ESIPT triggered TICT of an Al³⁺ fluorescence sensor and its sensing mechanism

Excited state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) play fundamental roles during the excited state dynamics of dyes and fluorescent sensors. In this contribution, the ESIPT process is demonstrated to trigger the TICT process during the photo-physical process of a turn-on Al3+ sensor. The non-emissive TICT state can be facilely reached after the photo excitation and the ESIPT process, which quenches the fluorescence of the sensor. Al3+ is demonstrated to coordinate with the sensor and lock the twisted of the sensor, which eliminates the TICT state and turns on the fluorescence. Selective of the sensor is also revealed by study the interaction and electron transfer between the sensor and Cr3+.