Interpretation of the UV-vis spectra of the meso(ferrocenyl)-containing porphyrins using a TDDFT approach: is Gouterman's classic four-orbital model still in play?

Abstract

The vertical excitation energies of H_2TPP [TPP = 5,10,15,20-tetraphenylporphyrin(2-)], H_2FcPh_3P [FcPh_3P = 5-ferrocenyl-10,15,20-triphenylporphyrin(2-)], cis-H_2Fc_2Ph_2P [cis-Fc_2Ph_2P = 5,10-bisferrocenyl-15,20-diphenylporphyrin (2-)], trans-H_2Fc_2Ph_2P [trans-Fc_2Ph_2P = 5,15-bisferrocenyl-10,20-diphenylporphyrin(2-)], H_2Fc_3PhP [H_2Fc_3PhP = 5,10,15-trisferrocenyl-20-phenylporphyrin(2-)], and H_2TFcP [TFcP = 5,10,15,20-tetraferrocenylporphyrin(2-)] were investigated using a time-dependent density functional theory (DFT) approach and compared to their experimental UV-vis spectra in the 10,000-30,000 cm^(-1) region. It was shown that the lowest energy transitions in meso(ferrocenyl)-containing porphyrins have predominantly ferrocene-to-porphyrin charge transfer character, while the porphyrin-centered π-π* transitions predicted by the Gouterman's classic four-orbital model still have the largest intensities in the UV-vis region. The number of predominantly ferrocene-to-porphyrin charge transfer transitions increases with the number of ferrocene substituents and becomes dominant in H_2TFcP.

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