1 May 1991 Inter- and intramolecular processes in metalloporphyrins: study by transient absorption and resonance Raman and coherent anti-Stokes Raman scattering
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Proceedings Volume 1403, Laser Applications in Life Sciences; (1991) https://doi.org/10.1117/12.57272
Event: Laser Applications in Life Sciences, 1990, Moscow, Russian Federation
Abstract
The steady interest in metalloporphyrins (Me-P) which have a central metal with an unfilled d-electronic shell is due to the rich variety of photoinduced physico-chemical processes they participate in, and by the possibility of modelling on the basis of them, the behavior of related native biological complexes. Me-Ps with an unfilled d-shell of the central atom have typical two-band absorption spectra in the ground electronic state: intense Soret or B band in the near UV and less intense Q band in the visible. According to Gouterman's fourorbital model,' the Me-P absorption spectrum arises from the promotion of ir-electrons from the highest occupied molecular orbitals a, , a2 to the lowest unoccupied orbitals e of the porphyrin conjugated macrocycle. The a, and a2 orbitals are quasi-degenerate and the electron excited configurations e have the same symmetry. That is why there is a strong mixing between the two orbital excitations a, -e and a, - e due to the configurational interaction via the electron-electron repulsion, resulting in a two-band absorption spectrum. The effect of the central atom is interpreted in this model as a perturbation of the ir-states of the porphyrin ring. The perturbation is largely determined by the electrons of the unfilled shells of the metal ion (e.g. the md'-shell). This effect is quite pronounced for the ground electronic state, nevertheless the interactions of excited ir-electronic configurations with d-electron ones cause more dramatic changes in the spectroscopic properties of Me-P excited states. New low-lying excited states are possible: the charge-transfer (CT) levels related to the electrodensity transfering from the ring a, , a2 to the d-orbitals of central metal (ir-d states) or from the d-orbitals to the ring e(d - ir states), and (d - d) levels bound up with the d-electron excitations. The present paper deals with the investigations of porphyrin metallocomplexes with nickel (Ni-P) and copper (Cu-P) having electron configurations 3d8 and 3d9 , respectively.
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Pavel A. Apanasevich, Vladimir S. Chirvony, Sergei G. Kruglik, Vladimir V. Kvach, Valentin A. Orlovich, "Inter- and intramolecular processes in metalloporphyrins: study by transient absorption and resonance Raman and coherent anti-Stokes Raman scattering", Proc. SPIE 1403, Laser Applications in Life Sciences, (1 May 1991); doi: 10.1117/12.57272; https://doi.org/10.1117/12.57272
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