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The interaction of silver nanoparticles with four laser dyes, namely, LD-425, LD-489, LD-473, and LD-423, dispersed in methanol has been studied at room temperature by absorption and fluorescence spectroscopy. The silver nanoparticles were synthesized by chemical reduction and estimated size is 11 nm according to Mie theory. The changes in absorption spectrum of these dyes with the addition of silver nanoparticles suggest possible interaction with the silver nanoparticles. The magnitudes of the association constants are estimated using the Benesi–Hildebrand model. Fluorescence quenching has been observed for all the dyes with the addition of silver nanoparticles of different concentrations. The Stern–Volmer plots of fluorescence quenching in the case of LD-425 and LD-489 are found to be linear, suggesting the fluorescence quenching is because of the dynamic quenching process. But in the case of LD-473 and LD-423, the Stern–Volmer plots are nonlinear showing positive deviation and the fluorescence quenching in these dyes is because of static quenching processes. Also, it is found that the fluorescence quenching is not solely due to diffusion.

The effect of solvents of varying polarity and hydrogen bonding ability, solvent mixture and silver nanoparticles on the photophysical properties of a ketocyanine dye, 2,5-di[(E)-1-(4-diethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DEAPMC), is investigated at room temperature. Solvent effect is analyzed using Lippert-Mataga bulk polarity function, Reichardt's microscopic solvent polarity parameter, and Kamlet's and Catalan's multiple linear regression approaches. The spectral properties better follow Reichardt's microscopic solvent polarity parameter than the Lippert-Mataga bulk polarity function. This indicates that both general and specific solute-solvent interactions are operative. Kamlet's and Catalan's multiple linear regression approaches indicate that polarizability/dipolarity solvent influences are greater than hydrogen bond donor and hydrogen bond acceptor solvent influences. The solvatochromic correlations are used to estimate excited state dipole moment using the experimentally determined ground state dipole moment. The excited state dipole moment of the dye is found to be larger than its corresponding ground state dipole moment and ground and excited state dipole moments are not parallel, but subtend an angle of 77°. The absorption and emission spectra are modulated in the presence silver nanoparticles. The fluorescence of 2,5-DEAPMC is quenched by silver nanoparticles. The possible fluorescence quenching mechanisms are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of temperature on fluorescence quenching and emission characteristics of laser dyes (LD – 473) and (LD – 423) have been investigated in the temperature range 25°C - 65°C by steady state and transient methods. The fluorescence intensity of both dyes is quenched in the presence of quencher aniline at different temperatures. Stern-Volmer (S-V) plots are non-linear showing positive deviation. It has been found that dynamic quenching constant increases with temperature, whereas static quenching constant is independent of temperature. In both the dyes, Fluorescence emission intensity has decreased with increase in temperature and fluorescence band maxima is slightly shifted towards shorter wavelength. Further, fluorescence lifetime has decreased with increase in temperature for both the dyes. The possible deactivation mechanisms are discussed.

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