Crystalline <i>o</i>-Carborane Derivatives as a Fluorescence Turning-On Probe for Acid Environments

Fluorescence from o-carborane derivatives is usually weak in solution due to the robust nonradiative decay via the motion of bond rotation, but it is enhanced in the aggregated states, which is also known as aggregation-induced emission. To the best of our knowledge, there is no other way to significantly enhance the fluorescence intensity of o-carborane derivatives in the reported literature. Also, novel strategies and sensing materials for gaseous acid detection are in high demand due to the aspects of high sensitivity, easy operation, and low cost. Herein, we report the effective fluorescence turning-on phenomenon of crystalline o-carborane derivatives upon exposure to acidic gas, which shows that crystalline o-carborane derivatives can function as effective sensors for acidic environments.