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 chemica l semi-empirical calculations using the ZINDO program. The geometries and e lectronic structures of the compounds are elucidated and the electronic spe ctra are described at the configuration interaction level. Attention is als o given to the aggregation phenomenon between the dimers. (H2P)(2) and (Mn- P)(2) present weak interactions between the macrocycles. A weak charge tran sfer 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 o f the oxygen atom and d(xz) and d(yz) orbitals of manganese. The CI calcula tion for (H2P)(2) shows several Q, B and N transitions. For (Mn-P)(2) two c haracteristic Q bands were calculated and for oxo(Mn-P)(2), besides the Q a nd B bands, other bands are seen. (C) 1999 Elsevier Science B.V. All rights reserved.