Design and Synthesis of a Dimethylindole Red Trimer: A New Light-Up Red-Emitting Fluorescent Probe for G-Quadruplexes

We present a zwitterionic fluorescent probe based on dimethylindole red (Dir) derivative (named Dir-Trimer), which was synthesized by organic amine covalently linking three red-emitting Dir units. The unique structure of Dir-Trimer with three zwitterionic units largely decreased its intrinsic fluorescence. Fluorescence experiments exhibit that Dir-Trimer selectively interacts with G-quadruplexes with large fluorescence enhancement and sensitivity. Further studies indicate that Dir-Trimer could visualize G-quadruplexes on cell level.