Photophysical behavior of oligoethylene glycols labeled with naphthalene carboxylate and phosphate esters

Abstract

The fluorescence spectra of tri- and tetraethylene glycol esterified with 2-(1-naphthyl)ethyl ethyl phosphate and 2-(1-naphthyl)ethyl 2-(ethoxy)ethyl phosphate were studied in dilute solutions of tetrahydrofuran (THF) and diethyl ether. They were compared with the fluorescence from tri- and tetraethylene glycol esterified with 1-naphthyl acetic acid. These compounds form intramolecular excimers. The extent of excimer formation is not extensive, but the relative amount of excimer emission from these compounds varies with the choice of solvent. Three synthetic intermediates to the phosphates, the 2-(1-naphthyl)ethyl N, N-diisopropylphosphoramidites of tri- and tetraethylene glycol and of 2-ethoxyethanol, were also examined. These compounds form intramolecular exciplexes. In THF, the relative amount of exciplex emission from the phosphoramidites follows the same trend as the carboxylate esters. In diethyl ether, the trend is different. Rates of fluorescence decay have been measured for these compounds. The results are discussed in terms of how information about the conformational and dynamic behavior of these molecules in solution can be obtained, and how the solvent can influence the relative amounts of excimer or exciplex fluorescence