Tetrasubstituted adamantane derivatives with arylamine groups: Solution-processable hole-transporting and host materials with high triplet energy and good thermal stability for organic light-emitting devices

Four new host/hole-transporting materials, namely 4,4',4 '',4'''-(adamantane-1,3,5,7-tetrayl)tetrakis(N,N- diphenylaniline) (4TPA-Ad, 1), 4,4',4 '',4'''-(adamantane-1,3,5,7-tetrayl)tetrakis(N,N-di-p-tolylaniline) (4MTPA-Ad, 2), 1,3,5,7-tetrakis(4-(9H-carbazol-9-yl)phenyl)adamantane (4Cz-Ad, 3) and 1,3,5,7-tetrakis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl) phenyl)adamantane (4tBuCz-Ad, 4), were designed and synthesized by incorporating four electron-donating arylamine units into the rigid adamantane skeleton via a simple C-N coupling reaction. Their thermal, photophysical and electrochemical properties were investigated. The molecular design endows the materials with high triplet energies of similar to 3.0 eV, good solution processability, high thermal stability and appropriate HOMO levels. Two types of electroluminescent devices using 1-4 as hole-transporting or host materials were fabricated. The device based on 2 as solution-processed hole-transporting material and tris(quinolin-8-yloxy)aluminum as an emitter revealed a maximum current efficiency of 4.2 cd A(-1), which was comparable with the TAPC-based control device. The sky-blue device employing 2 as solution-processed host material and 4,6-(difluorophenyl)pyridine-N, C-2')picolinate (FIrpic) as an emitter showed a maximum current efficiency of 16.6 cd A(-1) with Commission Internationale de I'Eclairage (CIE) coordinates of (0.16, 0.32). (C) 2015 Elsevier B.V. All rights reserved.