Direction Switching and Self-Recovering Mechanochromic Luminescence of Anthracene-Modified o-Carboranes.

Luminochromic behaviors regarding mechanochromic luminescence (MCL) of o-carborane-modified anthracene derivatives are reported. We have previously synthesized bis-o-carborane-substituted anthracene and found that its crystal polymorphs show dual-emission properties composed of excimer and charge transfer (CT) emission bands in the solid state. Initially, we observed the bathochromic MCL behavior from 1 a originating from emission mechanism alteration from dual emission to CT emission. By inserting the ethynylene spacers between anthracene and o-carboranes, compound 2 was obtained. Interestingly, 2 showed hypsochromic MCL originating from the emission mechanism alteration from CT to excimer emission. Furthermore, luminescent color of ground 1 a can be recovered to the initial state by allowing to stand at room temperature, meaning that self-recovery proceeds. Detailed analyses are described in this study.