Responsive mechanism and coordination mode effect of a bipyridine-based two-photon fluorescent probe for zinc ion**Project supported by the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM026).

Abstract

The properties of one-photon absorption (OPA), emission and two-photon absorption (TPA) of a bipyridine-based zinc ion probe are investigated employing the density functional theory in combination with response functions. The responsive mechanism and coordination mode effect are explored. The structural fluctuation is illustrated by molecular dynamics simulation. The calculated OPA and emission wavelengths of the probe are consistent with the experimental data. It is found that the red-shift of OPA wavelength and the enhancement of TPA intensity are induced by the increased intra-molecular charge transfer mechanism upon metal binding. The structural fluctuation could result in the blue-shift of TPA wavelength and the decrease of the TPA cross section. The TPA properties are quite different among the zinc complexes with different coordination modes. The TPA wavelength of the complexes with two ligands is close to that of the probe, which is in agreement with the experimental observation.