0000000000306571
AUTHOR
Susana Encinas
Intramolecular Interactions in the Triplet Excited States of Benzophenone–Thymine Dyads
Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 …
Singlet Excited-State Interactions in Naphthalene-Thymine Dyads
Two thymidine-derived nucleosides 1 and 2 were prepared by attaching a chiral naphthalene to the positions 5′ and 3′ of the sugar. The resulting dyads, which contain key substructures present in drugs and nucleic acids, exhibit different spatial arrangements (transoid or cisoid) of the fluorophore relative to the thymine unit. Emission measurements on these compounds in the presence of ROH molecules revealed a remarkable intramolecular fluorescence quenching for dyad 1. The obtained results are consistent with quenching of the singlet excited state of 1 by hydrogen-bond donor solvents. Thus, a physical deactivation process (vibronically induced internal conversion) would be the pathway resp…
Structure and Photochemical Behavior of the Cyclodextrin Inclusion Complexes of the Benzoylthiophene-Derived Drugs Tiaprofenic Acid (=5-Benzoyl-α-methylthiophene-2-acetic Acid) and Suprofen (=α-Methyl-4-(2-thienylcarbonyl)benzeneacetic Acid)
The effect of β-cyclodextrin (β-CD) on the excited-state reactivity of the two benzoylthiophene derivatives, tiaprofenic acid (TPA; 2) and suprofen (SPF; 3) in their carboxylate forms is studied. The presence of β-cyclodextrin does not affect the nature of the photoproduced transients and the photoproducts, but increases the photodegradation quantum yields of both drugs. The efficiency of the photodecarboxylation process is enhanced. This effect is rationalized in the light of the inclusion of 2 and 3 in the β-CD cavity, affecting the energy of the lowest excited states of the drugs. The structure of the complexes is determined by induced circular dichroism, and molecular-mechanics and dyna…