor components by density functional theory (DFT) calculations, using DFT/B3LYP/6-31+G(d) methodology at their X-ray geometry. The frontier molecular orbitals HOMO−1, HOMO, LUMO, and LUMO+1, and their energy levels are summarized in Table 2.
Table 2 DFT/B3LYP/6-31+G(d) orbitals and the corresponding orbital energies (in eV) of 4Ac5FQN and 4SpAc5FQN at their respective X-ray structures
Species HOMO−1 HOMO LUMO LUMO+1
4Ac5FQN image file: d4tc02592j-u1.tif image file: d4tc02592j-u2.tif image file: d4tc02592j-u3.tif image file: d4tc02592j-u4.tif
4SpAc5FQN image file: d4tc02592j-u5.tif image file: d4tc02592j-u6.tif image file: d4tc02592j-u7.tif image file: d4tc02592j-u8.tif

Basically, our calculations reveal that 4Ac5FQN and 4SpAc5FQN can be divided into donor and acceptor regions: (1) the electron-donating acridan components and (2) the electron-accepting 5-fluoro-2,4-diphenylquinazoline central core. While the HOMO and HOMO−1 are mainly contributed by the acridan fragments, the LUMO and LUMO+1 are contributed by the 5-fluoro-2,4-diphenylquinazoline core. Even though both materials have a small HOMO and LUMO overlap, they can still interact through the phenylene bridge. This is consistent with the photophysical TADF properties with a reasonable photoluminescence quantum yield. It is noteworthy to mention that the 5-fluoro substituent contributes to the LUMO of both 4Ac5FQN and 4SpAc5FQN. The fluorine nuclear spin may participate in the rISC process.

Device performances of OLEDs

Fig. 5 shows the device architecture of the OLED devices with 4Ac5FQN and 4SpAc5FQN as the emitters, as well as the corresponding energy levels of materials (in units of eV) and molecular structures. In these devices, indium tin oxide (ITO) and aluminum were used as the anode and cathode materials. LiF was used as the electron injection layer (EIL). 1,1-Bis[(di-4- tolylamino)phenyl]cyclohexane (TAPC), N,N-dicarbazolyl-3,5-benzene (mCP), and diphenylbis[4-(pyridin-3-yl)phenyl]silane (DPPS) were used as hole-transporting layer (HTL), electron blocking layer (EBL), and electron transporting layer (ETL) materials, respectively. 4Ac5FQN and 4SpAc5FQN were doped in the host material, 9,9′-(2-(1-phenyl-1H-benzo[d]imidazol-2-yl)-1,3-phenylene)bis(9H-carbazole) (o-DiCbzBz), to form the emitting layer.
image file: d4tc02592j-f5.tif
Fig. 5 Device architecture and the corresponding energy levels of the OLEDs and molecular structures of organic materials.

Fig. 6 and Table 3 show the electrical and optical performances of OLEDs based on 4Ac5FQN and 4SpAc5FQN emitters with optimized structures. Thicknesses of organic thin films and dopant concentration in the emitting layer (EML) were varied to achieve the highest EQE. The detailed optimization procedures are illustrated in Fig. S11–S14 (ESI†) and summarized in Tables S1–S4 (ESI†). After optimization, the layer thicknesses of 4Ac5FQN- and 4SpAc5FQN-based OLEDs are: (HTL/EBL/EML/ETL) = (50 nm/10 nm/30 nm/60 nm) and (50 nm/10 nm/30 nm/55 nm), respectively. The dopant concentration in a volume ratio of 4Ac5FQN and 4SpAc5FQN in the EML was 5% and 15%, respectively. As shown in Fig. 6(a), the driving voltage of the 4SpAc5FQN-based OLED is 7.6 V at 10 mA cm−2, which is lower than that of the 4Ac5FQN one (9.0 V) due to a thinner ETL (55 nm vs. 60 nm) and a higher dopant concentration (15% vs. 5%), which formed a conducive channel. Fig. 6(b) shows the current efficiency (in terms of cd A−1), power efficiency (in terms of lm W−1), and EQE versus the current density of these two OLEDs. Maximum efficiencies of 82.5 cd A−1, 74.2 lm W−1, and 22.1% for the 4SpAc5FQN-based OLED were achieved, respectively, which were all superior to the 4Ac5FQN-based device with 71.9 cd A−1, 64.7 lm W−1, and 20.2%, respectively. Additionally, these devices still demonstrated reasonable efficiencies at a high luminance of 1000 cd m−2, with ηEQE values of 4.1% and 4.9% for 4Ac5FQN and 4SpAc5FQN devices, respectively. The efficiency drop is mainly attributed to TTA (triplet–triplet annihilation), TPA (triplet–polaron annihilation), and/or the loss of carrier balance in OLEDs at high current density.25 Another possible factor can be observed from the TrEL graphs (Fig. 7), showing their relatively long triplet lifetimes, which are reflected in their significantly long luminescence decay times. This leads to accumulation of excessive triplet excitons at higher applied voltages, causing issues associated with triplet–triplet quenching and subsequent efficiency reduction. Fig. 6(c) shows the electroluminescence spectra of these two OLEDs, which were almost the same, although the 4SpAc5FQN-based device exhibited a shorter spectral absorption wavelength, 536 nm, compared to the 4Ac5FQN OLED (538 nm).


image file: d4tc02592j-f6.tif
Fig. 6 (a) J–V and L–V characteristics, (b) efficiencies vs. current density, and (c) EL spectra of OLEDs.
Table 3 Summary of OLED key performances
Device Voltagea (V) Luminanceb (cd m−2) CEc (cd A−1) PEc (lm W−1) EQEc (%) CIEd (x, y) lELd (nm)
a Voltage at J = 10 mA cm−2 and 1 cd cm−2.b Luminance at 10 V.c CE, PE, and EQE measured at maximum, 100 cd m−2, and 1000 cd m−2.d Measured at 5 V.
4Ac5FQN 9.0/3.3 1666 71.9/40.5/14.5 64.7/29.3/7.1 20.2/11.3/4.1 (0.35, 0.58) 538
4SpAc5FQN 7.6/3.2 2570 82.5/47.7/17.6 74.2/33.5/8.0 22.1/12.8/4.9 (0.35, 0.58) 536


image file: d4tc02592j-f7.tif
Fig. 7 TrEL of 4Ac5FQN- and 4SpAc5FQN-based OLEDs.

Although delayed photoluminescence is unsure in the transient photoluminescence (TrPL) measurements (Fig. S16, ESI†), delayed electroluminescence can be clearly recorded in the transient electroluminescence (TrEL) study. Fig. 7 shows the decay dynamics of TrEL measurement of two OLEDs, which were turned off at t = 0. There was a long decay of up to 10 ms, which demonstrated clear TADF characteristics. For an OLED device, EQE (ηEQE) can be described as:

 
ηEQE = ηIQE × ηLE (1)
 
ηIQE = χ × γ × Φ (2)
where ηIQE, ηLE, χ, γ, and Φ are the internal quantum efficiency (IQE), light extraction efficiency, exciton utilization ratio, charge recombination efficiency, and photoluminescence quantum efficiency (PLQY), respectively. As shown in Tables 1 and 3 and Fig. S15 (ESI†), PLQYs of thin films with 4Ac5FQN and 4SpAc5FQN emitters doped in the o-DiCbzBz matrix are 51% and 56%, while the maximum EQE values are 20.2% and 22.1%, respectively. Hence, the products of ηLE, χ, and γ are found to be 39.4% and 39.5%, respectively. To our best knowledge, the highest recorded light extraction efficiency of the OLED ever reported is 44%.26 Hence, we can conclude that light extraction efficiency, the exciton utilization ratio, and charge recombination efficiency are reasonably high. From the TrEL measurements shown in Fig. 7, although the rISC process is very slow, the nonradiative rate is even slower, which resulted in a high exciton utilization ratio.

Conclusions

In summary, we successfully synthesized two new quinazoline-based TADF emitters with introduced F atoms on them, 4Ac5FQN and 4SpAc5FQN. They exhibit pronounced TADF behavior in transient electroluminescence (TrEL) measurements. As a result, OLEDs incorporating 4Ac5FQN and 4SpAc5FQN achieve maximum external quantum efficiencies (ηEQE) of 20.2% and 22.1%, respectively, with emission wavelengths of 538 nm and 536 nm, falling within the pure green light range. Overall, the performance of devices fabricated using 4SpAc5FQN surpasses that of those fabricated using 4Ac5FQN. The comparison of the effects of fluorine atoms at different positions on the quinazoline framework will be the focus of our next study.

Author contributions

Mr Fu-En Szu and Ms Yin-Yin Yu were responsible for synthesizing the materials and analyzing their properties. Mr Shao-An Chen conducted the device fabrication and measurements. Mr Fu-En Szu collaborated on the result analysis and manuscript preparation. Prof. Man-kit Leung, Prof. Jiun-Haw Lee and Prof. Tien-Lung Chiu instructed the device design and measurement, and Prof. Man-kit Leung and Prof. Jiun-Haw Lee also oversaw the paper writing and submission. All authors contributed to the discussion of the results of the manuscript.

Data availability

The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Science and Technology Council (NSTC), Taiwan, under grant numbers 113-2622-E-155 -002, 112-2113-M-002-001, 112-2221-E-002-216-MY3, 112-2221-E-155-028-MY3, 111-2113-M-002-023, 111-2221-E-155-013, 111-2923-E-155-002-MY3, and 110-2222-E-002-003-MY3, and “Advanced Research Center for Green Materials Science and Technology” from The Featured Area Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education, Taiwan: MOE 113L9006.

Notes and references

  1. H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, Nature, 2012, 492, 234–238 CrossRef CAS PubMed .
  2. Z. Yang, Z. Mao, Z. Xie, Y. Zhang, S. Liu, J. Zhao, J. Xu, Z. Chi and M. P. Aldred, Chem. Soc. Rev., 2017, 46, 915–1016 RSC .
  3. P. Li, Y. Xiang, S. Gong, W.-K. Lee, Y.-H. Huang, C.-Y. Wang, C. Yang and C.-C. Wu, J. Mater. Chem. C, 2021, 9, 12633–12641 RSC .
  4. X.-K. Chen, D. Kim and J.-L. Brédas, Acc. Chem. Res., 2018, y, 2215–2224 CrossRef PubMed .
  5. T. Zhang, Y. Xiao, H. Wang, S. Kong, R. Huang, V. Ka-Man Au, T. Yu and W. Huang, Angew. Chem., 2023, 135, e202301896 CrossRef .
  6. K. R. Naveen, P. Palanisamy, M. Y. Chae and J. H. Kwon, Chem. Commun., 2023, 59, 3685–3702 RSC .
  7. H. Lim, H. J. Cheon, S.-J. Woo, S.-K. Kwon, Y.-H. Kim and J.-J. Kim, Adv. Mater., 2020, 32, 2004083 CrossRef CAS PubMed .
  8. M. Liu, R. Komatsu, X. Cai, K. Hotta, S. Sato, K. Liu, D. Chen, Y. Kato, H. Sasabe, S. Ohisa, Y. Suzuri, D. Yokoyama, S.-J. Su and J. Kido, Chem. Mater., 2017, 29, 8630–8636 CrossRef CAS .
  9. B. S. Kim and J. Y. Lee, Adv. Funct. Mater., 2014, 24, 3970–3977 CrossRef CAS .
  10. Y. Im, M. Kim, Y. J. Cho, J.-A. Seo, K. S. Yook and J. Y. Lee, Chem. Mater., 2017, 29, 1946–1963 CrossRef CAS .
  11. U. Shakeel and J. Singh, Org. Electron., 2018, 59, 121–124 CrossRef CAS .
  12. B. Li, Z. Wang, S.-J. Su, F. Guo, Y. Cao and Y. Zhang, Adv. Opt. Mater., 2019, 7, 1801496 CrossRef .
  13. A. E. Kopotilova, M. I. Valieva, E. S. Starnovskaya, T. N. Moshkina, E. V. Nosova, O. S. Taniya, A. A. Kalinichev, D. S. Kopchuk, P. A. Slepukhin, V. S. Gaviko, G. A. Kim and V. N. Charushin, J. Photochem. Photobiol. A, 2024, 448, 115350 CrossRef CAS .
  14. T. N. Moshkina, A. E. Kopotilova, M. A. Ivan’kina, E. S. Starnovskaya, D. A. Gazizov, E. V. Nosova, D. S. Kopchuk, O. S. El’tsov, P. A. Slepukhin and V. N. Charushin, Molecules, 2024, 29, 2497 CrossRef CAS PubMed .
  15. J. A. Asiri, W. M. I. Hasan, A. Jedidi, S. A. Elroby, S. G. Aziz and O. I. Osman, Molecules, 2023, 28, 6952 CrossRef CAS PubMed .
  16. B. H. Drummond, N. Aizawa, Y. Zhang, W. K. Myers, Y. Xiong, M. W. Cooper, S. Barlow, Q. Gu, L. R. Weiss, A. J. Gillett, D. Credgington, Y.-J. Pu, S. R. Marder and E. W. Evans, Nat. Commun., 2021, 12, 4532 CrossRef CAS PubMed .
  17. Y. Li, J.-J. Liang, H.-C. Li, L.-S. Cui, M.-K. Fung, S. Barlow, S. R. Marder, C. Adachi, Z.-Q. Jiang and L.-S. Liao, J. Mater. Chem. C, 2018, 6, 5536–5541 RSC .
  18. G. Hong, C. Si, A. K. Gupta, C. Bizzarri, M. Nieger, I. D. W. Samuel, E. Zysman-Colman and S. Bräse, J. Mater. Chem. C, 2022, 10, 4757–4766 RSC .
  19. A. K. Narsaria, F. Rauch, J. Krebs, P. Endres, A. Friedrich, I. Krummenacher, H. Braunschweig, M. Finze, J. Nitsch, F. M. Bickelhaupt and T. B. Marder, Adv. Funct. Mater., 2020, 30, 2002064 CrossRef CAS PubMed .
  20. S. Kothavale, W. J. Chung and J. Y. Lee, ACS Appl. Mater. Interfaces, 2020, 12, 18730–18738 CrossRef CAS PubMed .
  21. J.-C. Hsueh, F.-E. Szu, Y.-Y. Yu and M.-K. Leung, Org. Biomol. Chem., 2023, 21, 5297–5304 RSC .
  22. B. W. D’Andrade, S. Datta, S. R. Forrest, P. Djurovich, E. Polikarpov and M. E. Thompson, Org. Electron., 2005, 6, 11–20 CrossRef .
  23. C. S. Smithson, D. Ljubic, Y. Wu and S. Zhu, J. Mater. Chem. C, 2015, 3, 8090–8096 RSC .
  24. Y. Huang, M. Jia, C. Li, Y. Yang, Y. He, Y. Luo, Y. Huang, L. Zhou and Z. Lu, Chem. Commun., 2024, 60, 3194–3197 RSC .
  25. S. Reineke, T. C. Rosenow, B. Lüssem and K. Leo, Adv. Mater., 2010, 22, 3189–3193 CrossRef CAS PubMed .
  26. J. H. Lee, H.-Y. Lin, C.-H. Chen, Y.-T. Lee, T.-L. Chiu, J.-H. Lee, C.-T. Chen and C. Adachi, ACS Appl. Mater. Interfaces, 2021, 13, 34605–34615 CrossRef CAS PubMed .

Footnote

† Electronic supplementary information (ESI) available. CCDC 2363088 and 2363089. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4tc02592j
This journal is © The Royal Society of Chemistry 2024