Generation of the Thymine Triplet State by Through-Bond Energy Transfer.

Benzophenone (BP) and drugs containing the BP chromophore, such as the non-steroidal anti-inflammatory drug ketoprofen, have been widely reported as DNA photosensitizers through triplet-triplet energy transfer (TTET). In the present work, a direct spectroscopic fingerprint for the formation of the thymine triplet (3 Thy*) by through-bond (TB) TTET from 3 BP* has been uncovered. This has been achieved in two new systems that have been designed and synthesized with one BP and one thymine (Thy) covalently linked to the two ends of the rigid skeleton of the natural bile acids cholic and lithocholic acid. The results shown here prove that it is possible to achieve triplet energy transfer to a Thy unit even when the photosensitizer is at a long (nonbonding) distance.