A squaraine-based fluorescence turn on chemosensor with ICT character for highly selective and sensitive detection of Al in aqueous media and its application in living cell imaging.

A novel and simple squaraine-based fluorescent chemosensor SQ-BH bearing the benzoylhydrazine moiety was developed for the highly sensitive and selective detection of Al in methanol-water mixture. The chemosensing behaviors of SQ-BH and its binding interaction with Al were explored by various spectroscopic analyses. The reversibility of Al recognition process was investigated using EDTA. The results of experiments and DFT/TDDFT calculations revealed that the chemosensor SQ-BH obeyed a turn on mechanism which was associated with the inhibited photoinduced electron transfer (PET), the enhanced intramolecular charge transfer (ICT) and the activated chelation enhanced fluorescence (CHEF). Furthermore, the fluorescent chemosensor SQ-BH whose excellent biocompatibility was confirmed by a standard MTT assay could be used to detect Al in living cells, indicating its potential application value in biological fields.