Electronic levels and vibrational structure of the cis form of a cyano derivative of methylated isobacteriochlorin

Abstract

Isobacteriochlorins, tetrahydroporphin derivatives with adjacent hydrogenated pyrrole rings (iBC), are of great importance in biochemistry as prosthetic groups of redox enzymes (siroheme) and intermediates in vitamin B12 biosynthesis. The quasi-line vibronic fluorescence and absorption spectra of unsubstituted iBC in the trans form were first obtained at 77 K [i] and then at 4.2 K [2] (see also [3], pp. 331-342); a parallel investigation was made of bacteriochlorin (BC), a tetrahydroporphin with an opposite arrangement of the hydrogenated pyrrole rings. In [2] a method of determining the polarization of vibronic transitions and the symmetry of the normal vibrations of molecules, based on a study of the anisotropy of the emission of a doped n-aikane single crystal, proposed in [4], was used. The spectroscopic data confirmed the presence of a center of symmetry in the BC molecule and its absence in the iBC molecule. The quasi-line spectra (QLS) of BC were also investigated in [5].