Photophysical Properties of 2-Hydroxytryptanthrin Analog as a Near-Infrared Dye for Fluorescent Imaging

2-Hydroxytryptanthrin analog (2-(2-hydroxy-12-oxoindolo[2,1-b]quinazolin-6(12H)-ylidene)malononitrile, DCM-T2OH) was synthesized as a near-infrared (NIR) dye for fluorescent imaging. In high-polarity aprotic solvents (acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide), protic solvents (methanol and ethanol), and an aqueous solution containing 20% acetonitrile, both the absorption and fluorescence bands of DCM-T2OH were observed at the NIR region (650–900 nm), which is referred to as the “optical window” of cells and tissues.