Revealing the Origin of Fast Delayed Fluorescence in a Donor Functionalized Bisterpyridine.

A new carbazole-substituted bisterpyridine with pronounced delayed fluorescence is presented. While the molecular donor-acceptor-donor design suggests the origin of this to be thermally activated delayed fluorescence (TADF), results from various photophysical characterizations, OLED characteristics, temperature-dependent NMR spectroscopy, and DFT calculations all point against the involvement of triplet states. The molecule exhibits blue emission at about 440 nm with two or more fast decay channels in the lower nanosecond range in both solution and thin films.