A co-registered molecular keypad lock for the generation of singlet oxygen

Abstract

A dithienylethene (DTE)-anthracene dicarboximide dyad was prepared by condensation of an amino-substituted photoswitch with 2,3-anthracenedicarboxylic anhydride. The asymmetrically substituted dyad also includes a pyridine moiety, which provides a handle for further post-synthetic modifications (e.g., the herein employed methylation). The methylated dyad can be photoswitched between the ring-open and ring-closed DTE forms in several cycles without noticeable fatigue, being the UV light-induced ring-closing much more efficient (Φ_o→c = 0.11) than the ring-opening at >550 nm light irradiation (Φ_c→o = 0.005). On the one hand, the ring-open form of the dyad shows significant blue fluorescence of the electronically-decoupled anthracene dicarboximide chromophore (λ_f = 427 nm, Φ_f = 0.19). However, this emission is quantitatively quenched by a highly efficient FRET process in the closed form of the dyad. On the other hand, the open form of the dyad also shows sufficient excited triplet-state population and subsequent sensitization of singlet-oxygen (¹O₂) formation (Φ_Δ = 0.21), which again is completely deactivated for the closed form of the DTE. The thus achieved dual light-control of ¹O₂ formation can be interpreted as a molecular keypad lock and provides an interesting additional layer of functionality of ¹O₂ photosensitizers (PSs). The concomitant observation of fluorescence enables the co-registered operation of the molecular device.