The Synthesis And Photochemical Study Of Novel Light Stabilizers-Guanine Analogs

The structural properties of DNA/RNA bases render them like sunscreens in natural system and thereby enhance our interest in using them for ultraviolet absorber development, which has rarely been investigated.In this paper, via extending theirπ-surfaces by the introduction of different substituted benzoyls-with electron donating group or electron withdrawing group, we synthesize eight guanine analogs including seven novel ones and one (A6) which is already existent. In contrast with absorption and emission data of guanine (ε=11142,9775), they possess wider ultraviolet absorbent range, higher molar extinction coefficient, especially A3 (21450) and A8 (22931), and lower fluorescence intensity. These results show that these guanine analogs exhibit significantly improve ultraviolet absorption capacity. Additionally, lower fluorescence intensity of analogs indicates that these modifications enhance their nonradiative ability which can decrease the probability of emitting quantum of energy that is presumably at a wavelength more or less harmful to the substrate. Furthermore, in accordance with the 1H NMR and FTIR results, we propose the possible mechanism of intramolecular hydrogen bond switching and proton-transfer of these analogs which is another effectively nonradiative way in consuming part of the harmful ultraviolet energy.Finally, based on rich chemical structures of these modified nucleobases, intensive researches on improving their ultraviolet absorption capacity and effectively nonradiative decay process in dissipating harmful ultraviolet light are in progress. These studies including the studies of intramolecular hydrogen bond switching and hydrogen atoms mobility in these analogs will not only accelerate the development of ultraviolet absorber but also other related biophysical and nonbiological applications in the basic sciences.