Fig. 1. Synthesis of dibenzothiophene-based fluorescent probe.

Fig. 2. Normalized UV absorption and one-photon fluorescence (FL) spectra of TP and TPI in DMF, [TPI]=10−5  mol/L.

Fig. 3. Two-photon fluorescence spectra of TPI and DAPI in DMF, [TPI]=[DAPI]=10−4  mol/L.

Fig. 4. (a) and (c) UV absorption and OPEF responses of DAPI and (b) and (d) TPI upon the titration of DNA in the Tris-HCl buffer solutions, [TPI]=[DAPI]=10−5  mol/L, [DNA]=0−1.3×10−3  mol/L.

Fig. 5. One-photon and two-photon confocal fluorescence images of 3T3 cells stained with TPI (0.5 μmol/L) for 3 h. (a) TPEF bioimaging; (b) DIC picture; (c) OPEF bioimaging; (d) Merged bioimaging of a and c. The wavelength for two-photon and one-photon excitation was 800 and 405 nm, respectively. Scale bar was 50 μm.

Fig. 6. Confocal fluorescence images of 3T3 cells co-stained with TPI (0.5 μmol/L) and MTR (0.5 μmol/L). For TPI, λex=405  nm, and λem=525−575  nm. For MTR, λex=575  nm, and λem=585−660  nm. Scale bar was 50 μm.

Fig. 7. Time-dependent confocal fluorescence bioimaging of 3T3 cells stained with TPI (0.5 μmol/L) for 15 min. The excitation wavelength was 800 nm. Scale bar was 50 μm.

Fig. 8. Time-dependent confocal fluorescence bioimaging of 3T3 cells stained with DAPI (0.5 μmol/L) for 15 min. The excitation wavelength was 740 nm. Scale bar was 20 μm.

Fig. 9. Comparison of photostability of TPI and DAPI under successive irradiation.