Photochemical reactions on the synthetic polymers containing thymine bases

Photodimerizations of N-2-isobutyloxyethyl thymine (T-M), bis[2-(5-methyl-1-pyrimidinyl)ethyl]glutarate (T-T), poly-N-2-methacryloyloxethyl thymine (P-MAOT) and poly-N-2-acryloyloxyethyl thymine (P-AOT) were studied in dimethylformamide solution. Quantum efficiencies of intramolecular photodimerizations were determined to be 0.0012 for T-T, 0.0084 for P-MAOT and 0.010 for P-AOT. In the case of T-M, however, intermolecular photodimerization did not occur under the reaction condition used. Quenching studies by using isoprene suggest that the photodimerization of T-T occurs predominantly through an excited triplet state, while that of P-MAOT and P-AOT occur through both singlet and triplet states. For the effect of adding model compounds containing adenine bases on this reaction, adenine derivatives acts as an inhibitor against this reaction by quenching the excited singlet state of thymine. The photodimers of T-T, P-MAOT and P-AOT were concluded to be two syn-fused cyclobutane- type dimers (cis-syn and trans-syn).