Supporting Information

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1 Supporting Information A New Molecular Design Based on Thermally Activated Delayed Fluorescence for Highly Efficient Organic Light Emitting Diodes Pachaiyappan Rajamalli, Natarajan Senthilkumar, Parthasarathy Gandeepan, Pei-Yun Huang, Min-Jie Huang, Chen-Zheng Ren-Wu, Chi-Yu Yang, Ming-Jui Chiu, Li-Kang Chu, Hao-Wu Lin and Chien-Hong Cheng * Department of Chemistry, National Tsing Hua University, Hsinchu 3003, Taiwan. chcheng@mx.nthu.edu.tw Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 3003, Taiwan. General Information The H and 3 C NMR spectra were recorded using Varian mercury 400 spectrometer. The HRMS were measured using MAT-95XL HRMS. The decomposition temperature was determined by TGA using TG/DTA Seiko SSC-5200 instrument and glass transition temperature was determined by DSC under nitrogen atmosphere on a DSC-Q0 instrument. UV-visible absorption spectra were measured using a Hitachi U-3300 spectrophotometer. Fluorescence and phosphorescence spectra were recorded on a Hitachi F-7000 spectrophotometer. Transient PL measurement of the materials in solution were obtained using 355 nm pulsed laser (Nd:YAG laser, INDI-40-0, Spectra-Physics) as the excitation source and the sample was excited by the optical fiber (77532, Newport Corp). A highpass filter (GG , Lamd at 40 nm in front of the photodiode (DET0A/M, Thorlabs) was used to prevent the scattering of 355-nm laser. The electronic signal was recorded by an oscilloscope (WaveSurfer 24MXs-B, LeCroy). The temperature-dependent transient photoluminescence was measured in a vacuum cryostat (Janis Research). A Nd:YAG pulsed laser (λ = 355 nm, pulse width 0 ns, repetition rate = 0 Hz) S

2 was used as an excitation source. The emission from the sample was coupled by a fiber bundle to a monochromator (Princeton Instruments) equipped with a red-enhanced thermoelectric cooling photomultiplier (Becker & Hickl). Photon counting was performed by a multi-channel scaling single photon counting system (Becker & Hickl). The absolute PL quantum efficiency of the doped films were determined using an integrating sphere under N 2 atmosphere. The electrochemical properties of these benzoylpyridine derivatives were measured by CH Instruments 600A electrochemical analyzer. The oxidation measurements were measured using glassy carbon electrode as the working electrode, an Ag/Ag + ( M AgNO 3 ) as the reference electrode and Pt wire as the counter electrode, respectively in dichloromethane. The HOMO energy level were determined from the onset of the oxidation potential using the equation -(4.8 ev + E ox (vs Fc ox )). DFT Calculation Molecular geometry optimizations and electronic properties were carried out by the Gaussian 03 program with density functional theory (DFT) and time-dependent DFT (TDDFT) calculations in which the Becke s three parameter functional combined with Lee, Yang, and Parr s correlation functional (B3LYP) hybrid exchange-correlation functional with the 6-3G* basic set were used. The molecular orbitals were visualized using Gaussview 4. software. OLEDs Fabrication and Measurement Organic materials used in device fabrication were usually purified by sublimation. Device were fabricated by vacuum deposition onto pre-coated ITO glass with sheet resistance of 25 Ω/square at a pressure lower than 0-6 Torr. Organic materials were deposited at the rate of 0.5~.2 Å s -. LiF and Al were deposited at the rate of 0. Å s -, 3-0 Å s -, respectively. Rest of the procedures are similar to the reported method. 2 S2

3 Figure S. DFT optimized structure of DCBPy (, DTCBPy ( and distance between carbazole and benzoyl pyridine were measured using Gaussview 4. software. n-hexane Tol THF DCM n-hexane Tol THF DCM Absorbance Absorbance c) Hex Tol THF DCM d) n-hexane Tol THF DCM Figure S2. Absorbance spectra and fluorescence spectra of DCBPy (a and c) and DTCBPy (b and d) in various solvents at RT (0-5 M). S3

4 Table S: Comparison of calculated and experimental absorption, singlet, triplet and E ST value of DCBPy and DTCBPy Dopant λ abs (nm) (cal) λ abs (nm) (exp)a E g (Cal) E g (ev) (exp) b E T (ev) (cal) E T(exp) c E ST(cal) E ST(exp) DCBPy 326, 46 3, DTCBPy 335, , a Measured in toluene ( 0-5 M) at room temperature. b Measured in toluene ( 0-5 M) at room temperature and estimated from the onset of fluorescence spectrum. c Phosphorescence measured in toluene ( 0-5 M) at 77 K and estimated from the onset of phosphorescence spectrum. DCBPy DTCBPy Current, A Currennt, A Potential (Vs Ag/Ag + ) Potential (V vs Ag/Ag + ) Figure S3. Oxidization and reduction potentials of DCBPy ( and DTCBPy (; oxidation potentials were measured in 0-3 M DCM and reduction potentials were measured in 0-3 M THF solution. The electrode potentials were measured versus Ag/Ag + electrode. 2.0x0-5 x0-5 Cy Cy 2 Cy 3 5.0x0-6 cyc- cyc-2 cyc-9 Current, A -x x x0-5 Current, A -5.0x0-6 -x x x x x Potential, V Potential, V Figure S4. Repeated cyclic voltammograms (oxidization) for DCBPy and DTCBPy in DCM solutions. S4

5 0~0 h ~0 h Figure S5. PL spectra of the encapsulated single layers (80 nm) of DCBPy (, DTCBPy ( obtained once every one hour under continuous UV excitation (340 nm). Fl. at RT Phos. at 77 K Pl at RT Phos at 77 K c) Pl at RT phos. at 77 K Figure S6. Fluorescence and phosphorescence spectra of 5 wt% DCBPy doped in CzPS film (, 5 wt% DTCBPy doped in CBP film (, and DTCBPy single crystal (c). The Fluorescence and phosphorescence spectra were measured at 300 K and 77 K respectively. S5

6 Table S2: Photoluminescence quantum yields (PLQY) of DCBPy and DTCBPy in various solvents and thin films. Compound n-hexane a Toluene a THF a DCM a Thin film (%) b DCBPy c DTCBPy d a Quantum yield, estimated using diphenyl anthracence as the standard. b Absolute total PL quantum yield evaluated using an integrating sphere. c 5 wt% DCBPy doped in CzPS film. d 5 wt% DTCBPy doped in CBP film. 00 Weight (%) DCBPy DTCBPy Temperature, o C Figure S7. The thermogravimetric thermograms of DCBPy and DTCBPy. DCBPy DTCBPy Endothermic Tg Endothermic Tg Temperature, o C Temperature, o C Figure S8. The differential scanning calorimetry traces of ( DCBPy and ( DTCBPy. S6

7 Current efficiency, cd A Device B Device G Power efficiency, lm W - 0 Device B Device G Luminance, cd m Luminance, cd m -2 Figure S9 The current efficiency vs luminance, power efficiency vs luminance of these two devices. 6 V 8 V 0 V 2 V 6 V 8 V 0 V 2 V Figure S0. The EL spectra of devices under different voltages device G, device B. Current density, ma cm Device G V Luminance, cd m -2 E.Q.E Device G Device G Luminance, cd m -2 Figure S. The EL characteristic plots of device G: current density and luminance vs driving voltage; external quantum efficiency vs luminance and inset: electroluminescent spectrum. S7

8 Table S3: External quantum effeciency and Current efficiency of devices B, G and G at 00 cd m -2 and 000 cd m -2 Device EQE max (%) a EQE (%) b EQE (%) c Current efficiency (cd A - ) b Current efficiency (cd A - ) c B G G a EQE max, maximal external quantum efficiency, b measured at 00 cd m -2, c measured at 000 cd m -2. References ) Chen, Y.-H.; Chou, H.-H.; Su, T.-H.; Chou, P.-Y.; Wu, F.-I.; Cheng, C.-H. Chem. Commun., 20, 47, ) Lin, J.-J.; Liao, W.-S.; Huang, H.-J.; Wu, F.-I.; Cheng, C.-H. Adv. Funct. Mater. 2008, 8, 485. S8

9 H and 3 C NMR spectra N N N O S9

10 S0