Estimation of ground and excited-state dipole moments of three symmetric carbocyanine dyes via the analysis of luminescence properties

The solvatochromic effect of solvents on the absorption and fluorescence spectra of three carbocyanine dyes, namely 1,1',3,3,3',3'-hexamethylindocarbocyanine chloride (HIC); 1,1',3,3,3',3'-hexamethylindodi carbocyanine iodide (HIDC); and 3,3'-diethyloxadicarbocyanine iodide (DODC), have been investigated. The experimental ground and excited-state dipole moments of the dyes have been estimated via the well-known models by Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, and the Dimroth-Reichardt's empirical model. The influence of the solvation effect on the luminescence quantum yields was also examined and a strong correlation between the luminescence quantum yield values and the solvent viscosity was established. The fluorescence signal enhancement sensitivities between dyes were compared based on the Forster-Hoffmann equation. DFT and TDDFT calculations at the CAM-B3LYP/6-31G(d,p) level of theory were performed for the analysis of the nature of the electron transitions in absorption and excitation processes. Six phases different in polarity were considered during these computations, namely the gas, toluene, chloroform, acetone, methanol, and water. Transition electron density plots, Mulliken atomic partial charges, and Mayer bond orders were used for the analysis of the redistribution of electron density upon excitation. The specific behavior of the dyes in the glycerol medium was interpreted via the analysis of non-covalent interactions between the dye and glycerol molecules in terms of the reduced density gradient method. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The solvatochromic effect of solvents on the absorption and fluorescence spectra of three carbocyanine dyes was investigated, estimating the experimental dipole moments and examining the influence of solvation effect on luminescence quantum yields. Comparison of fluorescence signal enhancement sensitivities and analysis of electron transitions in absorption and excitation processes were also conducted. Dyes' specific behavior in glycerol medium was interpreted via analysis of non-covalent interactions between the dye and glycerol molecules.