PHOTOLUMINESCENCE OF SINGLET OXYGEN IN PIGMENT SOLUTIONS

Abstract

Abstract—: Luminescence of 1 O 2 (1270 nm) accompanying energy transfer to oxygen from photoexcited (triplet) molecules of sensitizers in air saturated solutions has been investigated. The luminescence was observed in CC1 4, CS 2 and freon with the use of porphyrins, chlorophylls, pheophytins and aromatic hydrocarbons as sensitizers. The lifetime and quantum yield of the luminescence depended on the nature of the solvents. pigments and their concentrations. The maximum values of these parameters were equal to 28 ± 5 ms and 5 ± 4 times 10‐‐5, respectively. The quantum yield of 1 O 2 generation by pigments has been measured and the results used for determining the quantum yields of intersystem crossing in the pigment molecules. The rate constants of 1 O 2 reaction with different substances have been determined with the aid of luminescence quenching. It has been shown that along with β‐carotene. Chls, pheophytins, and some porphyrins are also very active quenchers of 1 O 2, The quenching effect depends on their molecular structure and on the presence and nature of the central metal atom. Quenching 1 O 2 by the pigments is due mainly to a “physical” mechanism (without destruction of the pigments). The destructive “chemical” quenching is by 1–4 orders of magnitude less effective and is accompanied with photochemiluminescence of the pigments. The experiments on 1 O 2 generation and quenching indicate that energy of triplet states of bacteriochlorophyll and bacteriopheophytin is somewhat higher than that of 1 Δ g oxygen. The data demonstrate wide possibilities of the luminescence studied as a method for investigating 1 O 2 reactivity and photophysical properties of sensitizers.