The First Tandem, All-exciplex-based WOLED

Transcription

1 The First Tandem, All-exciplex-based WOLED Wen-Yi Hung* 1, Guan-Cheng Fang 1, Shih-Wei Lin 2, Shuo-Hsien Cheng 2, Ken-Tsung Wong* 2,3, Ting-Yi Kuo, Pi-Tai Chou* 2,4 1 Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, 20224, Taiwan. wenhung@mail.ntou.edu.tw 2 Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan. chop@ntu.edu.tw;kenwong@ntu.edu.tw 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan. 4 Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei, 10617, Taiwan Supporting Information Synthesis: The triazine core (1) was synthesized by the triflic acid-promoted condensation of 3-iodobenzonitrile. The palladium-catalyzed C-P bond formation converted 1 to the diphenylphosphine-substituted intermediate 2, which was subsequently oxidized by hydrogen peroxide to afford PO-T2T in excellent yield. All intermediates and PO-T2T were analyzed with satisfactory data (see experimental section in ESI) to verify the purity. Reagents and conditions for the synthesis of PO-T2T. i, CF 3 SO 3 H, anhydrous CH 2 Cl 2, 0 o C, 73%. ii, HPPh 2, Pd(PPh 3 ) 4, NEt 3, anhydrous toluene, 80 o C, 50%. iii, 30% H 2 O 2, anhydrous CH 2 Cl 2, rt., 98%.S- Tris(3-iodophenyl)triazine (1). Trifluoromethane sulfonic acid (11.6 ml, 131 mmol) was added to S- 1

2 a solution of 3-iodobenzonitrile (15.0 g, 65.5 mmol) in CH 2 Cl 2 (130 ml). The mixture was stirred at room temperature for 12 h and then quenched with saturated NaHCO 3(aq). The aqueous phase was extracted with CH 2 Cl 2, dried with MgSO 4. After removing the solvents, the resulting solid was washed with pentane to give a white solid (10.9 g, 73%). Mp 261~262 o C;IR (KBr) ν 3057, 1610, 1572, 1519, 1415, 1352, 1264, 1147, 1059, 992, 902, 864, 839, 777, 725, 675, H NMR (CDCl 3, 400 MHz) δ 9.02 (s, 3 H), 8.70 (d, J = 8.0 Hz, 3 H), 7.96 (d, J = 7.6 Hz, 3 H), 7.33 (t, J = 8.0 Hz, 3 H). 13 C NMR (CDCl 3, 100 MHz) δ 17, 141.7, 137.8, 137.7, 13, 128.3, HRMS (m/z, ESI + ) Cacld. for C 21 H 12 I 3 N , found ([M+H] + ). Tris(3-(diphenylphosphino)phenyl)triazine (2). A mixture of triazine 1 (1 g, 14.6 mmol), diphenylphosphine (8.40 ml, 48.3 mmol), Pd(PPh 3 ) 4 (0.50 g, 3 mmol), and triethylamine (6.60 ml, 48.2 mmol) in toluene (120 ml) was heated at 80 o C for 24 h under argon. After cooling to room temperature, the reaction was quenched with water and then extracted with CH 2 Cl 2. The combined organic solution was dried over MgSO 4 and concentrated under rotary evaporation. The resulting solid residue was purified on silica gel column chromatography with 9:1 (v/v) EtOAc/hexanes as the eluent and reprecipitated from CH 2 Cl 2 /methanol to afford a white solid (6.3 g, 50%). Mp 219~220 o C;IR (KBr) ν 3052, 1578, 1519, 1476, 1433, 1416, 1351, 1267, 1173, 1092, 1027, 997, 916, 883, 846, 791, 742, 693, 642, H NMR (CDCl 3, 400 MHz) δ 8.57 (d, J = 7.0 Hz, 3 H), 8.49 (d, J = 7.8 Hz, 3 H), (m, 6 H), (m, 30 H). 13 C NMR (CDCl 3, 100 MHz) δ 171.3, 138.1, 138.0, 137.9, 137.7, 136.9, 136.8, 136.2, 136.1, 134.2, 134.0, 133.9, 133.7, 129.4, 128.9, 128.8, 128.7, P NMR (CDCl 3, 400 MHz) δ HRMS (m/z, ESI + ) Cacld. for C 57 H 42 N 3 P , found ([M+H] + ). PO-T2T. To a solution of 2 (1.50 g, 1.74 mmol) in distilled CH 2 Cl 2 (10 ml), which was treated with P 2 O 5, 30% H 2 O 2(aq) (1.30 ml, 13.0 mmol), was slowly added and stirred for 12 h under room temperature. The mixture was quenched with water and then extracted with CH 2 Cl 2. The combined organic solution was dried over MgSO 4 and concentrated under rotary evaporation. The solid residue was reprecipitated from CH 2 Cl 2 /hexanes to afford a white solid (1.55 g, 98%). Mp 287 o C (DSC);IR (KBr) ν 3052, 1635, 1593, 1523, 1436, 1356, 1274, 1198, 1115, 996, 922, 891, 796, 751, 723, 694, 641, H NMR (CDCl 3, 400 MHz) δ 8.99 (d, J = 12.4 Hz, 3 H), 8.73 (d, J = 7.6 Hz, 3 H), (m, 3 H), (m, 12 H), (m, 3 H), (m, 18 H). 13 C NMR (CDCl 3, 100 MHz) δ 170.9, 136.1, 136.0, 135.9, 133.9, 132.8, 132.7, 132.5, 132.4, 132.2, 132.1, 131.7, 129.0, 128.9, 128.7, P NMR (CDCl 3, 400 MHz) δ HRMS (m/z, FAB + ) Cacld. for C 57 H 42 N 3 O 3 P , found Anal. Calcd. C, 75.24;H, 4.65;N, 4.62, found C, 75.48; H, 4.36;N, Experimental Section S- 2

3 Photophysical measurements: Steady-state absorption and emission measurements in solution and film were recorded with a Hitachi (U-3310) spectrophotometer and an Edinburgh (FS920) fluorometer, respectively. Both the wavelength-dependent excitation and emission response of the fluorometer have been calibrated. Nanosecond lifetime studies were performed with an Edinburgh FL 900 photon-counting system using a hydrogen-filled lamp as the excitation source. The emission decays were fitted by the sum of exponential functions with a temporal resolution of ~300 ps via the deconvolution of instrument response function. Ultrafast time-resolved studies were performed by a femtosecond fluorescence up-conversion system (FOG100, CDP), in which a rotating sample cell was pumped by second harmonic generation (SHG, at 380 nm) of a pulse-selected fundamental laser pulses at 760 nm (~ 100 fs in duration). The resulting fluorescence was collected, focused, and frequency summed in a BBO crystal along with an interrogation gate pulse (760 nm) at a designated delay time with respect to the pump pulse. A λ/2 waveplate was used to set the polarization between pump and gate pulses at a magic angle of 54.7 o to prevent fluorescence anisotropy contributed by solute reorientation. Fluorescence up-conversion data were fitted to the sum of exponential functions convoluted with the instrument response function, which was determined by measuring the Raman scattering signal. The system response time is about 120 fs. Time-of-flight (TOF) mobility measurements: Carrier-transport properties were studied by the time-of-flight (TOF) transient photocurrent technique. For PO-T2T compound, we used terfluorene (E3) as the charge-generation layer (CGL) in the structure: ITO glass/ E3( µm)/ PO-T2T (2.1 µm) /Ag (200 nm), which were then placed inside a cryostat and kept under vacuum. The thicknesses of organic materials under testing were still set to be substantially greater than that of E3, so that the total transit time was longer than the time resolution of the electronic system. Accordingly, the transit time across the E3 layer is negligible in comparison with the total transit time. The thickness of organic film was monitored in situ with a quartz sensor and calibrated by a thin film thickness measurement (K-MAC ST2000). A pulsed nitrogen laser (337 nm) was used as the excitation light source through the transparent electrode (ITO) inducing photogeneration of a thin sheet of excess carriers. Under an applied dc bias, the transient photocurrent was swept across the bulk of the organic film toward the collection electrode (Ag), and then recorded with a digital storage oscilloscope. Depending on the polarity of the applied bias, selected carriers (holes or electrons) are swept across the sample with a transit time of t T. With the applied bias V and the sample thickness D, the applied electric field E = V/D, and the carrier mobility is then given by µ = D/(t T E) = D 2 /(Vt T ), in which the carrier transit time, t T, can be extracted from the intersection of two asymptotes to the tail and plateau sections in the double-logarithmic plots. OLED device fabrications: All chemicals were purified through vacuum sublimation prior to use. The OLEDs were fabricated through vacuum deposition of the materials at 10 6 Torr onto the S- 3

4 ITO-coated glass substrates having a sheet resistance of 15 Ω sq 1. The ITO surface was cleaned ultrasonically; i.e. with acetone, methanol, and deionized water in sequence and finally with UV-ozone. The deposition rate of each organic material was ca. 1 2 Å s 1. Subsequently, Liq was deposited at 0.1 Å s 1 and then capped with Al (ca. 5 Å s 1 ) through shadow masking without breaking the vacuum. The J V L characteristics of the devices were measured simultaneously in a glove-box using a Keithley 6430 source meter and a Keithley 6487 picoammeter equipped with a calibration Si-photodiode. EL spectra were measured using a photodiode array (Ocean Optics USB2000). S- 4

5 Supplementary Table Table S1 Physical properties of PO-T2T T g /T c /T m a ( o C) T d b ( o C) λ abs (nm) c λ PL (nm) c d E g sol. film sol. film (ev) E T e (ev) E 1/2 Red f (V) HOMO/LUMO g (ev) PO-T2T n.d. h /192/ n.d. h /-2.83 a Determined by DSC measurement. b Calculated from TGA result (5% weight loss). c The solution spectra were probed in CH 2 Cl 2. d Calculated from the absorption onset of the solution spectrum. e Probed in 2-MeTHF. f The reduction potential was probed in THF solution containing 0.1 M TBAP and was referred to the Fc/F C + redox couple. g LUMO level was calculated from reduction potential as referred to the HOMO of ferrocene. HOMO = LUMO - E g. h Not detected. Supplementary Figures E T =2.99eV PO-T2T Film solution Phos Figure S1. Room-temperature absorption and photoluminescence (PL) spectra of POT2T in CH 2 Cl 2 solution and thin film as well as corresponding phosphorescence (Phos) spectra recorded in EtOH solution at 77 K. S- 5

6 4 2 PO- T2T I(m A ) Potential(V vs Fc/Fc + ) Figure S2. Cyclic voltammogram of PO-T2T in THF containing 0.1 M TBAPF 6 as supporting electrolyte. A glassy carbon, Pt wire and Ag/AgCl were used as working, counter and reference electrodes, respectively. a Photocurrent (µa) 150 PO-T2T (e) E=8.6X10 5 V/cm ( ) ( ) Time (µsec) µ (cm 2 / V s) 5E-3 4E-3 PO-T2T 3E-3 2E-3 1E E 1/2 (V/cm) 1/2 Figure S3. (a) Representative TOF transient photocurrent signals for electrons of PO-T2T at E= V cm 1 and insets are the double logarithmic plots. (b) Electron mobility of PO-T2T plotted with respect to E 1/2. b. S- 6

7 Figure S4. Energy level diagram of the devices fabricated in this study. (a) TCTA ev (b) DTAF ev (c) TAPC ev (d) NPNPB ev Figure S5. HOMO energy level determined by using photoelectron yield spectroscopy (AC-2): (a)tcta, (b) DTAF, (c)tapc and (d) NPNPB. S- 7

8 a mcp UV-Vis PL b TCTA UV-Vis PL c DTAF UV-Vis PL d TAPC UV-Vis PL e NPNPB UV-Vis PL Figure S6. Room-temperature absorption and emission (PL) spectra of donors in thin film: (a) mcp, (b)tcta, (c) DTAF, (d)tapc and (e) NPNPB. 0 CIE coordinates Current Density (ma/cm 2 ) CIEx CIEy Figure S7. The CIE coordinates of white EL spectra as a function of the current density. S- 8

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