Synthesis and Optical Properties of Near Infrared Donor-ᴫ-Acceptor Fluorophores for Bioimaging Applications

Fluorophores containing donor, ᴫ linker, and acceptor units are gaining importance in the field of organic chemistry, especially showing fluorescence at near-infrared region. Herein, we report the synthesis and optical properties of donor-ᴫ-acceptor fluorophores containing indole, benzo[e]indole, and benzothiazole as donor units. The cyanoacetic acid/ malononitrile were used as acceptor units. The Vilsmeier Haack linker substituted with different functional groups such as hydrogen, t-butyl and phenyl at the 4th position was the as ᴫ-linker. The chlorine at meso-position was replaced with various nucleophiles such as piperidin-4-ylmethanol and pyridine-4-thiol. The fluorophores showed absorbance and emission maxima in NIR region (λabs =645 - 825 nm and λem = 784 - 828 nm) with and high molar extinction coefficients and photothermal stability. The fluorophores had Stokes shift of 6 – 143 nm and quantum yield of 7 - 20%. The biodistribution of the synthesized fluorophores were studied in collaboration with Dr. Hak Soo Choi