Although carborane-based luminescent materials have been studied for years, no persistent phosphor has been reported so far. Herein, we describe boron-cluster-based persistent phosphors obtained by linking a σ-aromatic carboranyl cage to the π system of a carbazolyl group. The carboranes were found to promote intersystem crossing from a singlet to a triplet state. The rigid boron cluster was able to stabilize the ultralong triplet excitons through multiple nonclassical hydrogen bonds, such as B-H⋅⋅⋅π interactions, thus leading to a long lifetime of up to 0.666 s and an absolute phosphorescence quantum yield of 7.1 %, which is outstanding for an organic phosphor without heavy atoms. These phosphors can be excited by visible light and show dynamic emission behavior, including thermochromism and mechanochromism. This study demonstrates that non-metal/heavy-atom boron clusters can be used to develop multifunctional high-performance phosphors for potential applications.
Keywords: carboranes; intersystem crossing; nonclassical hydrogen bonds; persistent phosphors; phosphorescence.
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.