A simple construction of multiple highly-efficient orange-emitting carboranes based on interlocked molecular aggregations

Abstract

Convenient approaches or precursors for the preparation of multiple orange-to-red emitting materials are still lacking. Carborane is an electron-withdrawing carbon–boron cluster (via a C-connection) that exhibits great potential for aggregation-induced emission (AIE) and a natural advantage for orange-to-red photoluminescence (PL). However, the current orange-to-red emitting carboranes suffer from several drawbacks, which limit the further applications. In this work, a triphenylaminyl/carbazolyl carborane triad bearing a reactive N–H moiety was designed as a precursor with strong orange AIE and the efficiency was high as 0.90 in the solid state. This triad could be derived by efficient nucleophilic substitutions and C–N cross couplings, affording multiple orange-emitting carboranes with efficiencies varying from 0.94 to 0.99. The crystallographic studies showed typical interlocked molecular aggregations in the solid state, and the substituents of these carboranes were well confined due to the short-ranged π⋯π and H⋯H (or F) interactions, forming highly-rigid aggregates. Single-molecule calculations show the twisted intramolecular charge-transfer (TICT) excited state in the free state, whereas the ONIOM modelling showed a decrease in the vibrations of the substituents and an increase in the oscillator strength in the TICT electronic transition in the solid state.