Ultrafast excited-state proton transfer dynamics of 1,8-dihydroxyanthraquinone (chrysazin) studied by femtosecond time-resolved fluorescence spectroscopy

Femtosecond time-resolved fluorescence intensities of 1,8-dihydroxyanthraquinone (chrysazin) in hexane have been measured at room temperature for a wide visible wavelength region (470–670 nm) by using the up-conversion method. Time-resolved fluorescence spectra were reconstructed after deconvolution taking account of the finite instrumental response. It was found that both the `normal-form typeʹ fluorescence and the `tautomeric-form typeʹ fluorescence appear almost instantaneously, which indicates that a barrierless excited-state proton transfer occurs within 50 fs reflecting delocalization of the excited-state wave function. A fluorescence spectral change was also observed in a few picosecond time scale, which was assigned to an additional proton translocation induced by the intramolecular vibrational relaxation.