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Journal of Physical Studies 26(4), Article 4802 [5 pages] (2022)
DOI: https://doi.org/10.30970/jps.26.4802 SPECIFICS OF THE PHOTOLUMINESCENCE OF CYTOSINE IN WATER SOLUTION
V. Shpenyk
Uzhhorod National University, 54, Voloshyna St., Uzhhorod, UA–88000, Ukraine,
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The paper presents the results of the studies into the photoluminescence of cytosine molecules in a neutral liquid medium induced by the radiation of a xenon lamp with a wavelength of 280 nm. It was found that the luminescence is represented by a wide band with a vague threshold at a wavelength of 340 nm and a blurred maximum in the spectral region of 365-380 nm. It is shown that the presented luminescence curve reflects fluorescence, while phosphorescence is absent entirely. The lack of phosphorescence can be explained by the effect of the solvent. The obtained results are compared with the data of known studies. The discrepancies found may be primarily due to the pH of the solvents used in the previous studies. It is the first time that experiments with the excitation of luminescence of a neutral liquid solution of cytosine molecules under the simultaneous action of xenon lamp radiation with a wavelength of 280 nm and a continuous laser beam with a wavelength of 530 nm and a power of 0.25 W have been performed. It has been established that under these experimental conditions the luminescence curve acquires a qualitatively new form - the luminescence threshold is shifted to the short-wavelength region, and the luminescence curve has an additional maximum at a wavelength of 410 nm. An explanation of the physical nature of this phenomenon is given, which is that the intense electromagnetic field generated by the laser promotes the efficient formation of singlet exciters of cytosine (photodimers). In the process of their decay, cytosine photodimers form excited monomers in singlet states which, by intercombinational conversion (intersystem crossing), intensively populate metastable triplet states. The radiation decay of the formed metastable triplet states causes phosphorescence, which is the reason for the appearance of the second maximum in the wavelength range of 410 nm. Attention is drawn to the fact that metastable triplet states play a key role in the photochemistry of nucleic acid bases and presumably will have a major impact on the development of new biotechnologies.
Key words: cytosine, luminescence, laser beam, excitation, molecular band, slow electrons.
