TD-DFT analysis of photoinduced distortions and vibronic absorption of the malachite green dye in aqueous solution
摘要
The dye conformations were described regarding φ torsions between the planes of the phenyl rings and their σ bonds with the central carbon atom. Twenty-one hybrid functionals with different portions of the exact Hartree–Fock exchange were used to calculate the dye structures in the ground and the first and second excited states. For the first time, we analyzed the values of the θ valence angles between the σ bonds of the central carbon atom. We found twelve very strong correlations between the θ and φ values in various combinations. The MN15 functional gives a good agreement between the calculated vibronic absorption spectrum and the experimental one, both in the position of the maximum and in the shape. In this case, only low-frequency vibrations of large atomic groups in the S1 excited state are involved in vibronic transitions, which may be responsible for the ultrafast relaxation of the dye in solution. All quantum chemical calculations were performed using the Gaussian16 software package. We used a set of twenty-one hybrid functionals that differed, among other parameters, in the fraction of the exact Hartree–Fock exchange. The 6-311++G (d,p) basis set and the IEFPCM solvent model were applied.