The Photosalient Effect and Thermochromic Luminescence Based on o‐Carborane‐Assisted π‐Stacking in the Crystalline State.

Herein, we report the unique multiple‐stimuli responsiveness of anthracene‐tethered o‐carborane derivatives. We designed and synthesized anthracene derivatives with different substitution positions and numbers of the o‐carborane units. Two compounds had characteristic crystal structures involving the columnar π‐stacking structures of the anthracene units. From the analysis of crystalline‐state structure–property relationships, it was revealed that the crystals exhibited the photosalient effect accompanied by photochemical [4+4] cycloaddition reactions and temperature‐dependent photophysical dual‐emission properties including excimer emission of anthracene. Those properties were considered as non‐radiative and radiative deactivation pathways through the excimer formation in the excited state and the formation of excimer species was facilitated by the π‐stacking structure of anthracene units. Moreover, we found unusual temperature dependency on the occurrence of the photosalient effect. According to the data from variable temperature X‐ray crystallography, a strong correlation between lattice shrinkage and strain accumulation is suggested. [ABSTRACT FROM AUTHOR]