TDDFT study of UV-vis spectra of permethrin, cypermethrin and their beta-cyclodextrin inclusion complexes: a comparison of dispersion correction DFT (DFT-D3) and DFT.

A comparative study of DFT and DFT-D3 has been carried out on the UV-vis absorption of permethrin, cypermethrin and their β-cyclodextrin inclusion complexes. The TDDFT method with PCM (or COSMO) model was adopted and B3LYP, BLYP and BLYP-D3 functionals were selected. Comparing the simulated spectra with experimental one, we can notice that pure BLYP functional can better reproduce the UV-vis spectra than hybrid B3LYP, but empirical dispersion corrections BLYP-D3 has better performance than BLYP. BLYP-D3 calculations reveal that the main absorption bands of permethrin and cypermethrin arise from the π→π(*) transition, after encapsulated by β-CD to form inclusion complexes, the host-guest intermolecular charge transfer (ICT) makes the main absorption bands to be changed significantly in wavelength and intensity.