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UDC 535.34Spectral-kinetic and photochemical properties of HITC dye with iodide and perchlorate counterions have been studied in environments where the dye molecules exist in different ionic forms. In ethanol, the dye molecules exist as free ions; in dichlorobenzene, as contact ion pairs. Superfast transformation of non-stationary spectra in an HITC dye bleaching band is found. The observed effects are interpreted within the framework of concepts on "burning out" a notch in the contour of a non-uniformly widened vibronic band of S 0 → S 1 -absorption. Qualitative differences in recorded absorption spectra from the dye excited electronic states for weakly and highly polar solvents are found. It is shown that the observed differences are caused by superfast charge transfer in the contact ion pairs that results in the formation of free radicals.

It is found that when indotricarbocyanine dye in HeLa cells is exposed to photons with different energies the efficiency of cell damage is wavelength independent provided the photosensitizer absorbs the same number of photons per unit time. In vivo animal experiments with two strains of tumor show that when the wavelength of the irradiating light is increased (668, 740, and 780 nm) and the number of photons absorbed per unit time per unit volume of the tumors is held constant, the damage depth increases by a factor of 1.5 and 3, respectively. The observed changes are related both to differences in the in vivo tissue optical transmission with increasing wavelength and an increased local concentration of oxygen owing to photodissociation of oxyhemoglobin.Key words: indotricarbocyanine dyes, in vivo, efficiency of photochemotherapy, wavelength of light Introduction. One of the most important parameters in the development of a new generation of sensitizers for photochemotherapy is their ability to be activated by light with wavelengths lying within the transparency region for biological tissues. The absorption bands for these compounds must lie within 700-800 nm [1-6], i.e., in the near IR. It has been shown [7, 8] that, even within the visible, moving to wavelengths with higher transmission in tissues leads to an increase in the depth to which tumors are destroyed. In the meantime, no data comparing the efficiency of photochemotherapy with light in the visible and near IR ranges have been published. This kind of study requires photosensitizers with a sufficiently wide absorption spectrum. The main absorption band of the tricarbocyanine dyes lies in the 600-800 nm range [9, 10] so that the degree of damage to tumors within this spectral range can be compared.Materials and Methods. Tricarbocyanine dye synthesized at the spectroscopy laboratory of the A. N. Sevchenko Institute of Applied Physical Problems [11] was used as a photosensitizer. Studies were carried out on a monolayer of HeLa tumor cells (planocellular cancer of the human uterine cervix) grown in a 199 nutritive medium supplemented with 10% calf blood serum and 100 mg/ml kanamycin. On completion of the light irradiation the flasks were kept in the dark for 20 h with thermostatic regulation at 37

As demonstrated by the performed studies, the molecules of tricarbocyanine dye in vivo are localized in the lowpermittivity region of the medium, predominantly in the form of contact ion pairs. Comparison of the experimental data and numerical simulation results has revealed that deformation of the dye fluorescence spectrum upon photochemotherapy is due to an increased percentage of methemoglobin (up to 50%) in the total hemoglobin concentration of a tumor tissue. A change in the photosensitizer fluorescence spectrum is observed in the area of a tumor, where laser radiation affects necrosis of the tissues. An analysis of the spectral data enables one to predict a depth and extent of the developed tumor necrosis. With the use of spectral methods, the treatment effectiveness may be optimized by the proper selection of an optimum dose and power density for photoexposure in the process of chemotherapy, with due regard for the character of pathology and individual features of a patient.

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