Theoretical Study On The Excited States And The Vibronic Fine-structure Spectra Of Cis-H₂iBC And Psoralen

cis-H₂iBC and Psoralen have a wide range of applications in various fields due to their unique photophysical,photochemical and photobiological properties.It is so important to study them because these macromolecules play an important role in the life.On the basis of density functional theory and its time-dependent extension,the structure optimization and frequency calculation of the ground state and the first excited state of cis-H₂iBC and Psoralen were carried out,the vertical excitation energies,oscillator strengths and electronic transition moments of low-lying excited states(S_1,S_2,S₃)were also obtained.The high-resolved spectra of Q band of cis-H₂iBC and Psoralen were simulated in the framework of the Franck-Condon?FC?approximation.For cis-H₂iBC,the effects of the Herzberg–Teller and the Duschinsky effect on the spectral simulation were taken into consideration.For Psoralen,we focused on the effect of solvent effects on the spectral simulation.1.Theoretical Study of Excited States and Fine Structure Spectra of cis-H₂iBC?1?.Equilibrium structures together with frequencies of the ground-and excited-states for cis-H₂iBC were calculated by using B3LYP,PBE0and BHandHLYP combined with 6-311G?d,p?basis set,all calculations,including the vertical excitation energies,oscillator strengths and electronic transition moments of low-lying excited states(S_1,S_2,S₃)were performed in the Gaussian09 suite of programs.Structural parameters and spectral constants were obtained for subsequent spectral simulations.?2?The investigations on the structures and intensities of the vibrational spectrum of the electronic vibrational absorption and fluorescence spectra of cis-H₂iBC.Using a harmonic model and taking into account the Duschinsky and the Herzberg–Teller effects,the Franck-Condon overlap integral is calculated in the electronic transition.Combining quantum chemical calculations with the calculated Franck-Condon factor,the intensity of the high-resolved electronic vibrational absorption and fluorescence spectra were theoretically obtained.?3?The spectral simulations for experimentally obtained the absorption and fluorescence spectrum were carried out.The simulated spectra agreed well with the experimental spectrum considering both Duschinsky and Herzberg–Teller effects.The theoretical results allowed to identify the experimental bands and to assign them to the specific vibrational transitions.The individual Herzberg-Teller and Duschinsky effects were investigated separately and their respective contributions on the vibrational intensity changes of different normal modes were clarified.2.Theoretical Study of Excited States and Fine Structure Spectra of Psoralen?1?On the basis of density functional theory and its time-dependent extension,the equilibrium structures together with frequencies of the Psoralen molecule were calculated in the framework of DFT for the S₀state and TDDFT for the S₁ state.The vertical excitation energies,oscillator strengths and electronic transition moments of low-lying excited states?S₁,S₂,S₃?were also calculated.All calculations were performed in the 6-31+g?d,p?basis set,and the structures and intensities of the vibrational spectrum of the electronic vibrational absorption and fluorescence spectra of Psoralen were investigated.Using a harmonic model,combining quantum chemical calculations with the calculated Franck-Condon factor,the intensity of the high-resolved electronic vibrational absorption and fluorescence spectra were theoretically obtained.?2?In this work,we consider the effect of solvent effect on simulated electronic vibrational absorption and fluorescence spectra of Psoralen,using the Polarisable Continuum Model?PCM?to simulate solvent effect.The absorption spectrum and fluorescence spectrum of Psoralen were simulated in different solvents?gas phase,ethanol and cyclohexane?.The simulated spectra in the gas phase agreed well with the experimental spectrum and allowed to identify most of experimental bands.The spectral intensity of the simulated absorption and fluorescence spectra in ethanol is significantly stronger than that in cyclohexane.