Dielectric enrichment of 1-(9-anthryl)-3-(4-N,N-dimethylaniline) propane in hexane-ethanol mixtures

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 h as a distinct emission spectrum that can be characterized as a single Gauss ian peak. We have studied preferential solvation of the ADMA SH state in bi nary hexane-ethanol mixtures by monitoring its peak emission energy. The re sults are analyzed with a theory of preferential solvation by dielectric en richment (Suppan, P. J. Chem, Sec., Faraday Trans. 1987, 83, 495). Our anal ysis demonstrates a significant influence of mixture dielectric nonideality on solvatochromism, and this effect can be misinterpreted as specific solv ent-solute interaction if it is not treated properly. We are able to separa te the influence of mixture nonideality from the influence of dielectric en richment, and conclude that specific interactions do not contribute to the observed solvatochromic shift in the ADMA-hexane-ethanol system. The analys is also indicates that solvent-solute interactions in this system can be ad equately described with a continuum model. We calculate the composition of the ADMA solvation shell and find that it is enriched ill ethanol by simila r to 50% over the bulk composition. ADMA is identified as an excellent prob e of dielectric enrichment in complex environments.