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.