Abstract
Nucleosidic diarylethenes (DAEs) are an emerging class of photochromes but have rarely been used in materials science. Here, we have developed doubly methylated DAEs derived from 2'-deoxyuridine with high thermal stability and fatigue resistance. These new photoswitches not only outperform their predecessors but also rival classical non-nucleosidic DAEs. To demonstrate the utility of these new DAEs, we have designed an all-optical excitonic switch consisting of two oligonucleotides: one strand containing a fluorogenic double-methylated 2'-deoxyuridine as a fluorescence donor and the other a tricyclic cytidine (tC) as acceptor, which together form a highly efficient conditional Förster-Resonance-Energy-Transfer (FRET) pair. The system was operated in liquid and solid phases and showed both strong distance- and orientation-dependent photochromic FRET. The superior ON/OFF contrast was maintained over up to 100 switching cycles, with no detectable fatigue.