Stationary concentration of 1O2 over 1O2 quantum yield: Next level of photoactivity analysis

Abstract

The investigation of the activity of photosensitizers is a multivariate challenge for their further application in photocatalysis. Porphyrins are attractive photoactive molecules for chemical and biochemical applications, while their observed photocatalytic efficiency is a function of a variety of characteristics. In the present work the influence of porphyrin substituents on their photoactivity and photostability along with the solvent effect were studied and discussed in details. Series of experiments with 9,10-diphenylanthracene (DPA) as a selective 1O2 trap allowed to develop the approach for direct measurement of [1O2] and quantitatively evaluate the influence of various factors onto it. The processes of 1O2 relaxation, as well as its chemical and physical quenching were separated and analyzed individually. A kinetic scheme for the photosensitization process was treated with steady-state approximation to develop a mathematical apparatus, where a non-linear dependence between photosensitizer and singlet oxygen concentration was found. The general character of the derived non-linear dependence was proved experimentally for each studied porphyrin. Physical and chemical quenching rate constants of the studied porphyrins were calculated. DFT calculations allowed to find an empirical correlation between HOMO energies and observed rate constants. A plausible reaction mechanism between TPP and 1O2 was examined with Fast-NEB-TS method.