Electronic structure, spectra, and magnetic circular dichroism of cyclohexa-, cyclohepta-, and cyclooctapyrrole.
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.
Gorski
Alexander
A
Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland.
Köhler
Thomas
T
Seidel
Daniel
D
Lee
Jeong Tae
JT
Orzanowska
Grazyna
G
Sessler
Jonathan L
JL
Waluk
Jacek
J
D002942:Circular Dichroism; D011758:Pyrroles / Q000737:chemistry*; D013057:Spectrum Analysis
D011758:Pyrroles