G‐Quartets, 4‐Way Junctions and Triple Helices but Not DNA Duplexes: Planarization of Twisted Push–Pull Flipper Probes by Surface Recognition Rather Than Physical Compression

Planarizable push–pull flipper probes have been introduced to image order and tension of membranes in living cells. In this report, we show that fluorescent flippers can also be planarized by chemical interactions on DNA architectures rather than by physical forces in biomembranes. Compared to fluorescence in water, the planarization on parallel cMyc G-quartets is characterized by a 100 nm red shift of the excitation maximum and a strong increase in fluorescence intensity. A coinciding 100 nm red shift of the emission maximum compared to planarized flippers in ordered membranes reveals that planarization occurs on the water-accessible surface rather than within the G-quartets. Less relevant for physical compression in the ground state in hydrophobic membranes, this functional relevance of flipper solvatochromism in the excited state, reflected by red shifts in emission rather than excitation, is unprecedented and introduces attractive dual sensing perspectives. With decreasing efficiency, flippers are also planarized by antiparallel hTel22 G-quartets, 4-way junctions and triple helices, while the aromatic surface of B-DNA duplexes is too small for strong enough π stacking. These remarkably consistent results expand the understanding of planarizable push–pull flipper probes and enable applications in new directions