Boosting ultralong organic phosphorescence performance by synergistic heavy-atom effect and multiple intermolecular interactions in molecular crystal

Abstract

Ultralong organic phosphorescent (UOP) luminogens are of great practical importance in the field of optoelectronics, however, it remains a significant challenge to construct materials with high phosphorescent yields (Φ_ph) and long lifetimes simultaneously. We herein present a feasible molecular engineering strategy to boost the Φ_ph and lifetime via a synergistic heavy-atom effect and methylation approach used to adjust the intrinsic photophysical processes and solid packing. As expected, efficient UOP with an enhanced Φ_ph of 11.1% and an improved lifetime of 391 ms is obtained for BrMOPP consisting of one methyl moiety and bromine atom in the S,S-dioxide phenothiazine skeleton, which is much better than that of reference luminogen without functional units (0.5%, 185 ms). Dense network packing formed through multiple intramolecular interactions along with a, b, and c axis directions provides the rigid molecular alignment in the three-dimensional framework, suppressing the nonradiative relaxation pathway. Combining with the efficient intersystem crossing induced by the bromine atom, the resulting phosphors with excellent Φ_ph and long lifetime are achieved, and are successfully applied to anti-counterfeiting and data encryption. This study will provide a reasonable approach for further optimizing the UOP performance from the molecular level.