Role of Multicenter Interactions in the Formation of Spectral-Luminescent Characteristics of 5,15-Diphenylporphyrin Derivatives

Abstract

The peculiarities of formation of spectral-luminescent characteristics of 5,15-diphenylporphyrin derivatives with various architecture of peripheral substitution have been studied. Molecular conformation of the derivatives with various peripheral substituents in С_b and С_m-positions of the tetrapyrrole macrocycle was optimized with a density functional method. It has been shown that substitution of two diametrally opposite С_m-atoms leads to the macrocycle elongation in the direction of substitution which does not depend on С_b-substitution character; and dodecasubstituted derivatives are of a saddle-shaped character of macrocycle distortion. The quantum yield of 5,15-diphenylporphyrin fluorescence and its С_b-alkylated derivatives reduces in comparison with that of 5,10,15,20-tetraphenylporphyrin, and the attachment of nitrogroups and bromine atoms in para-position of the phenyl fragments leads to rising and quenching of the fluorescence respectively. It has been established that the attachment of two nitrogroups in С_m-positions of 5,15-diphenylporphyrin macrocycle leads to substantial bathochromic shifts of the absorption and fluorescence spectra with 100-fold fluorescence quenching due to significant gain of nonradiative deactivation of S1-state upon the saddle-shaped conformer formation.