Phenyl‐triggered photophysical switching between normal fluorescence and delayed fluorescence in phthalonitrile‐based luminophores
In Seob Park, Hyukgi Min, Takuma Yasuda
Abstract
Abstract Herein, a facile strategy for switching luminescent properties between normal fluorescence and thermally activated delayed fluorescence (TADF) is presented. Two luminophoric molecules, VPN‐Ph and VPN‐H, combining phthalonitrile as an electron‐accepting core and triphenylamines as electron‐donating peripheries with and without two phenyl groups, are newly developed. A comparative study on their structural and photophysical properties is conducted. While non‐phenyl VPN‐H does not exhibit TADF but normal fluorescence, phenyl‐introduced VPN‐Ph exhibits TADF with a high photoluminescence quantum yield as a consequence of the phenyl‐triggered steric congestion. By virtue of the TADF feature, an organic light‐emitting diode (OLED) incorporating VPN‐Ph as an emitter achieves a maximum external electroluminescence (EL) quantum efficiency as high as 28.0%, which is five times higher than that of the VPN‐H‐based OLED. Thus, phenyl‐triggered geometric modulation has a drastic impact on the resulting photophysical and EL properties, leading to TADF on/off switching.