Direction Switching and Self‐recovering Mechanochromic Luminescence of Anthracene‐modified o‐Carboranes

We report luminochromic behaviors regarding mechanochromic luminescence (MCL) of o-carborane-modified anthracene derivatives. We have previously synthesized bis-o-carborane-substituted anthracene 1 and found that its crystal polymorph 1a show dual-emission properties composed of excimer and charge transfer (CT) emission bands in solid. Initially, we observed the bathchromic MCL behavior from 1a 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 1a 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.