Pyridyl Pyrrolide Boron Complexes: The Facile Generation of Thermally Activated Delayed Fluorescence and Preparation of Organic Light-Emitting Diodes

The electron positive boron atom usually does not contribute to the frontier orbitals for several lower-lying electronic transitions, and thus is ideal to serve as a hub for the spiro linker of light-emitting molecules, such that the electron donor (HOMO) and acceptor (LUMO) moieties can be spatially separated with orthogonal orientation. On this basis, we prepared a series of novel boron complexes bearing electron deficient pyridyl pyrrolide and electron donating phenylcarbazolyl fragments or triphenylamine. The new boron complexes show strong solvent-polarity dependent charge-transfer emission accompanied by a small, non-negligible normal emission. The slim orbital overlap between HOMO and LUMO and hence the lack of electron correlation lead to a significant reduction of the energy gap between the lowest lying singlet and triplet excited states (ΔE_T-S) and thereby the generation of thermally activated delay fluorescence (TADF).