Effect of solvents, solvent mixture and silver nanoparticles on photophysical properties of a ketocyanine dye

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.