Electronic structures of azulene-fused porphyrins as seen by magnetic circular dichroism and TD-DFT calculations.
A combination of magnetic circular dichroism (MCD), electronic absorption spectroscopy and time-dependent density functional theory (TD-DFT) calculations has been used to investigate the electronic structure of azulene-fused pi-expanded porphyrins based primarily on the spectral properties of absorption bands in the near infrared region. From MCD experiments, it was suggested that in the case of a mono-azulene-fused porphyrin DeltaHOMO approximately equal DeltaLUMO (where DeltaHOMO is the magnitude of the energy gap between the HOMO and HOMO-1 and DeltaLUMO is the magnitude of the energy gap between the LUMO and LUMO+1), while in the case of an oppositely-di-azulene-fused porphyrin, DeltaHOMO<DeltaLUMO. Since Faraday A terms are observed for both the Soret and Q bands in the MCD spectrum of tetra-azulene-fused porphyrin the corresponding excited states are clearly accidentally degenerate despite the C(2) molecular symmetry. Transition dipole moment analysis clearly demonstrates that the electronic absorption spectrum of tetra-azulene-fused porphyrin has out-of-plane electronic transitions slightly to the blue of the main Q and Soret bands. Comparison with distorted porphyrins and phthalocyanines strongly suggests that these out-of-plane transitions appear as intense Gaussian-shaped Faraday B terms in the MCD spectra.
Nakai
Katsunori
K
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
Kurotobi
Kei
K
Osuka
Atsuhiro
A
Uchiyama
Masanobu
M
Kobayashi
Nagao
N
D052176:Azulenes / Q000737:chemistry*; D002942:Circular Dichroism; D003198:Computer Simulation; D008958:Models, Molecular; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*
D052176:Azulenes; D011166:Porphyrins; C005525:azulene