Significant Fluorescence Enhancement of N,N-Dimethylaminobenzophenone after Embedding as a C-Nucleoside in DNA

N,N-dimethylaminobenzophenone (DMABP) represents an intramolecular donor--acceptor system resulting in luminescent properties that are highly sensitive to the local surrounding due to twisted intramolecular charge transfer (TICT). In this study, DMABP was covalently linked to a single (ss) or double-stranded (ds) DNA and studied by a combination of UV/Vis absorption and fluorescence spectroscopy as well as femtosecond pump-probe measurements. As a result of embedding DMABP into a DNA environment, a drastic increase of the fluorescence quantum yield (QY) by a factor of more than 100 was detected, as further evidenced by an increase of the lifetime of the relevant excited states from less than 10ps to more than 100ps. A direct comparison between the ss- and ds-DNA systems further demonstrates the high sensitivity to the surrounding area by means of a two-fold difference in QY and fluorescence lifetimes. As a consequence, the respective DNA moiety (stacking and folding knot) affects significantly the competition between radiationless relaxation processes and fluorescence by interacting with DMABP.