NIR-to-NIR two-photon bio-imaging using very bright tailored amino-heptamethines dyes

Amino-heptamethines are highly conjugated cationic dyes featuring electronic absorption in the red region and strong near-infrared (NIR) fluorescence. Unlike their parent chloro-heptamethine cyanines, the substitution of the central position of their polymethine skeleton with an amine confers them a high Stokes shift. This work reports the synthesis of amino-heptamethines and the investigation of their optical properties, including two-photon absorption in the NIR and short-wave infrared (SWIR) ranges, which has been overlooked for such chromophores so far. Their structures were tailored, introducing selected substitutuents on the indolenine moieties to modulate their hydrophobic/hydrophilic balance and investigate their potential as NIR-to-NIR two-photon probes for the bio-imaging of living cells.