Photolabile coumarins with improved efficiency through azetidinyl substitution

Azetidinyl substituents have been recently used to improve the fluorescence quantum yield of several classes of fluorophores. Herein, we demonstrate that other useful photochem. processes can be modulated using this strategy. In particular, we prepd. and measured the quantum yield of photorelease of a series of 7-azetidinyl-4-Me coumarin esters and compared it to their 7-diethylamino and julolidine-fused analogs. The efficiency of the photorelease reactions of the azetidinyl-substituted compds. was 2- to 5-fold higher than the corresponding diethylaminocoumarins. We investigated the origin of this effect in model fluorophores and in the photoactivatable esters, and found that H-bonding with the solvent seems to be the prominent deactivation channel inhibited upon substitution with an azetidinyl ring. We anticipate that this substitution strategy could be used to modulate other photochem. processes with applications in chem. biol., catalysis and materials science.