A new perylene-based fluorescent pH chemosensor for strongly acidic condition.

A highly selective and sensitive pH chemosensor N,N-bis[(2-thiophene)-ethyl]-3,4,9,10-perylene tetracarboxylic diimide (TEPTD) was designed and synthesized through Schiff-base condensation reaction. It exhibited large Stokes shifts, good water solubility, excellent selectivity and outstanding photo-stability. The pKa of the probe was 3.0, which indicated that it could be used in highly acid conditions. With the addition of H+, the fluorescence intensity increased gradually. The sensing mechanisms involved photo-induced electron transfer, protonation and deprotonation, which were confirmed by 1H NMR titration experiment with trifluoroacetic acid. The probe can be used as a convenient probe to distinguish acidic from neutral or alkaline solutions by "naked-eye".