HOLE-BURNING STUDY OF PRIMARY PHOTOCHEMISTRY OF METALLOPORPHYRINS IN REACTIVE SOLVENT GLASSES

Intermolecular photoprocesses in glassy solutions of magnesium octaeth ylporphine (MgOEP) and zinc tetrabenzoporphine (ZnTBP) have been inves tigated under one- and two-color irradiation between 8 and 80 K. The s imultaneous exposure to the pulsed laser light in resonance with the 0 -0 S-1 <-- S-0 transition and the continuous blue light absorbed by th e Tn <-- T-1 transitions leads to a much faster hole burning than the irradiation with the laser light alone. This photon gating effect is o bserved in many reactive solvent glasses or the mixtures of a reactive component and the inert diluent. In solvent glasses containing electr on accepters (alkyl halogenides, tert-butyl peroxybenzoate, ethyl diaz oacetate) the two-quantum photooxidation results in the bleaching of p orphyrin absorption bands and formation of cation radical absorption a t 650-700 nm (in the case of MgOEP). In the presence of electron donor s (triethylamine) and alkenes the photoreaction can be observed only i n the hole-burning regime because upon broad-band irradiation the inte nsity and position of the 0-0 band remain unchanged. The hole burning in these systems stems from sensitized photoprocesses leading to the r earrangement of pigment environment. The microscopic solvent shift of the zero-phonon transition frequency of the pigment following cis-tran s isomerization of the alkene molecules or reversible electron transfe r results in the formation of a dip in absorption. In this case ''anti holes'' are observed as a result of intensity redistribution within th e 0-0 band. Depending on the height of the triplet level of the alkene , the sensitization can take place by means of tripler energy transfer from either the T-n or T-1 state (to cyclooctatetraene) of the pigmen t. The influence of concentration, chemical structure, reduction poten tial, and the height of tripler energy level of activators as well as the matrix properties on the efficiency of gated hole burning has been investigated. The reactivities of aliphatic halocarbons and amines, a romatic electron accepters and donors, cyclic and linear olefins with and without electron-accepting substituents, and other compounds have been studied. The most efficient sensitizers have been selected and do ped in the polymer films which are more convenient for the application s of spectral hole burning in optical data storage.