Indication of Intramolecular Triplet–Triplet Annihilation Upconversion in Organic Light-Emitting Diodes

Abstract

It is well known that triplet–triplet annihilation upconversion (TTU) can enhance electroluminescence (EL) efficiency by converting two low-energy triplet excitons into one high-energy singlet exciton. However, conventional intermolecular TTU requires high doping concentration to activate, limiting device architecture. Here, six dimer molecules comprised of two anthracene units connected by a spacer unit are investigated, which have a possibility of the intramolecular TTU process. As a result, two dimer molecules show high TTU efficiencies close to the theoretical maximum even in dispersed, diluted conditions. By comparing these molecular conformations, a correlation is found between the dimer structures of two anthracene units and the TTU activity in the diluted condition, i.e., the 3D molecular structure with the exciton utilizing efficiency.