Subtle structural variation in azine/imine derivatives controls Zn(2+) sensitivity: ESIPT-CHEF combination for nano-molar detection of Zn(2+) with DFT support

Excited-state intra-molecular proton transfer (ESIPT)-active imine and azine derivatives, structurally characterised by XRD, and denoted L1, L2, L3 and L4, possess weak fluorescence. The interaction of these probes with Zn(2+) turns ON the fluorescence to allow its nano-molar detection. Among the four ESIPT-active molecules, L2, L3 and L4 are bis-imine derivatives while L1 is a mono-imine derivative. Among the three bis-imine derivatives, one is symmetric (L3) while L2 and L4 are unsymmetrical. The lowest detection limits (DL) of L1, L2, L3 and L4 for Zn(2+) are 32.66 nM, 36.16 nM, 15.20 nM and 33.50 nM respectively. All the probes bind Zn(2+) (10(5) M(−1) order) strongly. Computational studies explore the orbital level interactions responsible for the associated photo-physical processes.