Spiro-configured fluorescent probe: Synthesis and applications in the determinations of Hg2+ and proton, and two-photon fluorescence imaging

Abstract

A novel fluorescent probe SPF-TSA was prepared by introduction of triphenylamine and dithioacetal groups on the respective biphenyl branches of 9,9′-spirobifluorene. The probing behaviors toward metal ions and pH variations were investigated via UV/Vis absorption spectra as well as one-photon fluorescence changes. SPF-TSA exhibits high sensitivity and selectivity for mercury ions and could be used to detect mercury ions even by naked eye. The detection limit of SPF-TSA for Hg2+ is at least 2.6×10−8M, which is excellent comparing with other optical sensors for Hg2+. SPF-TSA showes significantly pH-dependent spectral properties within the acidic pH-range. Especially, the pKa value of SPF-TSA is close to 6.0, which is critical for precisely assessing the acidic environments of some organelles (pH 4.5–6.8). The two-photon absorption cross-section value of SPF-TSA at 800nm is 248 GM. SPF-TSA emits strong two-photon induced fluorescence and the emission wavelength change before and after addition of Hg2+ was found to be up to140nm. Cell imaging studies demonstrate that SPF-TSA enables fluorescence imaging of both the probe and mercury ions in cells by two-photon microscopy.