Influence of Silver Colloid Presence on Stilbazolium Merocyanine Emission

Abstract

Absorption, fluorescence emission, and fluorescence excitation spectra of stilbazolium merocyanine (1-(n-butyl)-4[(3,5-dimethoxy-4-oxocyclohexa-2,5-dienylidene) ethylidene]-1,4-dihydropyridyne) dye in water solution without and with colloidal silver addition were measured. In the presence of the colloid, besides the absorption band assigned to the protonated species of the dye (at 391 nm), an absorption band related to the free-base species appears at 490 nm. From the absorption and emission spectra, measured at various dye concentrations, follows that the aggregates are not effectively formed. Therefore, the long-wavelength absorption and fluorescence bands have to be related to some dye forms created by the solvatochromic effects. The fluorescence bands of the protonated and the free-base species are located at 559 nm and at about 630 nm, respectively. The shape of the long-wavelength band suggests the occurrence of more than one free-base form of the dye. At some dye and colloid concentrations, the global emission of the sample is enhanced as a result of silver addition. The increase in the emission yield of the dye could be partially due to not only the change in the concentrations of dye forms exhibiting various emission yields but is also due to the resonance surface plasmon effect. Because of the superposition of several effects, before the practical application of merocyanine as an indicator of metal presence in biological samples, its spectral properties in the system investigated should be established.

Influence of Silver Colloid on Fluorescein Spectral Properties

“…It is known that the position of the absorption of band of Ag colloid depends on the size and shape of particles [13]. As follows from the picture taken under an electron microscope of the colloids applied in our works [14], the colloid particles exhibit different sizes. As a result, broad flat absorption band in the region 350-600 nm (Fig.…”

“…The colloid absorption is much lower than that of fluorescein (Fig. 2), also the light scattering on the colloid particles in used experimental configuration can be neglected in analysis of the fluorescence spectra [6,14].…”