New water-soluble dicyano-stilbene dyes: One and two-photon fluorescence and photo-response to BSA

Two novel quadrapolar stilbene fluorescent dyes with CN groups (DCNs) are reported. Photophysical properties such as fluorescence, intermolecular charge transfer, two-photon absorption action cross section (δФ) and fluorescence-response to bovine serum albumin (BSA) are investigated and discussed. The fluorescence emission is red-shifted and quenched with the increase in polarity of solvents. In aqueous buffer (pH 7.0), compound 1b has a large blue shift (74 nm) and 37-fold fluorescence enhancement when interacts with BSA. The response is noticeable by naked eyes. Cations, anions and DNA have no such responses. It is resulted from the change of environmental polarity from aqueous solution to hydrophobic cage in protein, and sequentially, the change in the effect of excited intermolecular charge transfer.