Molecular Engineering through Control of Structural Deformation for Highly Efficient Ultralong Organic Phosphorescence

It is an enormous challenge to achieve highly efficient organic room-temperature phosphorescence (RTP) with a long lifetime. We demonstrate that, by bridging the carbazole and halogenated phenyl ring with a methylene linker, RTP phosphors CzBX (X=Cl, Br) present high phosphorescence efficiency (phi(Ph)). A phi(Ph) up to 38 % was obtained for CzBBr with a lifetime of 220 ms, which is much higher than that of compounds CzPX (X=Cl, Br) with a C-N bond as a linker (phi(Ph)<1 %). Single-crystal analysis and theoretical calculations revealed that, in the crystal phase, intermolecular pi-Br interactions accelerate the intersystem crossing process, while tetrahedron-like structures induced by sp(3) methylene linkers restrain the nonradiative decay channel, leading to the high phosphorescence efficiency in CzBBr. This research paves a new road toward highly efficient and long-lived RTP materials with potential applications in anti-counterfeiting or data encryption.