Enhancement of Luminescence Efficiencies by Thermal Rearrangement from ortho‐ to meta‐Carborane in Bis‐Carborane‐Substituted Acenes

Abstract

In a previous study we synthesized a series of bis‐o‐carborane‐modified acenes and revealed various unique luminescence properties, such as highly efficient solid‐state emission and luminochromism. Here we report further enhancement of the luminescence efficiencies of bis‐o‐carborane‐modified acenes by thermally induced structural rearrangement from ortho‐ to meta‐carborane. We found that the thermal rearrangement of the anthracene derivative 1 occurred close to the melting point and gave luminescent products. From a detailed investigation of the product obtained from 1, the transformation of the molecular structure was proven by X‐ray crystallography. In addition, the analytical data indicated that rearrangement caused by heating at 300 °C occurred at only one of the two o‐carborane units. In accord with the results of theoretical investigations of the transition states of 1 by quantum chemical calculations, we propose that the thermal rearrangement could proceed because of a low activation energy in the first rearrangement step due to the presence of the anthracene. On the basis of optical measurements, enhancements of not only luminescence efficiencies but also aggregation‐induced emission were observed. Furthermore, we have demonstrated that this strategy for enhancing emission properties is applicable ot the corresponding tetracene derivative, resulting in a deep‐red luminescent dye.