A computational study of tri-s-triazine-based molecules as ambipolar host materials for phosphorescent blue emitters: effective geometric and electronic tuning

Abstract

A series of host molecules for blue electrophosphorescence have been designed using density functional theory by incorporating carbazole and tri-s-triazine. It is found that the carbazole ring should be coplanar with a tri-s-triazine ring for obtaining high triplet energy (E_T). Results obtained from the electronic structure calculations show that the triplet energy, HOMO and LUMO energy levels and reorganization energy (λ) of the designed hosts can be modulated efficiently through different substitution patterns. This study provides theoretical insights into the nature of host molecules, and shows that the designed molecules with an NH₂ group in a tri-s-triazine ring and an alkyl group in a carbazole ring can meet the requirements of the host materials for blue emitting phOLEDs owing to their high E_T value, appropriate energy level alignment, balanced charge transfer, high triplet exciton-formation fraction (χ_T) and small difference between S₁ and T₁ excitation energy (ΔE_ST).