Vinyl-Pyridinium Triphenylamines: Novel Far-Red Emitters with High Photostability and Two-Photon Absorption Properties for Staining DNA

A series of mono‐, bis‐ and trisvinyl‐pyridinium triphenylamines (TP‐py) has been synthesised and evaluated for its one‐ and two‐photon absorption (2PA) induced‐fluorescence properties under biological conditions. Interestingly, these compounds are only weakly fluorescent in water, whereas their fluorescence emissions are strongly restored (exaltation factors of 20–100) upon binding to double‐stranded DNA. Additional measurements in glycerol indicate that the fluorescence increases are the result of immobilisation of the dyes in the DNA matrix, which inhibits rotational de‐excitation modes. This particular feature is especially remarkable in the case of the bis and tris derivatives (TP‐2 py, TP‐3 py), which each display a high affinity (Kd ∼μM) for dsDNA. TPIF measurements have shown that TP‐2 py and TP‐3 py each have a large 2PA cross section (δ up to 700 GM) both in glycerol and in the presence of DNA, which ranks them amongst the best 2PA biological fluorophores. Finally, one‐ and two‐photon confocal imaging in cells revealed that these compounds perform red staining (λem=660–680 nm) of nuclear DNA with excellent contrast. The remarkable optical properties of the TP‐py series, combined with their high photostability and their easy synthetic access, make these compounds extremely attractive for use in confocal and 2PA microscopy. From IR to red: Red light‐emitting vinyl‐triphenylamines have been synthesised and evaluated for their two‐photon absorption properties. These compounds proved to be excellent on/off probes that fluoresce only in the DNA matrix. Their large 2PA cross sections allow imaging of nuclear DNA with excellent contrast and brightness on IR excitation.