Supplementary Information Dihedral Angle Control of Blue Thermally- Activated Delayed Fluorescent Emitters through Donor Substitution Position for Efficient Reverse Intersystem Crossing Chan Seok Oh 1, Daniel de Sa Pereira 2*,Si Hyun Han 1, Hee-Jun Park 1, Heather F. Higginbotham 2, Andrew P. Monkman 2, Jun Yeob Lee 1* 1 School of Chemical Engineering, Sungkyunkwan University 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, 440-746, Korea 2 Department of Physics, Durham University South Road, Durham, DH1 3LE, United Kingdom Authors with equal contribution (Chan Seok Oh 1 and Daniel de Sa Pereira 2 contributed equally) Corresponding Author: daniel.a.pereira@durham.ac.uk leej17@skku.edu S-1
S1. Materials and synthesis 9,9'-(3-Bromo-1,2-phenylene)bis(9-carbazole) 1-Bromo-2,3-difluorobenzene (1.00 g, 5.13 mmol), 9H-carbazole (1.91 g, 11.29 mmol), and cesium carbonate (4.18 g, 12.82 mmol) were dissolved in dimethylformamide (40 ml). The mixture was stirred and refluxed for 10 h, then the mixture was cooled to room temperature. The crude solution was extracted using dichloromethane and distilled water, and then the organic layer was concentrated. The crude material was purified by column chromatography using a mixed eluent (dichloromethane: n-hexane = 1 : 6). A white solid product was collected (2.2 g, 88 % yield). 1H NMR (400 MH Z, CDCl 3) : δ 8.04 (d, J=4.80 Hz, 1H), 7.76-7.73 (m, 5H), 7.65 (t, J=8.40 MHz, 12H), MS (API-) m/z: 487.4 [(M + H) - ]. 9,9'-(4-Bromo-1,3-phenylene)bis(9-carbazole) Synthetic method of 9,9'-(4-bromo-1,3-phenylene)bis(9-carbazole) was the same as that of 9,9'- (3-bromo-1,2-phenylene)bis(9-carbazole). 1-Bromo-2,4-difluorobenzene (1.00 g, 5.13 mmol) was used as a starting material. A white solid product was obtained after purification (2.0 g, 80 % yield). 1H NMR (400 MH Z, CDCl 3) : δ 8.19-8.10 (m, 5H), 7.77 (d, J=1.20 Hz, 1H), 7.71 (d, J=5.80 Hz, 1H), 7.53-7.42 (m, 6H), 7.36-7.30 (m, 4H) 7.24 (d, J=4.20, 2H) MS (API-) m/z: 487.4 [(M + H) - ]. 9,9'-(2-Bromo-1,4-phenylene)bis(9-carbazole) Synthetic method of 9,9'-(2-bromo-1,4-phenylene)bis(9-carbazole) was the same as that of 9,9'- (3-bromo-1,2-phenylene)bis(9-carbazole). 1-Bromo-1,4-difluorobenzene (1.00 g, 5.13 mmol) was used as a reagent. A white solid product was collected (1.9 g, 76 % yield). S-2
1H NMR (400 MH Z, CDCl 3) : δ 8.22-8.19 (m, 4H), 8.15 (d, J=1.20 Hz, 1H), 7.82-7.80 (m, 1H), 7.75 (d, J=4.0 Hz, 1H), 7.48 (d, 2H), 7.54-7.48 (m, 4H), 7.40-7.38 (m, 4H), 7.25 (d, J=4.0 Hz, 2H) MS (API-) m/z: 487.4 [(M + H) - ]. 2-(3,4-Difluorophenyl)-4,6-diphenyl-1,3,5-triazine 2-Chloro-4,6-diphenyl-1,3,5-triazine (1.00 g, 3.70 mmol), (3,4-difluorophenyl)boronic acid (0.65 g, 4.07 mmol), potassium carbonate (1.53 g, 11.09 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.13 g, 0.11 mmol) were dissolved in tetrahydrofuran (45 ml) and distilled water (15 ml). The mixture was stirred and refluxed for 6 h, then the mixture was cooled to room temperature and was separated using dichloromethane and distilled water. The dichloromethane layer was concentrated and purified by recrystallization in a mixed solvent of dichloromethane and ethanol. A white solid product was collected after recrystallization (0.8 g, 63 % yield). 1H NMR (400 MH Z, CDCl 3) : δ 8.76-8.58 (m, 6H), 7.60 (s, 6H), 7.36 (s, 1H) m/z: 345.8 [(M + H) - ]. 9,9'-(3-(4,6-Diphenyl-1,3,5-triazin-2-yl)-1,2-phenylene)bis(9-carbazole) (23CT) 9,9'-(2-Bromo-1,3-phenylene)bis(9-carbazole) (1.00 g, 2.05 mmol) was dissolved in anhydrous tetrahydrofuran (30 ml) and the mixture was cooled to -70 o C. n-butyllithium solution (1.64 ml, 2.5 M) was slowly injected into the mixture and the mixture was stirred for 1 h after addition of trimethyl borate (0.55 ml, 4.51 mmol). The reactants were stirred for an additional 12 h and was quenched with 10 % hydrochloric acid. The reaction mixture was extracted using dichloromethane and water followed by evaporation of dichloromethane. A solid product (0.65 g, 70 % yield) was purified by column chromatography using a dichloromethane eluent. The (2,3-di(9-carbazol-9-yl)phenyl)boronic acid (0.60 g, 1.31 mmol) was mixed with 2-chloro-4,6- diphenyl-1,3,5-triazine (0.39 g, 1.45 mmol), potassium carbonate (0.54 g, 3.94 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.05 g, 0.04 mmol) in a mixed solvent of S-3
tetrahydrofuran (30 ml) and distilled water (10 ml). The mixture was stirred and refluxed for 12 h, then the mixture was cooled down to room temperature followed by extraction using dichloromethane and distilled water. The dichloromethane layer was separated followed by evaporation of the solvent. A solid product was purified by column chromatography using a mixed eluent (dichloromethane : n-hexane = 1 : 8). Final product was obtained as a yellowish white solid by sublimation (0.45 g, 54 % yield). 1H NMR (500 MH Z, CDCl 3) : δ 8.50 (d, J=3.80 Hz, 1H), 7.98-7.91 (m, 6H), 7.83 (d, J=4.25 Hz, 2H), 7.58 (d, J=3.75 Hz, 2H), 7.44 (t, J=8.00 Hz, 2H), 7.29-7.24 (m, 6H), 7.13 (d, J=4.00 Hz, 2H0, 7.10-7.04 (m, 4H), 6.99 (t, J=8.50 Hz, 2H), 6.92 (t, J=7.50 Hz, 2H) 13 C NMR (125 MH Z, CDCl 3) : δ 140.79, 140.71, 139.26, 137.37, 135.44, 134.63, 133.40, 132.58, 132.34, 129.66, 128.92, 128.54, 125.59, 125.50, 123.88, 123.71, 120.14, 120.08, 119.73, 110.08, 109.75 MS (API-) m/z: 640.3 [(M + H) - ]. 9,9'-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9-carbazole) (24CT) Synthetic method of 24CT was the same as that of 23CT. 24CT was obtained as a yellowish power after sublimation (0.62 g, 74 % yield). 1H NMR (500 MH Z, CDCl 3) : δ 8.81 (d, J=4.00 Hz, 1H), 8.16 (d, J=4.00 Hz, 2H), 8.17-7.99 (m, 8H), 7.68 (d, J=4.00 Hz, 2H), 7.48 (t, J=8.50 Hz, 4H), 7.36-7.32 (m, 10H), 7.24-7.21 (m, 2H) 13 C NMR (125 MH Z, CDCl 3) : δ 141.96, 141.70, 140.38, 138.65, 135.58, 134.60, 134.57, 132.64, 128.97 128.58, 128.42, 126.70, 126.60, 126.37, 124.17, 123.84, 121.01, 120.76, 120.55, 120.04, 109.99, 109.61 MS (API-) m/z: 640.3 [(M + H) - ]. 9,9'-(2-(4,6-Diphenyl-1,3,5-triazin-2-yl)-1,4-phenylene)bis(9-carbazole) (25CT) Synthetic method of 25CT was the same as that of 23CT. 25CT was obtained as a yellowish power after sublimation (0.59 g, 70 % yield). 1H NMR (500 MH Z, CDCl 3) : δ 8.79 (d, J=1.25 Hz, 1H), 8.22 (d, J=3.75 Hz, 2H), 8.07-8.03 (m, 3H), 7.99-7.95 (m, 5H), 7.20 (d, J=4.00 Hz, 2H), 7.52 (t, J=8.25 Hz, 2H), 7.43 (t, J=1.25 Hz, 2H), 7.39- S-4
7.34 (m, 6H), 7.29-7.22 (m, 6H) 13 C NMR (125 MH Z, CDCl 3) : δ 171.66, 171.58, 141.86, 140.83, 138.35, 137.94, 135.65, 135.40, 132.67, 132.39, 131.14, 130.72, 128.97, 128.55, 126.51, 126.31, 123.96, 123.81, 120.75, 120.54, 120.02, 110.02, 109.72 MS (API-) m/z: 640.3 [(M + H) - ]. 9,9'-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)-1,2-phenylene)bis(9-carbazole) (34CT) 2-(3,4-Difluorophenyl)-4,6-diphenyl-1,3,5-triazine (1.00 g, 2.87 mmol), 9H-carbazole (1.07 g, 6.31 mmol), and cesium carbonate (2.34 g, 7.17 mmol) was dissolved in dimethylformamide (40 ml). The mixture was refluxed for 12 h under stirring. The mixture was cooled down to room temperature and was extracted using dichloromethane and distilled water. The dichloromethane layer was separated and concentrated by evaporation. A crude product was purified by column chromatography using a mixed eluent (dichloromethane: n-hexane = 1 : 8). A yellowish white solid product was collected after sublimation (1.10 g, 60 % yield). 1H NMR (400 MH Z, CDCl 3) : δ 8.73 (d, J=4.80 Hz, 4H), 8.26 (t, J=7.60 Hz, 1H), 7.63-7.55 (m, 6H), 6.88-6.82 (m, 2H), 4.01 (s, 3H) 13 C NMR (100 MH Z, CDCl 3) : δ 139.93, 139.76, 138.04, 137.19, 136.05, 134.65, 133.00, 131.27, 130.83, 129.26, 128.94, 125.75, 125.70, 123.86, 123.68, 120.39, 120.22, 120.11, 109.96, 109.82 MS (API-) m/z: 640.3 [(M + H)-]. The single crystal structure of CT34 was determined by 2D SMC beam line at Pohang Accelerator Laboratory(Pohang, Korea) using monochromatic synchrotron radiation. S-5
S2. risc constant calculations The calculation for the rate constants of the intersystem crossing, and reverse intersystem crossing, processes presented in this manuscript were conducted following the fundamental TADF mechanism presented by Dias et. al in 1.The fluorescence yield of TADF emitters (Ф F ) is the result of the fluorescent decay of the of the singlet in the prompt, Ф, and delayed, Ф, intervals as a multistep triplet harvesting as shown in equation 1. Ф =Ф +Ф = Ф Ф Ф 1 =Ф 1 1 Ф Ф Where Ф and Ф are the intersystem crossing (ISC) and reverse ISC (risc) yields, respectively. The ratio between Ф and Ф is usually calculated to perceive Ф Ф. It can be determined according to the equation 2 considering the integrated area in the DF ( ) and PF ( ) regions. Ф /Ф = 2 In good TADF systems, the Ф /Ф is above 4 1, the product Ф Ф is above 0.8, so Ф can be assumed to be 1. Therefore, equation 1 can be simplified to: Ф = Ф /Ф 1+Ф /Ф 3 With the decay curves, the lifetimes of the prompt, and delayed,, can be determined by fitting and all the rate constants calculated with equations 4 and 5: = Ф = 1 Ф /Ф 1+Ф /Ф 4 = 1 1 1 Ф = 1 1+Ф /Ф 5 S-6
Figure S3. Cyclic voltammetry of 26CT, 23CT, 24CT, 25CT, 34CT and 35CT. Experimental details: The HOMO energy level was determined using an IVIUM STAT in three electrodes with a carbon working electrode, a platinum wire counter electrode, and an Ag/AgCl reference electrode. The LUMO energy level was determined after nitrogen bubbling to remove oxygen from the sample. Ferrocene was used as the standard material for the cyclic voltammetry measurement. Tetrabutylammonium perchlorate dissolved in acetonitrile at 0.1 M concentration was used as electrolyte. S-7
Figure S4. Solvent effects on the charge transfer (CT) absorption bands of a) 24CT and b) 34CT in solvents with increased polarity: methylcyclohexane (MCH), toluene and dichloromethane (DCM). 24CT shows a mixture of both n-π* and π-π* characters while the hypsochromic shift in 34CT corresponds to a n-π* transition. Normalised Absorption 1.2 1.0 0.8 0.6 0.4 0.2 0.0 a) MCH Toluene DCM 24CT 320 340 360 380 400 Wavelength (nm) Normalised Absorption 1.2 b) 1.0 0.8 0.6 0.4 34CT MCH 0.2 Toluene DCM 0.0 320 340 360 380 400 Wavelength (nm) S-8
Figure S5. Energy levels and corresponding energy gaps of each emitter used in this study divided into the three delayed fluorescence (DF) regimes: fast, medium and slow. Each value was taken from the onset of the photoluminescence (PL) and phosphorescence (PH) spectra. 1 CT (+/- 0.02 ev) 3 LE (+/- 0.02 ev) E ST (+/- 0.02 ev) 26CT 3.05 3.12-0.07 Fast 23CT 2.98 3.00-0.02 DF 24CT 3.01 2.90 0.11 Medium 25CT 2.97 2.90 0.07 DF 34CT 3.14 2.85 0.29 Slow 35CT 3.20 2.96 0.24 DF S-9
Figure S6. Decay rates of the prompt ( red) and delayed ( green) fluorescence of all -ortho based isomers, a) 26CT, b) 23CT, c) 24CT and d) 25CT. The expression used in the single and double exponential fittings is shown below. All fittings obtained are in nanoseconds. Finally, the last table shows the lifetimes of and divided into their correspondent DF regime: fast and medium. Fast DF isomers showed mono-exponential DF whereas medium DF isomers showed bi-exponential decays resulting in 1 and 2 decays in the DF region, respectively. Single Exponential Decay Double Exponential Decay = + exp = + exp + exp Isomer (ns) (µs) 1 (µs) 2 26CT 3.1 ± 0.1 16.4 ± 0.9 ----------- Fast 23CT 8.4 ± 0.8 8.7 ± 0.3 ----------- DF 24CT 5.5 ± 0.3 21.4 ± 1.9 241.2 ± 32.8 Medium 25CT 12.6 ± 0.5 8.0 ± 1.2 98.6 ± 10.6 DF S-10
S-11
Figure S7. Relaxation mechanism of the charge transfer (CT) state of each -ortho emitter, a) 26CT, b) 23CT, c) 24CT and d) 25CT at room temperature in zeonex (1% wt) with a time delay (TD) between 1 and 100 ns. This shows that the shape of emission remains the same, meaning only one state is participating in the decay. S-12
Figure S8. Normalised phosphorescence spectra of Carbazole (Cz) and 26CT in zeonex at 80 K showing a good overlap between the two. In this case, it is possible to conclude that the PH of 26CT comes from local excited triplet state ( 3 LE) of one of the Cz donors. S-13
Figure S9. Power dependence of each emitter in zeonex at room temperature. Emission was collected at each delayed fluorescence region: a) 26CT (131 to 19889 ns); b) 23CT (141 to 9062.9 ns); c) 24CT (163 to 83942 ns); d) 25CT (215 to 50449.25 ns); e) 34CT (1.5 to 4.4 ms); f) 35CT (0.0028 to 4.5 ms). S-14
Figure S10. Energy diagram of the optimised device structure: ITO (120 nm)/ PEDOT:PSS (60 nm)/ TAPC (20 nm)/ mcp (10 nm)/ DPEPO:TADF dopant (25 nm, 30 wt%)/ TSPO1 (5 nm)/ TPBi (20 nm)/ LiF (1.5 nm)/ Al (200 nm) S-15
Figure S11. CT emission and phosphorescence (PH) spectra of a) 23CT and b) 24CT isomers from the fast and medium DF groups, respectively in a DPEPO matrix (10% volume emitter). The spectra were collected at 80 K and different time delays (TD). The onset of each spectrum resulted in an energy gap that correlates with the gaps obtained for the zeonex matrix (figure 6). Normalised Intensity (a.u.) 1.2 a) 23CT 1 CT = 2.89 +/- 0.02 ev 1.0 3 LE = 2.87 +/- 0.02 ev 0.8 0.6 0.4 0.2 TD = 25 ms E ST = - 0.02 +/- 0.02 ev 400 450 500 550 600 650 Wavelength (nm) Normalised Intensity (a.u.) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 b) 24CT TD = 25 ms 400 450 500 550 600 650 Wavelength (nm) 1 CT = 2.94 +/- 0.02 ev 3 LE = 2.82 +/- 0.02 ev E ST = 0.12 +/- 0.02 ev S-16
Figure S12. Current efficiency (a) and Luminous efficacy (b) of devices containing 23CT, 24CT and 34CT from the fast, medium and slow DF, respectively. References: (1) Dias, F. B.; Penfold, T. J.; Monkman, A. P. Photophysics of Thermally Activated Delayed Fluorescence Molecules. Methods Appl Fluoresc 2017, 5 (1), 012001. S-17