4-Diphenylaminocarbazole: Switching Substituent Position for Voltage Reduction and Efficiency Enhancement of OLEDs

Abstract

Simple but exceptionally efficient 4-diphenylaminocarbazole host material, 4-DPACz, is presented and compared with its positional isomer, 1-DPACz. The shift of diphenylamino substituent from the 1-position to 4-position of carbazole resulted in an increase in the HOMO energy level as well as an increase in triplet energy level. Having a high triplet energy level (2.76 eV) and well-matched HOMO energy level (-5.61 eV), 4-DPACz showed reduced driving voltage and higher efficiencies for solution-processed green PhOLEDs compated to PVK as well as 1-DPACz. Maximum luminous, power, and external quantum efficiencies reaching to 47.9 cd A, 25.2 lm W, and 14.3%, respectively, were achieved with a device configuration of [ITO/PEDOT:PSS/4-DPACz:Ir(mppy)/TPBi/CsF/Al]. Additional enhancement of efficiencies of 4-DPACz was verified when incorporating another dopant, Ir(Si-bppy)(acac), resulting in 59.1 cd A, 29.5 lm W, and 15.8%. Furthermore, reduced efficiency roll-off was clearly observed for 4-DPACz compared with PVK. Such improved device characteristics of 4-DPACz were attributed to its high hole mobility and charge balance inside the emitting layer therof. The excellent results using such a simple-structured 4-DPACz could promote various applications of this 4-DPACz unit as a building block structure for further possible oligomeric, dendritic, and polymeric materials.

Tuning Intramolecular Conformation and Packing Mode of Host Materials through Noncovalent Interactions for High-Efficiency Blue Electrophosphorescence

“…The absorption spectra of PyDCz , PymDCz , and PyaDCz are quite similar in both solution and film states, revealing two strong absorption band peaked at ∼290 and ∼340 nm, which could be ascribed to the π–π* and n−π* transitions of carbazole moiety, respectively. 24,25 For the PL spectra, PyDCz , PymDCz , and PyaDCz show broad and structureless emission peaks (λ max ) at 382, 431, and 445 nm in DCM solution, respectively, indicating their intramolecular charge transfer (ICT) emission features due to the CT from the electron donating carbazole unit to highly electron-deficient nitrogen heterocyclic ring. 26 The characteristics of ICT emissions were further verified by the emission profiles in the different solvents with variated polarities.…”

Short Syntheses of 1-Substituted Dibenzothiophenes and 3-Substituted Naphthothiophenes

“…No 1-iododibenzothiophene sublimed under these conditions. 1 H NMR (500 MHz, CDCl3): δ 9.41-9.39 (m, 1H), 8.03 (d, J= 7.6 Hz, 1H), 7.88-7.86 (m, 2H), 7.57-7.52 (m, 2H), 7.10 (m, 1H). 13 1-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan2-yl)dibenzothiophene (3e): To the above prepared solution of 1-lithiodibenzothiophene was added iPrOB(pin) (3.2 mL, 15.7 mmol, 2 equiv) was added.…”

“…An attempt to filter a highly concentrated ethereal solution of bromide 12d through basic alumina did result in darkening and exothermic decomposition, indicating this compound should be treated cautiously. 1…”

“…The aqueous layer washed with an ad-ditional 25 mL dichloromethane, and the combined residues were dried over Na2SO4 and concentrated. The brown residue was purified by flash chromatography (5%-10% ethyl acetate/hexanes) to afford aldehyde 9c as a orange/yellow solid (749 mg, 3.52 mmol, 58% yield) 1 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan2-yl)naphthothiophene (9d): In a recovery flask, 3-bromoaphthothiophene (500 mg, 1.9 mmol, 1 equiv) was dissolved in 3 mL THF. Separately 6 mL of THF was placed in a Schlenk flask and cooled to -84 °C (liquid nitrogen/ethyl acetate).…”

“…Isomeric arenes can confer dramatically different properties on molecules that contain them. 1,2 Introduction of heteroatoms such as sulfur into polycyclic aromatic hydrocarbons further changes their properties relative to the parent hydrocarbons, and chemistry to access sulfur-containing polycyclic aromatic hydrocarbons has been an area of substantial study. 3…”