Photonics of dissolved oxygen molecules. Comparison of the rates of direct and photosensitized excitation of oxygen and reevaluation of the oxygen absorption coefficients

The rates of photooxygenation of singlet oxygen traps (1,3-diphenylisobensofuran, tetracene and rubrene) were compared in air-saturated carbon tetrachloride upon porphyrin-photosensitized and direct excitation of oxygen molecules. At equal power of incident radiation, the ratio of oxygen excitation rates normalized to porphyrin absorbance was found to be similar to 10(4). Continuous and pulse (peak power <= 20 MW/cm(2)) laser radiation of equal average power caused similar rates of direct oxygen excitation. Improved procedure of data analysis was developed and accurate values of absorbance A(max), molar absorption coefficient epsilon(max) and the cross section of light absorption sigma(max) were obtained for the oxygen absorption maxima at 1273, 765 nm and 1073 nm. The results were employed for reevaluation of the absorption coefficients of oxygen in other solvents, which were studied using carbon tetrachloride as the reference. It was found that the ratios A(1273)/A(765); epsilon(1273)/epsilon(765) and sigma(1273)/sigma(765), which were equal to 7/1 in carbon tetrachloride, decreased in polar solvents and reached 1.5/1 in water. This effect was shown to be due to the decrease of epsilon(1273) and sigma(1273) on going from non-polar solvents to water, whereas epsilon(765) and sigma(765) are less sensitive to solvents and slightly increased with the increase of solvent polarity. The obtained data are important for dosimetry of laser radiation in biomedical experiments and suggest that the radiation at 765 nm is more appropriate for oxygen excitation in biological systems since its efficiency is similar to that of the radiation at 1273 mm, but dark red light penetrates deeper into tissues and causes weaker heating of water. (C) 2016 Elsevier B.V. All rights reserved.