Novel boron- and sulfur-doped polycyclic aromatic hydrocarbon as multiple resonance emitter for ultrapure blue thermally activated delayed fluorescence polymers

Boron (B)- and sulfur (S)-doped polycyclic aromatic hydrocarbons (PAHs) are developed as a novel kind of multiple resonance emitters for ultrapure blue thermally activated delayed fluorescence (TADF) polymers with narrowband electroluminescence. The combination of electron-deficient B atom and electron-rich S atom in PAH can form an intramolecular push-pull electronic system in a rigid aromatic framework, leading to reduced singlet-triplet energy splitting and limited structure relaxation of excited states. The critical roles of S atom in determining emission properties with respect to the oxygen analogues are in two aspects: (i) reducing energy bandgap to shift emission from human-eye-insensitive ultraviolet zone to blue region, and (ii) promoting reverse intersystem crossing process by heavy-atom effect to activate TADF effect. The resulting polymer containing B,S-doped PAH as emitter and acridan as host exhibits efficient blue electroluminescence at 458 nm with small full-width at half-maximum of 31 nm, representing the first example for ultrapure TADF polymer with narrowband electroluminescence.

Automated summary

The combination of boron and sulfur-doped polycyclic aromatic hydrocarbons forms an intramolecular push-pull electronic system in rigid aromatic frameworks, which plays a critical role in reducing energy splitting and excited state relaxation, leading to efficient blue electroluminescence with narrowband emission in polymers. The sulfur atom in determining emission properties by reducing energy bandgap and promoting TADF effect through heavy-atom effect.