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The molecular structure and properties of the two lowest singlet electronic states(1La and 1Lb states)of indole and its derivatives were studied to improve current understanding of the photophysical behavior of biochemical probes in the characterization of protein properties.1 The 1La geometry was found to be very close to the conical intersection,connecting the 1La and 1Lb states.2 We should make sure which state(1La or 1Lb)was the first singlet excited(S1).Structures,energies,and dipole moments of indole and its derivatives were reported for all three states(ground,1La and 1Lb states)and compared to experimental values with time-dependent density functional theory(TD-DFT).Results showed that all of the hybrid and meta-GGA functionals predicted a wrong order of 1La and 1Lb states in indole and azaindole while they were all right in indene and benzimidazole.Their absorption and emission spectra of the first singlet excited states were investigated with harmonic Franck-Condon(FC)simulation including Herzberg-Teller(HT)and Duschinsky effects for indole and its derivatives.Furthermore,anharmonicity was also taken into account for the excited state potential energy surfaces.Quite good agreement between the experimental and the FCHT simulated absorption and emission spectra were found(only PBE0/6-311+G(2d,p)for benzimidazole was list in the abstract(Fig 1-3)).The effect of first-order anharmonic correction was not very obviously,just made spectral peak positions shift and intensities change for absorption and emission spectra.3 It should be emphasized that the HT and Duschinsky effects were great important to provide full and rich vibronic structure.We expect that the present theoretical methods in the paper could be as a reference for the fine electronic spectra simulation of these molecules.