Vibrational states of Zn-meso-indolo[3,2-b]carbazolyl-substituted porphyrins: Fluorescence line narrowing study

Highly resolved vibrational spectra for the Zn-complexes of several meso-substituted tetraarylporphyrins were recorded by fluorescence line narrowing (FLN) method at liquid helium temperature. The frequencies of the vibronic lines of the Zn-5,10,15,20-tetraphenylporphyrin (ZnTPP), the Zn-5,10,15,20-tetramesitylporphyrin (ZnTMesP) and four meso-indolocarbazolyl-substituted porphyrin compounds in the FLN spectra have been measured and compared. The frequencies, maximum amplitude changes for natural coordinates and the symmetry of the normal modes for ZnTPP and ZnTMesP were also determined on the basis of DFT quantum-chemical calculations. Differences in the orientation of the meso-aryl rings for ZnTPP and ZnTMesP have been identified and discussed. An explanation for the spectral changes upon substitution with indolo[3,2-b]carbazole units is given providing further elucidation on the structural features arising upon the progressive substitution with ICZ groups.