Rational design for thermochromic luminescence in amorphous polystyrene films with bis-o-carborane-substituted enhanced conjugated molecule having aggregation-induced luminochromism

Abstract

We designed the triad molecule, bis-o-carborane-substituted bis(thienylethynyl)benzene, as a filler for realizing thermochromic luminescent behaviors based on conventional polymer films, such as polystyrene. From the optical measurements, it was found that the triad can show solid-state emission and dual-luminescent properties with variable intensity ratios depending on media. From the mechanistic studies including the experiments with the methyl-substituted model compound, it was revealed that dual emission should be originated from the locally excited and twisted intramolecular charge transfer states, and the latter emission band is significantly enhanced in the solid states. We prepared amorphous films containing variable concentrations of the triad with the spin-coating method and investigated optical properties. It was found that intensity ratios were drastically changed by altering the concentration of the triad. By increasing the proportion of the triad, aggregation occurred, and emission color was apparently varied through the changes in intensity ratios of the dual emission property. Based on the aggregation-induced luminochromic property of the triad, thermochromic luminescence was finally realized by heating the amorphous films. The rational design for obtaining thermochromic luminescent amorphous films is illustrated in this paper.