title: Magnetic circular dichroism study of directly fused porphyrins.
abstract: The magnetic circular dichroism (MCD) spectra of doubly and triply linked fused bisporphyrins (2MD and 2MT, M = Ni, Zn, Cu, Pd, and H2) and triply linked higher oligomers (3ZnT and 4ZnT) have been measured, and their Q-bands assigned based on the results of INDO/s calculations. In contrast to the Faraday A term observed for the Q(0,0) band of Ni(II) tetraphenylporphyrin, a single positive Faraday B term was observed for the lowest energy transition of the fused systems. The calculations indicated that the molecular orbitals (MOs) of the directly fused porphyrins consist of linear combinations of the constituent monomeric MOs, and that the effect of lowering the symmetry is always larger on the lowest unoccupied molecular orbital (LUMO) than on the highest occupied molecular orbital (HOMO). On the basis of Michl's perimeter model, these features can be correlated with the observed positive MCD signs in the near infrared region. A weak absorption band at 600-700 nm for the fused dimers can be assigned to a short-axis polarized Q transition.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Atsuya
authors.initials: A
authors.lastname: Muranaka
authors.forename: Masaki
authors.initials: M
authors.lastname: Yokoyama
authors.forename: Yotaro
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Masanobu
authors.initials: M
authors.lastname: Uchiyama
authors.forename: Akihiko
authors.initials: A
authors.lastname: Tsuda
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka
authors.forename: Nagao
authors.initials: N
authors.lastname: Kobayashi