A study of the spectral and luminescence manifestations of the aggregation of thymine chromophores in polythymidylic acid aqueous solutions at room temperature in the context of photochemical information recording using thymine

Abstract

The luminescence and excitation spectra of polythymidylic acid aqueous solutions at room temperature were studied. In addition to the previously described band at 338 nm, two new bands at 320 and 350 nm were recorded at various excitation wavelengths. An examination of the excitation spectra that had not been studied previously, as well as their comparison with the differential absorption spectra previously recorded during photodimerization, allowed us to interpret the band at 320 nm as the band of noninteracting chromophores; the band at 338 nm as the band of the most photochemically active, densely packed stacking dimmers (exciton splitting of absorption band of ∼4000 cm−1); and the band at 350 nm as the band of photochemically inactive large stacking aggregates (n ≥ 10, exciton splitting of ∼8000 cm−1). The changes in the optical density of the polythymidylic acid aqueous solution at γ = 270 nm after successive irradiation of the solution with light at 279 + 302 and 248 nm were studied. The reasons for their incomplete reversibility are discussed.