One-Shot Synthesis of Expanded Heterohelicene Exhibiting Narrowband Thermally Activated Delayed Fluorescence

An expanded heterohelicene consisting of three BN2-embedded [4]helicene subunits (V-DABNA-Mes) has been synthesized by one-shot triple borylation. The key to success is the excessive use of boron tribromide in an autoclave. Based on the multiple resonance effect of three boron and six nitrogen atoms, V-DABNA-Mes exhibited a narrowband sky-blue thermally activated delayed fluorescence with a full width at half-maximum of 16 nm. The resonating it-extension minimized the singlet-triplet energy gap and enabled rapid reverse intersystem crossing with a rate constant of 4.4 x 10(5) s(-1). The solution-processed organic light-emitting diode device, employed as an emitter, exhibited a narrowband emission at 480 nm with a high external quantum efficiency of 22.9%.

Automated summary

An expanded heterohelicene consisting of three BN2-embedded [4]helicene subunits has been successfully synthesized through one-shot triple borylation, resulting in a narrowband sky-blue thermally activated delayed fluorescence. The resonance effect of three boron and six nitrogen atoms minimized the singlet-triplet energy gap, enabling rapid reverse intersystem crossing with a high rate constant. The organic light-emitting diode device, used as an emitter, displayed a narrowband emission with a high external quantum efficiency.