Semi-empirical quantum chemical study of the formation of dimers of free base porphyrin, Mn-porphyrin and oxo-Mn-porphyrin

The dimers of porphyrin (H2P)(2), Mn-porphyrin (Mn-P)(2) and an oxo bridged Mn-porphyrin, oxo (Mn-P)(2), compounds are studied through quantum chemical semi-empirical calculations using the ZINDO program. The geometries and electronic structures of the compounds are elucidated and the electronic spectra are described at the configuration interaction level. Attention is also given to the aggregation phenomenon between the dimers. (H2P)(2) and (Mn-P)(2) present weak interactions between the macrocycles. A weak charge transfer between the pi orbitals is found for (H2P)(2). As for oxo(Mn-P)(2), a whole single bond is found for Mn-O, involving the p(x) and p(y) orbitals of the oxygen atom and d(xz) and d(yz) orbitals of manganese. The CI calculation for (H2P)(2) shows several Q, B and N transitions. For (Mn-P)(2) two characteristic Q bands were calculated and for oxo(Mn-P)(2), besides the Q and B bands, other bands are seen. (C) 1999 Elsevier Science B.V. All rights reserved.