Styryl hemicyanine dyes with benzo[d]thiazolium and substituted N-phenylpiperazine end groups binding biological macromolecules

The potential of a series of styryl hemicyanine dyes as fluorescent bioprobes for biologically relevant macromolecules was investigated. The photophysical properties of the dyes were evaluated in the presence of nucleic acids, polysaccharides, and proteins. Pronounced fluorescence enhancement was observed upon interaction with human serum albumin (HSA), β-CDP, and lipopolysaccharide (LPS), with emission intensities increasing by up to 130-fold relative to the free dyes in solution. The observed fluorescence turn-on effect is attributed to restricted intramolecular rotation and stabilization of the locally excited state upon binding within hydrophobic or supramolecular environments. Geometry optimization at the M06-2X level and molecular docking studies were performed to elucidate the binding modes and revealed the key contribution of hydrophobic, electrostatic, and host–guest interactions to complex formation.