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Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa‐, Cyclohepta‐, and Cyclooctapyrrole
Author(s) -
Gorski Alexander,
Köhler Thomas,
Seidel Daniel,
Lee Jeong Tae,
Orzanowska Grażyna,
Sessler Jonathan L.,
Waluk Jacek
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200401343
Subject(s) - magnetic circular dichroism , degenerate energy levels , x ray magnetic circular dichroism , vibrational circular dichroism , chemistry , circular dichroism , excited state , spectral line , atomic orbital , electronic structure , absorption spectroscopy , molecular physics , atomic physics , crystallography , physics , computational chemistry , optics , quantum mechanics , electron
Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter‐model‐based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained.