Room-temperature phosphorescence (RTP) materials have been pursued by academics owing to their full utilization of excited state energy and long lifetimes, which show potential applications in displays, encryption, anti-counterfeiting, sensors and bioimaging. However, it is an enormous challenge to realize efficient RTP in pure organic molecules due to the inefficient intersystem crossing (ISC) caused by weak spin orbit coupling (SOC) and the fast deactivation pathways of triplet excitons.

To address the above issue, Prof. Zhu Weiguo (Changzhou University) and Prof. An Zhongfu (Nanjing University of Technology) reported a novel D-C(sp³)-A RTP molecules, in which the methylene linkers was integrated into the donor and acceptor units. The sp³ methylene in these molecules has some merits: 1) creates tetrahedron-like molecular geometry, favoring formation of strong intermolecular interaction in crystal, and 2) it breaks the electron delocalization between donor and acceptor units, hampering the structural deformation in the excited state transition. Both single-crystal analysis and theoretical calculations revealed that, in the crystal phase, intermolecularπ-Br interactions accelerate the intersystem crossing process, while tetrahedron-like structures induced by sp3 methylene linkers restrain the nonradiative decay channel, leading to the high phosphorescence efficiency (38%) in CzBBr. This research paves a new road toward highly efficient and long lived RTP materials.

This research entitled ‘Molecular Engineering via Controlling Structural Deformation for Highly Efficient Ultralong Organic Phosphorescence’ was published in Angew. Chem. Int. Ed (2021, 60, 2058–2063). Changzhou University is the first institution. Yin Zheng and Gu Mingxing are the co-first authors. Prof. Wang Yafei, Prof. Zhu Weiguo and Prof. An Zhongfu are the corresponding authors. In addition, associated Prof. Ma Huili (Nanjing University of Technology) gave great support in theoretical calculation in this research work.

Original Paper Links: https://doi.org/10.1002/anie.202011830