Fluorescent probes based on styrylpyridinium derivatives: optical properties and membrane binding

Synthesis and optical properties of the new fluorescent probes — styrylpyridinium derivatives — have been described. Various derivatives of styrylpyridinium, e.g. dimethylamino- (DSP-6 and DSP-12), hydroxy- (HSP-14) and sulphoxy-hydroxy- (SHSP-12) compounds show a long-wave absorption band in ethanol at λ max abs 486,402 and 383 nm, respectively. The spectra are sensitive to solvent polarity exhibiting negative solvatochromism by 30–40 nm. Moreover, HSP-14 in aprotic solvents has another absorption band around 600 nm, characteristic of the base. The fluorescence of the probes covers the spectral region 480–650 nm, that of HSP-14 being generated only in the absorption region of the main band (402 nm). The absorption, excitation and fluorescence spectra of these compounds in a liposome suspension have been recorded. The binding of probes to liposomes leads to an increase in fluorescence quantum yield as compared to organic solvents (DSP) and water. Energy transfer in the HSP-14 → DSP-12 probe pair has been measured in a liposome suspension. The obtained results suggest that the chemical compounds in question may be useful as fluorescent probes. By varying substituents in the compounds, different spectral characteristics can be attained.