-2-yl)ethenyl]-quinoxaline (PQX) is a promising fluorescent chromophore for the estimation of proteinbindingsitepolarity, due to its full-color solvatochromic fluorescence. A linear relationship was obtained between the peak emission wavenumber and E(T)(N) (normalized solvent polarity). The BSA bindingsitepolarity was estimated from the solvatochromic plot.