Dielectric Enrichment of 1-(9-Anthryl)-3-(4-N,N-dimethylaniline) Propane in Hexane−Ethanol Mixtures

Abstract

1-(9-Anthryl)-3-(4-N,N-dimethylaniline) propane (ADMA) is known to form an emissive “sandwich heteroexcimer” (SH) in the excited state. The SH state has a distinct emission spectrum that can be characterized as a single Gaussian peak. We have studied preferential solvation of the ADMA SH state in binary hexane−ethanol mixtures by monitoring its peak emission energy. The results are analyzed with a theory of preferential solvation by dielectric enrichment (Suppan, P. J. Chem. Soc., Faraday Trans. 1987, 83, 495). Our analysis demonstrates a significant influence of mixture dielectric nonideality on solvatochromism, and this effect can be misinterpreted as specific solvent−solute interaction if it is not treated properly. We are able to separate the influence of mixture nonideality from the influence of dielectric enrichment, and conclude that specific interactions do not contribute to the observed solvatochromic shift in the ADMA−hexane−ethanol system. The analysis also indicates that solvent−solute interactions in this system can be adequately described with a continuum model. We calculate the composition of the ADMA solvation shell and find that it is enriched in ethanol by ∼50% over the bulk composition. ADMA is identified as an excellent probe of dielectric enrichment in complex environments.