Efficient up-conversion process by isolation of two chromophores in thermally activated delayed fluorescent emitters

Two thermally activated delayed fluorescent (TADF) emitters built on the design approach isolating two TADF chromophores were developed by coupling them through a meta- functionalized phenyl linker. The rate constant of reverse intersystem crossing (RISC) was improved by the chromophore isolation method via a reduced singlet–triplet energy gap and the photoluminescence quantum yield was enhanced by the two independent TADF emitting units. The external quantum efficiency of the TADF emitters was over 20%, which was much higher than that of the previously reported TADF emitter (13.5%) by electronically separating the two TADF chromophores. This work demonstrated that the newly proposed design can increase the EQE and facilitate RISC process by electronic separation of the two TADF units via the meta functionalized phenyl linker.