Novel electron acceptor based on spiro[fluorine-9,9′-xanthene] for exciplex thermally activated delayed fluorescence

Two cyano-substituted spiro[fluorine-9,9′-xanthene] (SFX) derivatives, 2-carbonitrile-spiro[fluorene-9,9′-xanthene] (CNSFX) and 2,7-dicarbonitrile-spiro[fluorene-9,9′-xanthene] (DCNSFX) were conveniently prepared as electron acceptors to combine with tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as electron donor to form exciplex emitters, respectively. Favorable exciplex-TADF was successfully achieved with photoluminescence quantum yield of 31% and electroluminescence efficiency of 8.2 cd A⁻¹ in TCTA:DCNSFX, which possesses increases of 1.1 and 3.3 times than those (15% and 1.9 cd A⁻¹) of TCTA:CNSFX, respectively. The relatively favorable performance of TCTA:DCNSFX is related to the stronger electron-accepting ability through dicyano-substitution and larger driving force in the exciplex emission. These appealing results reveal that the dicyano-substituted SFX derivative opens interesting perspectives for developing favorable exciplex-TADF organic light-emitting diodes in the future.