The photolysis of tetramethyluracil (TMU), in water and organic media, affords the cis-anti and trans-anti dimers as the major photoproducts, with the product distribution essentially independent of solvent. Quantum yields (φdf) are 0.015 in water and 0.004-0.007 in organic solvents. Quenching and sensitization studies indicate that the products are singlet derived, though the TMU triplet is detectable by energy transfer and can be cycloadded to vinyl acetate. The progressively increasing (stacking) association constants (thermal osmometry) for dimethyluracil (DMU), dimethylthymine (DMT), and TMU in water parallel the increasing degree of excited singlet state involvement in the photodimerization of these substrates in organic solvents. The role of trace aggregates in organic media is discussed.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry