Theoretical Study on Resonance Raman Spectra of Tetraoxaporphyrin Dication by TDDFT Calculation

The B state excited resonance Raman scattering of tetraoxaporphyrin dication (TOP) was theoretically studied with DFT/TDDFT calculations and the sum-over-states approach of polarizability including both the A and B terms contributions. The resonance Raman spectra calculated with PBE1PBE, B3LYP, Cam-B3LYP, and B3LYP-D3 functionals are similar to each other in general, with PBE1PBE and B3LYP being better in reproducing resonance Raman intensities in comparison with the experiment. The calculated relative intensities of the totally symmetric modes are excellently consistent with the experiment. The TDDFT calculations manifested a considerable deformation of the B state along the ν2, ν6, ν7, and ν8 modes, which is responsible for the strong resonance Raman intensities of these modes. The resonance Raman intensities of non-totally symmetric modes were calculated to be weaker than the totally symmetric modes by one or two order of magnitude, which qualitatively agrees with the experiment. However, the resonance Raman intensity of the ν10 mode (CβCβ stretch, B1g symmetry) predicted by TDDFT calculations is unexpectedly small whereas that of the ν11 mode (symmetric CαCm stretch, B1g symmetry) is too large, which is assumed to be caused by the Jahn-Teller instability for the B state of TOP.