Rational design of carbazolyl and aryl phosphine oxide (APO) based ambipolar host materials for blue electrophosphorescence: a density functional theory study

Abstract

We have designed 10 host molecules for blue/green electrophosphorescence by combining the electron donor carbazolyl unit and the electron acceptor aryl phosphine oxide unit into a single molecular unit by density functional theory. In addition, we have systematically investigated the influence of the phenyl spacers, phenyl substitution and the type of bridge (diphenylether-bridge or diphenylamine-bridge) on an array of electronic properties of the designed ambipolar hosts. For all designed host molecules, host molecule 5 in which the phenyl ring with carbazolyl and phenyl substituted at the o-position was directly combined with phosphine oxide through a diphenylether-bridge linkage could retain a high triplet energy and showed great potential for blue phosphorescent organic light-emitting diodes. Furthermore, the Förster and Dexter energy transfer mechanisms between all designed host molecules and guests are thermodynamically feasible. In addition, we built a host–guest model to investigate the charge transfer mechanism, and the results indicate that a good intermolecular charge transfer can be attained between host and guest materials.