High radiative efficiency based on intramolecular charge transfer in a 9,9′-bianthracene-ortho-carboranyl luminophore

Abstract

Herein, we prepared an o-carborane compound (9biAT) linked to a 9,9′-bianthracene moiety at each C9-position. The compound exhibited reddish emission in solid and solution states. The solvatochromism effect and theoretical calculation results for the excited (S₁) state of 9biAT verified that the emission was attributed to ICT transition. In particular, the structural rigidity and the orthogonal geometry around the carborane enhanced ICT-based emission in the solution state at 298 K, resulting in a considerably high quantum efficiency (Φ_em = 86%) in cyclohexane. In addition, both the Φ_em value and radiative decay constant (k_r) gradually decreased with an increase in the polarity of the organic solvent. Theoretical modelling of the charge distribution in the S₁-optimised geometry revealed that charge recombination in the radiative-relaxation process upon ICT transition could be delayed under polar conditions. Consequently, a high Φ_em value in the solution state at room temperature can be obtained by maintaining molecular rigidity and controlling the polarity of the environment.