1 Violet-Blue Aggregation-Induced Emission Emitters for Non-Doped Oleds with Ciey Smaller Than 0.046 Pengbo Han, Chengwei Lin, D

Violet-blue Aggregation-induced Emission Emitters for Non-doped OLEDs with CIEy Smaller than 0.046

Pengbo Han, Chengwei Lin, Dongge Ma,* Anjun Qin* and Ben Zhong Tang

P. Han, C. Lin, Prof. D. Ma, Prof. A. Qin, Prof. B. Z. Tang State Key Laboratory of Luminescent Materials and Devices, Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates, Center for Aggregation-Induced Emission, South China University of Technology, Guangzhou, 510640, China. E-mail: [email protected]; [email protected] Prof. B. Z. Tang Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.

Keywords: Aggregation-induced emission, violet-blue emitter, non-doped device, organic light-emitting diode, tetraphenylbenzene

High emission efficiency and finite molecular conjugation in aggregate state are two desirable features in violet-blue emitters. Aggregation-induced emission luminogens (AIEgens) have surfaced as promising luminescent materials that possess both features. Herein, we report the design and synthesis of a group of violet-blue emissive AIEgens with photoluminescence quantum yield higher than 98% in their film states. When utilizing these AIEgens as non- doped emitting layers, the fabricated organic light-emitting diode exhibit a maximum external quantum efficiency of 4.34% with Commission Internationale de L’Eclairage (CIE) coordinates of (0.159, 0.035), which are amenable to next generation Ultra-high Definition

Television (UHDTV) display standard.

1. Introduction

Organic light-emitting diodes (OLEDs) have advanced substantially owing to their outstanding contrast ratio, low driving voltage, flexible display, fast response, etc. in the past decade.[1-5] To date, green, red and blue emitters are being used in the commercial products.[6-8]

However, there is a great challenge that developing efficient and stable violet-blue emitters with Commission Internationale de L’Eclairage (CIE) coordinates (x, y) = (0.131, 0.046), defined by Ultra-high Definition Television (UHDTV) ITU-R BT.2020.[9] 1

In principle, rigid planar structures with finite molecular conjugated skeleton and intrinsic wide bandgap are used for the construction of violet-blue emitters. However, these luminescent materials usually suffer from the aggregation-caused quenching (ACQ) effect due to inevitable intermolecular π-π stacking.[10-13] In addition, their charge transport and charge injection are also unbalanced in OLEDs, which in turn increase driving voltages and decrease device efficiency.[14-17] In consequence, many violet-blue emitters have to be doped into suitable host materials with wide band gap and higher triplet energy. Although the doping device can solve these problems, the device configurations are complicated, making the practical cost increased. To avoid these adverse factors, a strategy of molecularly melding aggregation-induced emission (AIE) core with donor (D) and acceptor (A) is proposed, which has been used for the fabrication of non-doped OLEDs.[18-26] Furthermore, these AIE luminogens (AIEgens) can improve the charge injection and carrier transport in OLEDs, leading to an enhance electroluminescence efficiency of devices when using them as emitting layers.[27-31] However, the reports on the efficient and stable AIEgen-based violet-blue OLEDs with CIEy smaller than 0.046 are rare.

To design violet-blue AIEgens, an AIE core with ultraviolet emission decorated by a weak

D and an A is essential because the core could maintain the violet-blue emission and the D and A groups could slightly red-shift its emission. Following this design principle, tetraphenylbenzene (TPB), a new AIEgen with a solid emission peak at 363 nm, is much suitable for construction violet-blue emitter by attaching D and A groups.[32] When cyano group was used as A and triphenylamine (TPA) or diphenylamine (DPA) moieties as D, the generated AIEgens show high photoluminescence quantum yields. Using these TPB-based

AIEgens as non-doped EMLs, the fabricated OLEDs exhibit excellent device performance.

However, their CIEy values are still larger than 0.08.[33-36]

Above results suggest that there might be a strong intramolecular charge transfer (ICT) between the A and D groups, which induce the emission red-shifted. Thus, to further blue- 2

shift the emission of TPB-based AIEgens, one of the feasible strategies is to decrease the ICT process by weakening the electron accepting or donating ability. In consideration that the cyano group on the TPB core could decrease the lowest unoccupied molecular orbital (LUMO) energy level and reduce electron injection barrier in OLEDs,[37] we thus tried to alter the D group from TPA or DPA to carbazole derivatives with weaker electron donating ability.[38,39]

Furthermore, the carbazole moieties can enhance carrier transport to enhance the device performance.

Following this strategy, we designed and synthesized three TPB derivatives of TPBCzC1-

TPBCzC3 (Figure 1), in which TPB serves as a π-conjugate bridge and is used to reduce the intramolecular interference between D and A groups as well as intermolecular interaction to enhance the emission efficiency in the solid state. The photophysical property investigation in

THF/water mixtures indicates that TPBCzC1-TPBCzC3 show the aggregation-enhanced emission (AEE) with peaks at 409-422 nm. Their emission decreased when the water fractions (fw) in THF/water mixtures are lower than 60% accompanying with red-shifted peaks due to the twisted intramolecular charge transfer (TICT). Afterward, the emission intensified with blue-shifed peaks upon adding water because of the formation of aggregates and activation of restriction of intramolecular motion (RIM) process.[40] Excitingly, these

AIEgens show high photoluminescence (PL) quantum yields (F) over 95% in their film states. As a result, the OLEDs using them as non-doped EMLs exhibit stable device efficiency and violet-blue emission. The TPBCzC1-based OLED achieves a maximum forward-viewing external quantum efficiency (EQE) of 4.34% with CIE coordinates (0.160, 0.035). Meanwhile, the TPBCzC2-based OLED gives a maximum EQE of 4.78% and CIE coordinates of (0.159,

0.060). Thus, this work provides a new guideline for developing violet-blue emitters for next generation UHDTV display standard.

2. Results and Discussion

2.1. Synthesis 3

The synthetic routes to TPBCzC1-TPBCzC3 are shown in Scheme S1. The reagent of 4-(4- bromo-2,5-diphenyl)phenyl-cyanobenzene 1 could be facilely synthesized according to the reported procedures.[35] Then, the Suzuki couplings of 1 and carbazole-subsitituted phenylboronic acid 2 readily furnish TPBCzC1-TPBCzC3 in the yields over 80%. The structures of TPBCzC1-TPBCzC3 were fully characterized by 1H and 13C NMR and high resolution mass (HRMS) spectroscopies, and satisfactory results have also been obtained.

TPBCzC1-TPBCzC3 are soluble in commonly used organic solvents, such as tetrahydrofuran

(THF) and dichloromethane (DCM), but insoluble in water.

2.2. Thermal stability

Thermal and morphological stabilities of the emitters are crucial for the fabrication and operation of OLEDs. Therefore, the thermal properties of TPBCzC1-TPBCzC3 were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods under N2. As shown in Figure S1, TPBCzC1-TPBCzC3 show excellent thermal stabilities

o with the Td (the temperatures for 5% weight loss) as high as 407, 433 and 426 C, respectively.

The glass transition temperatures (Tg) of TPBCzC2 and TPBCzC3 were recorded to be 145

o and 142 C, respectively, while no apparent Tg peak could be detected for TPBCzC1.

o Moreover, TPBCzC3 exhibits evident Tc (crystallization temperature) at 238 C. These data reveal that TPBCzC1-TPBCzC3 are suitable for OLED fabrication by vacuum thermal evaporation technique.

2.3. Photophysical Properties

After confirming the structures and studying the thermal stabilities of TPBCzC1-TPBCzC3, we investigated their photophysical properties. Figure 2A presents the UV-vis spectra of

TPBCzC1-TPBCzC3 in THF solutions with a concentration of 10 μM. They show similar profiles with absorption bands in the range of 200 to 320 nm. The absorption bands located at

200-260 nm are considered as the π–π∗ transition of TPB,[9] whereas, the long-wavelength absorption at 320 nm might be attributed to effective ICT transition.[35] From the onset of 4

absorptions of TPBCzC1-TPBCzC3 in THF solutions, the optical bandgap (Eg) levels were deduced to be 3.52, 3.43, 3.42 eV, respectively (Table 1).

The PL spectra of TPBCzC1-TPBCzC3 in THF solutions with a concentration of 10 μM and their evaporated films are shown in Figures S2 and 2B. In THF solutions, TPBCzC1-

TPBCzC3 emit at violet-blue and deep-blue regions with peaks at 429, 420 and 438 nm, suggesting that the substitution greatly affects the PL. In the vacuum-deposited neat films,

TPBCzC1-TPBCzC3 show violet-blue emission peak at 411, 409 and 426 nm, respectively. In contrast with a single molecule in THF solutions, the emission peaks of TPBCzC1-TPBCzC3 films were considerably blue-shifted, implying that a shorter conjugation length in the solid

[41] state than that in solution. Notably, the ΦF values of TPBCzC1-TPBCzC3 in THF solutions were recorded to be 81.3, 86.9 and 94.5%, whereas, those in vacuum-deposited neat films are enhanced to be 99.9, 98.9 and 98.6%, respectively, indicating that they possess typical AEE feature.

To further confirm the AEE feature of TPBCzC1-TPBCzC3, their PL spectra were conducted in THF/water mixtures with different water fractions. As shown in Figures 3 and

S3, the PL intensity of TPBCzC1-TPBCzC3 keeps decreasing and slowly red-shifting upon

[42] adding water, which is ascribed to the TICT effect. With further increasing fw, their PL gradually blue-shifted along with the increase in intensity owing to the formation of

[40] aggregates and in turn activating the process of RIM. Moreover, the PL lifetime (τd) of

TPBCzC1-TPBCzC3 films fabricated by vacuum evaporation were measured to be to 2.05,

2.12 and 1.92 ns, respectively, suggesting that they emit fluorescence (Figure S4).

2.4. Single crystal analysis

The single crystal of TPBCzC3 (CCDC 1988577) was grown successfully from DCM/n- hexane mixtures by slow solvent evaporation and analyzed by X-ray diffraction crystallography. As depicted in Figure 4A, a planar conformation with small angles in the range of 18-28° was observed in the direction of the long molecular axis of TPBCzC3, while 5

peripheral phenyl groups of TPB core exhibit a twisted conformation with a large dihedral angle of 53°. In addition, the twist angle is recorded to be 57° at the N-position of carbazole group. Thanks to the twisted peripheral phenyl groups of TPBCzC3, no close π-π stacking was found. However, the antiparallel arrangement and strong intermolecular C-H ⋯ N interference with a short distance of 2.587 Å exit between the molecules (Figure 4B).

Moreover, multiple intermolecular C-H⋯π hydrogen bonds with distances of 2.723-3.789 Å were also observed in adjacent molecules. These intermolecular interactions can effectively rigidify molecular conformation and reduce non-radiative energy dissipation in the aggregate state, making the AIEgen emit brightly in the aggregate and film states.[43]

2.5. Electronic Structures

TPBCzC1-TPBCzC3 were subjected to density functional theory (DFT) calculations using a

B3LYP/6-31G(d,p) basis set to decipher the relationship between structure and photophysical property. The optimized ground state (S0) geometries of TPBCzC1-TPBCzC3 were plotted in

Figure 5. The dihedral angle between the different carbazole donor groups and adjacent units are calculated to be 53.8, 54.5, 36.7 °C for TPBCzC1-TPBCzC3, respectively, indicating that they adopt a twisted molecular configuration. These structural features can interrupt intermolecular π-π stacking interactions, and make the AIEgens emit strongly in their film states. The electron cloud distributions of these AIEgens are mainly concentrated on TPB core and cyano unit in the LUMO and on the carbazole unit in the highest occupied molecule orbital (HOMO). Apparently, the spatial overlap of HOMO and LUMO could result in effective ICT transition, which is also confirmed by the long-wavelength absorption of

TPBCzC1-TPBCzC3 at 320 nm. The theoretically calculated energy levels of HOMO and

LUMO for TPBCzC1-TPBCzC3 were also obtained. As shown in Figure 5, large bandgaps for these AIEgens are deduced, leading them to emit in the violet-blue region.

2.6. Electrochemical Behaviors

Besides above theoretical calculation, we also measured the electrochemical properties of

TPBCzC1-TPBCzC3 to obtain their practical LUMO and HOMO energy levels by cyclic voltammetry (CV) in DCM containing 0.1 M tetra-n-butylammonium hexafluorophosphate.

As shown in Figure S5, the onset oxidation potentials (Eonset) of TPBCzC1-TPBCzC3 are at

0.94, 1.03, 0.98 V, respectively. According to the equation of HOMO = −(Eonset + 4.4) eV, the HOMO energy levels of them were deduced to be -5.34, -5.43 and -5.38 eV, respectively.

The LUMO energy levels of TPBCzC1-TPBCzC3 were thus calculated to be -1.82, -2.00 and

-1.96 eV, respectively, from the equation of LUMO = (HOMO +Eg) eV. Notably, the LUMO energy levels of TPBCzC1-TPBCzC3 are higher than that of TmPyPB, a traditional electron- transporting material (LUMO = −2.7 eV), suggesting that the electron injection from

TmPyPB to these AIEgens is feasible.

2.7. Non-doped Violet-blue OLEDs

Thanks to their excellent thermal stabilities and high emission efficiency, TPBCzC1-

TPBCzC3 were used as non-doped EMLs to construct OLEDs with a configuration of ITO/

HATCN (5 nm)/TAPC (50 nm)/EBLs (5 nm)/EMLs (20 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al.

In these devices, ITO, 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN), 1-bis[4-

[N,N-di(4-tolyl)amino]phenyl]-cyclohexane (TAPC) and 1,3,5-tri[(3-pyridyl)-phen-3- yl]benzene (TmPyPB) act as the anode, hole injection, hole-transporting and electron- transporting layers, respectively. 1,3-Bis(N-carbazolyl)benzene (mCP) was chosen for exciton-blocking layers (EBLs) for TPBCzC1-based OLED, whereas, 4,4',4''-tri(N- carbazolyl)-triphenylamine (TCTA) was used as EBLs when TPBCzC2 and TPBCzC3 were acted as EMLs, that is, device B1 refers to the EBL is mCp and EML is TPBCzC1; B2: EBL:

TCTA and EML: TPBCzC2; B3: EBL: TCTA and EML: TPBCzC3. As depicted in Figures 6 and S6, the non-doped devices could be turned on at a low voltage, and the devices B2 and B3 exhibit maximum EQE of 4.78% and 2.76% with CIE coordinates of (0.159, 0.060) and

(0.167, 0.070), respectively. Notably, the non-doped TPBCzC1-based OLED achieves a 7

maximum EQE of 4.34% with small CIE coordinates of (0.160, 0.035). Thus, we successfully fabricated a non-doped violet-blue AIEgen-based OLED with CIEy < 0.046 for the first time.

It is also worth noting the outstanding EQE value of the TPBCzC1-baesd OLED also represents the best results for violet-blue OLEDs with CIEy < 0.046 based on fluorescent materials (Figure 6C and Table 2).[44-49] Moreover, all devices exhibit a very low efficiency roll-off probably because the radiative transition channels are activated and the non-radiative transition channels are inhibited in the aggregate state, confirming the excellent efficiency stabilities of the devices (Figures 6A and S7).

3. Conclusion

Novel TPB-based molecules of TPBCzC1-TPBCzC3, in which the carbazole derivatives serve as electron donor and cyano groups as an electron acceptor, were rationally designed and facilely synthesized. TPBCzC1-TPBCzC3 are AEE-active and thermally stable. They show efficient violet-blue emission with high PLQY closing 100% in their film states. Based on their superior properties, non-doped violet-blue OLEDs were fabricated by utilizing

TPBCzC1-TPBCzC3 as non-doped EMLs. Among them, the TPBCzC1-based OLED exhibits a high EQE of 4.34% with CIE coordinates of (0.160, 0.035), which represents the first example of non-doped violet-blue AIEgen-based OLED with CIEy smaller than 0.046.

Meanwhile, the TPBCzC2-based OLED also achieves a maximum EQE of 4.78% and CIE coordinates of (0.159, 0.060). This work provides a practical molecular design strategy for violet-blue emitters, which is crucial for next generation UHDTV display standard.

4. Experimental Section

Synthesis of 4'-(4-(9H-carbazol-9-yl)phenyl)-5'-phenyl-[1,1':2',1''-terphenyl]-4-carbonitrile

(TPBCzC1)

Phenylboronic acid derivative 2a (700 mg, 1.71 mmol), anhydrous potassium carbonate

(980 mg, 3.41 mmol) and Pd(PPh3)4 (99 mg, 0.09 mmol) were added into a 100 mL two necked round bottom flask under N2, then 1,4-dioxane (14 mL) and water (2 mL) were 8

injected into the flask. The 1 (700 mg, 1.71 mmol) dissolved in 6 mL 1,4-dioxane was added dropwise into the flask within 3.0 h. The reaction solution was stirred at 80 oC for 10 h. After cooling to room temperature, the solution was poured into water and extracted with DCM for three times, and then organic phases were combined and dried over anhydrous magnesium sulfate. After filtration and solvent evaporation, the residue was purified by a silica gel column chromatography using petroleum ether (PE)/DCM (1:1 v/v) as eluent. White solid of

1 TPBCzC1 was obtained in 80% yield (783 mg). H NMR (500 MHz, CD2Cl2), δ (TMS, ppm):

8.16 (m, 1H), 8.14 (m, 1H), 7.69 (s, 1H), 7.58 (d, 2H), 7.56 (m, 1H), 7.47 (d, 4H), 7.45-7.38

13 (m, 6H), 7.35-7.25 (m, 12H). C NMR (125 MHz, CD2Cl2), δ (TMS, ppm): 145.87, 140.77,

140.47, 140.19, 140.15, 139.94, 139.90, 138.18, 136.33, 132.99, 132.69, 131.82, 129.94,

129.88, 128.28, 128.17, 127.14, 127.09, 126.51, 125.94, 123.31, 120.19, 119.94, 118.84.

+ HRMS (C43H28N2): m/z 572.2271 (M , calcd 572.2252).

Synthesis of 4'''-(9H-carbazol-9-yl)-2',5'-diphenyl-[1,1':4',1'':4'',1'''-quaterphenyl]-4- carbonitrile (TPBCzC2)

TPBCzC2 was synthesized by similar procedures as TPBCzC1 from the reagents of 1 and

1 2b in 82% yield. H NMR (500 MHz, CD2Cl2), δ (TMS, ppm): 8.15 (d, 2H), 7.84 (d, 2H),

7.63 (m, 5H), 7.54 (m, 3H), 7.44 (t, 4H), 7.36 (m, 4H), 7.29 (m, 10H), 7.22 (d, 2H). 13C NMR

(125 MHz, CD2Cl2), δ (TMS, ppm): 145.31, 140.22, 140.10, 139.54, 139.28, 138.89, 137.96,

137.37, 136.30, 132.49, 132.18, 130.00, 129.87, 129.28, 127.66, 127.57, 126.51, 126.36,

126.00, 125.38, 122.76, 119.63, 119.38, 118.25, 109.18. HRMS (C49H32N2): m/z 648.2540

(M+, calcd 648.2565).

Synthesis of 5'-phenyl-4'-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-[1,1':2',1''-terphenyl]-4- carbonitrile (TPBCzC3)

TPBCzC3 was synthesized by similar procedures as TPBCzC1 from the reagents of 1 and

1 2c in 85% yield. H NMR (500 MHz, CD2Cl2), δ (TMS, ppm):8.39 (s, 1H), 8.19 (d, 1H),

7.69-7.59 (m, 8H), 7.56-7.43 (m, 7H), 7.38-7.28 (m, 13H), 7.23 (m, 2H). 13C NMR (125 MHz, 9

CD2Cl2), δ (TMS, ppm): 145.37, 140.24, 139.69, 139.23, 137.18, 132.53, 132.17, 131.19,

130.01, 129.72, 129.34, 129.29, 127.64, 127.55, 126.95, 126.30, 126.00, 119.69, 119.49,

+ 118.27, 117.83, 109.80, 109.33. HRMS (C49H32N2): m/z 648.2543 (M , calcd 648.2565).

Supporting Information Supporting Information is available from the Online Library or from the author.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (21788102 and 21525417), the Natural Science Foundation of Guangdong Province (2019B030301003 and 2016A030312002), and the Innovation and Technology Commission of Hong Kong (ITC-CNERC14S01).

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Figure 1. Design principle, chemical structures of violet-blue AIEgens.

A B TPBCzC1 TPBCzC1 TPBCzC2 TPBCzC2 TPBCzC3 TPBCzC3

PL intensity PL (au)

Absorbance (au) Absorbance

200 250 300 350 400 450 350 400 450 500 550 600 Wavelength (nm) Wavelength (nm) Figure 2. (A) UV-vis (THF solution) and (B) photoluminescence (PL, films) spectra of TPBCzC1-TPBCzC3.

A B f (vol%) fw (vol%) w 90 90 80 80 60 60 40 40 20 20 0 0

PL intensity (au) intensity PL (au) intensity PL

350 400 450 500 550 350 400 450 500 550

Wavelength (nm) Wavelength (nm)

1.5

C D

fw (vol%) TPBCzC1 90 TPBCzC2 80 TPBCzC3 60 1.2 40 20 0

I 0.9

PL intensity (au) intensity PL 0.6

0.3 350 400 450 500 550 0 20 40 60 80 100 Wavelength (nm) Water fraction (%) Figure 3. (A) PL spectra of TPBCzC1, (B) TPBCzC2 and (C) TPBCzC3 in THF/water mixtures with different water fractions. (D) Plots of I/I0 of TPBCzC1-TPBCzC3 versus water fractions in THF/water mixtures. ex: 320 nm; concentration: 10 μM. 14

Figure 4. (A) ORTEP drawing of the crystal structure (CCDC 1988577) of TPBCzC3. (B) Packing pattern of TPBCzC3 in crystal states.

Figure 5. Molecular orbital amplitude plots and energy levels of TPBCzC1-TPBCzC3 calculated by B3LYP/6-31G(d,p).

5 1 10 A B C 1.0 This work

0.8 4

100 0.6 3 This work

EQE (%) EQE (%) Ref. [44] B1 0.4 B1 10-1 Ref. [45] B2 B2 2 Ref. [46] B3 B3 Ref. [47] 0.2

Normalized Intensity (au) Ref. [48] Ref. [49]

10-2 0.0 1 1 10 100 1000 400 450 500 550 600 0.01 0.02 0.03 0.04 0.05 Luminance (cd m-2) Wavelength (nm) CIEy Figure 6. (A) External quantum efficiencies as a function of luminance of the resultant non- doped violet-blue OLEDs with different EBLs and emitters. Inset: the emission of device B1. (B) Electroluminescence (EL) spectra of B1-B3 at 5.0 V. (C) Maximum EQE values of the representative violet-blue OLEDs with CIEy smaller than 0.046 based on fluorescent materials. Device B1: EBL: mCP and EML: TPBCzC1; B2: EBL: TCTA and EML: TPBCzC2; B3: EBL: TCTA and EML: TPBCzC3.

Table 1. Photophysical, thermal and electronic properties of TPBCzC1-TPBCzC3

c) d) λPL [nm] ΦF [%] τ [ns] λ a) T /T /T HOMO/LUMOe E f AIEgens abs d g c g [nm] [°C] [eV] [eV] sola) filmb) sola) filmb) sola) filmb)

TPBCzC1 320 429 411 81.3 99.9 2.33 2.05 407/-/- -5.49/-1.97 3.52

TPBCzC2 320 420 409 86.9 98.9 1.64 2.12 432/145/238 -5.69/-2.26 3.43

TPBCzC3 320 438 426 94.5 98.6 1.88 1.92 426/142/- -5.56/-2.14 3.42 a) Measured in oxygen-free THF solution at room temperature with concentration of 10-5 M. b) Measured in c) d) evaporated film. Absolute PL quantum yield (F). PL lifetimes at room temperature under air conditions. e) Measured by cyclic voltammetry. f) Estimated from absorption onset.

Table 2. EL performance of TPBCzC1-TPBCzC3 based non-doped voilet-blue OLEDs and summary of reported OLED with CIEy < 0.046.

b a b a a Device Compound [reference] Von(V) CIE (x, y) EQE (%) λmax (nm) CE (cd/A) PE (lm/W)

B1 TPBCzC1 [This work] 3.4 (0.160, 0.035) 4.34/3.90 422 0.95/0.87 0.85/0.47

B2 TPBCzC2 [This work] 3.4 (0.159, 0.060) 4.78/4.59 423 2.01/1.95 1.57/1.41

B3 TPBCzC3 [This work] 3.8 (0.167, 0.070) 2.76/2.24 405 1.07/0.87 0.81/0.55

- TPA-S[44] 3.0 (0.158, 0.039) 1.76/- 423 0.47/0.45 0.32/-

PIMNA[45] 3.8 (0.160, 0.034) 2.43/2.42 412 0.51/- -

- TAZ-4Cz[46] 3.9 (0.160,0.040) 2.48 412 0.65/- 0.58/-

- TPI-Bz[47] 3.2 (0.162,0.043) 1.5/- 420 0.5/- 0.45/-

- TNa-PI[48] 3.4 (0.157,0.041) 2.63/2.40 428 0.87/0.80 0.73/0.36

- tDIDCz[49] 3.5 (0.164,0.019) 3.3/1.3 402 - - a) Order of maximum, then values at 100 cd m-2; b) measured at 100 cd m-2. Device configuration: B1 (EML: TPBCzC1): ITO/HATCN(5 nm)/TAPC(50 nm)/mCP (5 nm)/EML (20 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al; B2 (EML: TPBCzC2) and B3 (EML: TPBCzC3): ITO/HATCN(5 nm)/TAPC(50 nm)/TCTA(5 nm)/EML (20 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al.

The table of contents

Keyword: Aggregation-induced emission, violet-blue emitters, non-doped device, organic light-emitting diodes, tetraphenylbenzene

Pengbo Han, Chengwei Lin, Dongge Ma,* Anjun Qin* and Ben Zhong Tang

Violet-blue Aggregation-induced Emission Emitters for Non-doped OLEDs with CIEy Smaller than 0.046

A series of violet-blue AIEgens with high emission efficiency in solid state are developed. Organic light-emitting diode (OLED) with TPBCzC1 as a non-doped emitting layer exhibits a high EQE of 4.34% with small CIE coordinates of (0.160, 0.035), which is the first example of non-doped violet-blue AIEgen-based OLED with CIEy smaller than 0.046.

Supporting Information

Violet-blue Aggregation-induced Emission Emitters for Non-doped OLEDs with CIEy Smaller than 0.046

Pengbo Han, Chengwei Lin, Dongge Ma,* Anjun Qin* and Ben Zhong Tang

Materials and Instruments

All the chemicals and reagents were purchased from commercial sources and used as received without further purification. 1H and 13C NMR spectra were measured on a Bruker AV 500 spectrometer in deuterated dichloromethane. High resolution mass spectra (HRMS) were recorded on a GCT premier CAB048 mass spectrometer operating in MALDI-TOF mode.

TGA analysis was carried out on a TA TGA Q5000 and DSC analysis was performed on a

DSC Q1000 under dry nitrogen at a heating rate of 10 oC min-1. UV-vis absorption spectra were measured on a Shimadzu UV-2600 spectrophotometer. Photoluminescence spectra were recorded on a Horiba Fluoromax-4 spectrofluorometer. Fluorescence quantum yields were measured using a Hamamatsu absolute PL quantum yield spectrometer C11347

Quantaurus_QY. Fluorescence lifetimes were determined with a Hamamatsu C11367-11

Quantaurus-Tau time-resolved spectrometer. The frontier orbitals of the molecules based on the ground state geometries were calculated at B3LYP/6-31G(d,p) by Gaussian 09 program.

Cyclic voltamogramms were measured on a CHI 610E A14297 in a solution of tetra-n- butylammonium hexafluorophosphate (Bu4NPF6) (0.1 M) in dichloromethane at a scan rate of

100 mV s-1.

Scheme S1. Synthetic routes to TPBCzC1-TPBCzC3.

A B 100

T : 238 °C 80 c

Tg: 145 C 60 Td(C)

TPBCzC1 407 TPBCzC2 433 40 Tg: 142 C 426 Endotheomo

Weight (%) Weight TPBCzC3

TPBCzC1 20 TPBCzC2 TPBCzC3

0 100 200 300 400 500 600 100 150 200 250 Temperature (C) Temperature (C) Figure S1. (A)TGA thermograms and (B) DSC curve of TPBCzC1-TPBCzC3 recorded under nitrogen at a heating rate of 10 oC/min.

TPBCzC1 TPBCzC2 TPBCzC3

PL intensity (au)

350 400 450 500 550 600

Wavelength (nm) Figure S2. PL spectra of TPBCzC1-TPBCzC3 in THF solutions. ex: 320 nm; concentration: 10 μM.

A fw (vol%) 90 80 70 60 50 40 30 20 10 0

PL intensity (au) intensity PL

350 400 450 500 550 Wavelength (nm)

B fw (vol%) 90 80 70 60 50

40 30 20 10 0

PL intensity (au) intensity PL

350 400 450 500 550 Wavelength (nm)

C fw (vol%) 90 80 70 60 50 40 30 20 10 0

PL intensity (au) intensity PL

350 400 450 500 550 Wavelength (nm) Figure S3. (A) PL spectra of TPBCzC1, (B) TPBCzC2 and (C) TPBCzC3 in THF/water mixtures with different water fractions. ex: 320 nm; concentration: 10 μM.

TPBCzC1 1000 TPBCzC2 TPBCzC3

100

PL intensity (au)

1 0 50 100 150 200

Time (ns) Figure S4. Fluorescence lifetime decays of evaporated films of TPBCzC1-TPBCzC3.

TPBCzC1 TPBCzC2 TPBCzC3

Curren

0.0 0.4 0.8 1.2 1.6 Potential(V) Figure S5. Cyclic voltammograms of TPBCzC1-TPBCzC3 measured in dichloromethane containing 0.1 M tetra-n-butylammonium hexafluorophosphate.

250

) 3

-2 10 200 B1

)

B2 -2

mA cm B3 2 ( 150 10

cd m

(

100 101 50

Luminance

Current Density 0 100 0 2 4 6 8 Voltage (V) Figure S6. Current efficiency and luminance as a function of voltage of the resultant violet- blue OLEDs.

10 101 A B

)

-1

-1 1 100

0.1 10-1 B1 B1 B2 B2

B3 Power Efficiency (lm W

Current Efficiency (cd A B3

0.01 10-2 1 10 100 1000 1 10 100 1000 Luminance (cd m-2) Luminance (cd m-2) Figure S7. Forward-viewing (A) CE and (B) PE as a function of luminance for devices B1- B3