Abstract:
A bipyridine centered donor–acceptor–donor (D–p–A–p–D) type ratiometricfluorescent molecular
probe exhibited an unprecedented enhancement in the two-photon absorption (2PA) cross section upon Zn2+ binding. Moreover, owing to the excited state charge-transfer of thefluorophorep-backbone, a
significant enhancement in the two-photon (2P) excitedfluorescence intensity was observed upon Zn 2+
binding, resulting in a 13-fold enhancement in the 2PA cross section and a 9-fold enhancement in
fluorescence brightness at 620 nm when compared to the cation-freefluorophore. The large 2PA cross
section of 1433 GM and 2P action cross section (860 GM), with an excellent 2P excitedfluorescence
variation from 517 to 620 nm upon Zn 2+ binding, facilitated the ratiometric monitoring of free zinc ions
in cells. The low cytotoxicity and good photostability of the fluorophore allowed two-photon Zn2+
imaging of HeLa cells. In addition, in vivo two-photon imaging of Zn2+ ions in hepatocytes of live rats illustrated the viability of the probe in tissue imaging and monitoring of free zinc ions in live cells
