Sulfur atom manipulates geometric isomerism of diphosphinine oxides for efficient delayed fluorescence diodes

Abstract Geometric isomerism has significant influences on intermolecular interactions. Therefore, despite the challenge, geometry manipulation is desired for developing high-performance optoelectronic materials. Herein, we demonstrate that heteroatom incorporation is a feasible approach to control cis- and trans- configurations of diphosphinine oxide compounds. Molecular geometries are highly dependent on heteroatom position, which is manifested by a cis- (cDPDPbDTO) and a trans- dithiophene-fused diphosphinine dioxide (tDPDPcDTO). It is showed that effects between S and P atoms bonded with the same C atoms bend the fused ring of cDPDPbDTO, giving rise to its cis-configuration. In contrast to trans-featured tDPDPcDTO containing a planar fused ring, cDPDPbDTO reveals more compact packing mode, accompanied by limited π-π stacking, and remarkably condensed excited states. Consequently, in addition to higher carrier mobility, cDPDPbDTO is much more effective in quenching suppression. Doped with a bluish green thermally activated delayed fluorescence (TADF) dye 2CzPN, cDPDPbDTO hosted film achieves fourfold increased radiative rate constant, and tenfold and sixfold decreased singlet and triplet nonradiative rate constants, respectively, as well as a 40%-improved reverse intersystem crossing (RISC) efficiency (97%). As the result, cDPDPbDTO endows its TADF systems with the state-of-the-art photoluminescence and electroluminescence quantum efficiencies of 95% and 26%, respectively.