570 nm/770 nm light-excited deep-red fluorescence switch based on dithienylethene derived from BF₂-curcuminoid

Developing dithienylethene (DTE)-based fluorescence switches triggered by biocompatible visible light has always been a long-term goal in view of their potential in numerous biological scenarios. However, their practical availability is severely limited by the short visible light (generally less than 500 nm) required for photocyclization, their inability to achieve red or near-infrared emission, and their short fluorescence lifetimes. Herein, we present a novel DTE derivative featuring a dimethylamine-functionalized BF₂-curcuminoid moiety (NBDC) by using an "acceptor synergistic conjugation system" strategy. The dimethylamine group not only enables a red shift in the absorption and emission wavelengths of the open isomer but also endows NBDC with unique acid/base-gated photochromism. As expected, as-prepared NBDC presents 570 nm/770 nm light-driven photochromic properties, red-emissive fluorescence, and thermally activated delayed fluorescence (TADF) switching in toluene. To our knowledge, this represents the first instance of a yellow-green- and NIR light-controlled red fluorescence DTE switch with the longer fluorescence lifetime. Specifically, NBDC, which shows weak photochromic activity in CHCl₃, demonstrates enhanced photochromic performance when gated by TFA/TEA. Ultimately, this non-toxic deep-red fluorescence switch has been successfully applied for photoswitchable imaging in vivo of living cells and zebrafish, further proving its versatility in life sciences.