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A two-photon fluorescent probe ( DMPCA ) for the detection of bisulfite anion in water was developed based on twisted-intramolecular-charge-transfer (TICT) mechanism. Fluorescence intensity of DMPCA increased dramatically (65 fold) upon the addition of HSO 3 − . The two-photon absorption cross-section of DMPCA was found to be 725 GM at 700 nm upon the addition of HSO 3 − . The fluorescent probe showed an excellent selectivity for bisulfite anion over other anions. The nucleophilic addition reaction mechanism with aldehyde was confirmed with NMR and MALDI-TOF. The TICT detection mechanism was confirmed by viscosity-dependent fluorescence spectra and time resolved fluorescence spectra. Moreover, DMPCA was successfully applied to the detection of bisulfite anion in HeLa cells with low cytotoxicity under two-photon excitation. [ABSTRACT FROM AUTHOR]

A two-photon fluorescent probe ( NQ ) for cysteine (Cys) and homocysteine (Hcy) was developed based on twisted-intramolecular-charge-transfer (TICT) mechanism. NQ showed excellent “OFF–ON” fluorescence (at 540 nm) detection signal on addition of Cys/Hcy with high selectivity. The detection mechanism was successfully proved by theoretical calculations, viscosity dependent fluorescence and time resolved fluorescence spectra. NQ exhibits large two-photon absorption (TPA) cross-section with Cys/Hcy (580 and 710 GM) at nearly 800 nm, respectively. Cell-culture results indicated that NQ was cell-permeable and could be used to detect Cys/Hcy with low cytotoxicity under two-photon excitation in living cells. To our best knowledge, NQ is the first TICT based two-photon fluorescent probe for Cys/Hcy. [ABSTRACT FROM AUTHOR]