Squaraine-based near-infrared dye with bright fluorescence and solvatochromic property

We report a newly synthesized squaraine-based fluorescent dye (KSQ-2) with excellent and useful optical characteristics such as a sharp near-infrared (NIR) emission at 751 nm, an extremely high fluorescence quantum yield (phi = 0.56 in cyclohexane), and linear positive solvatochromic properties in the spectral region around 780 nm.