Correction of spectra for studying dye aggregates by resonance light scattering

Resonance light scattering (RLS), a phenomenon of abrupt enhancement of Rayleigh light scattering in close proximity to an absorption band, is easily detectable in solutions of strongly absorbing chromophores, which form large aggregates with strong π-electronic coupling among the chromophores. RLS spectra need to be corrected for the sensitivity of the spectrofluorimeter as well as for the effects of internal light filter. A method for correcting the measured RLS is described. It was shown by the method that addition of KCl induces formation of extended supramolecular aggregates (probably of H-type) of the anionic dye merocyanine 540 in water. The RLS spectra of a photosensitizer m-tetra(hydroxyphenyl)chlorin (Foscan®) indicate formation of J-aggregates of this dye in aqueous medium.