Modulation of the optical properties of chiral porphyrin dimers by introducing bridged chiral amide-bonds

Abstract

The d/l-enantiomers of a series of three Zn(II)tetraarylporphyrin dimers were synthesized and isolated by incorporating a bridging amide-bonded xanthene moiety at the para-position of one of the meso-aryl rings. The electronic structures and optical properties were modulated by incorporating chiral amino acid moieties into the amide-bonding moieties of the xanthene bridge that contain methyl, tolyl and 2-methylindole substituents. A cofacial dimer was formed in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) resulting in a significant red shift of the B band, due to a relative destabilization of the HOMO, which has large MO coefficients on the pyrrole nitrogens. The sign sequences observed in the B band region of the CD spectra due to the presence of the chiral amino acid moieties were modified due to this change in geometry. Significant CD intensity is also observed in the B band region of the CD spectra of anion radical species during in situ spectroelectrochemical measurements.

Lipophilic Corrole-Porphyrin-Corrole Linear Triad

“…The optical spectroscopy of corrole and their analogues can be understood based on a consideration of perturbations to an M L = 0, ±1, ±2, ±3, ±4, ±5, ±6 and ±7 sequence in ascending energy terms for the orbital angular momentum quantum number for the MOs of a D 15h symmetry parent hydrocarbon perimeter. The HOMO and LUMO have M L = ±4 and ±5, respectively, and are linked by forbidden and allowed ΔM L = ±9 and ±1 transitions, which are associated with the Q and B bands of Gouterman's four-orbital model, [12] respectively, that are observed in the 500-600 and 400-450 nm regions of UV-Vis spectra. The absorption spectrum of 4 in lowpolar CH 2 Cl 2 contains a splitted intense B band at λ = 422 and 433 nm with an unclear shoulder band at slightly longer wavelength region, while five relatively intense bands are observed in the Q band region at 516, 556, 570, 612 and 645 nm.…”