The kinetics and mechanism of 9-methyl-anthracene (MA) fluorescence quenching by N,N-dimethylaniline (DMA) were studied in ethanol-toluene mixtures as a function of solvent molar composition. The inherent unimolecular decay rate of excited MA monomer exhibits negative deviation from the ideal behavior ranging from 1.0 x 108 s-1 (corresponding to pure toluene) to 1.6 x 108 s-1, (corresponding to pure ethanol). The quenching rate constant exhibits positive deviation from the ideal behavior ranging from 7.5 x 109 M-1s-1 to 8.7 x 109 M-1s-1. The high values of the quenching rate constant suggest that the reaction is diffusion-controlled thus the latter effect can be explained by the negative deviation of viscosity from the ideal behavior for the same solvent system. This conclusion was confirmed by the fact that the energy of activation of quenching coincides with that of viscosity. The quenching mechanism was determined from steady-state emission spectroscopy. In pure toluene, when the DMA concentration was 25 mM, in addition to the monomer spectrum structureless exciplex emission peak centered at 490 nm was detected. In pure ethanol under identical experimental conditions, the intensity of the exciplex peak was approximately ten times smaller. The relative quantum yield of exciplex luminescence is an approximately linear function of solvent molar composition. The observed effect may be attributed to ethanol’s higher dielectric constant which favors charge separation over the exciplex formation quenching mechanism. Additionally, the exciplex spectrum maximum shifts approximately 50 nm from pure toluene to pure ethanol in a linear fashion.

Temperature dependence and medium effects on methylanthracene fluorescence quenching by dimethylaniline

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.