Method of Determination of Emission Properties of Very Weakly Emitting Species Ensuring Elimination of Emission of Impurities

Abstract

This paper describes a new type of spectrofluorimeter, composed of a high-performance liquid chromatography (HPLC) system directly connected to a fluorescence detector and an absorption photodiode array detector, designed for studying the emission of weakly emitting species. Procedures for measurements of emission spectra (ES), emission excitation spectra (EES), and quantum yields of emission (φE) for very weakly emitting systems (ΦE ≥ 10−7) have been proposed. The original methodical solution allows verification of whether the emission observed comes solely from the compound studied (and not from its impurities) or from some photochemical or thermal process taking place during measurements. Thanks to the use of this new type of spectrofluorimeter, it is possible to establish with a high probability that the dependence of the shape and position of the ES on the excitation wavelength and the differences between EES and absorptance spectra are due to photo-physical and/or photochemical properties of the compound studied and not due to the presence of emitting impurities. An especially interesting application of this method is to study the emission of species whose very weak emission is related to a very short lifetime as well as a low radiative rate constant. It is particularly suitable to the study of the emission properties of flexible molecules that can occur in a few conformers of different absorption and emission properties. The performance of the method is illustrated by the results of the emission studies carried out for Nα-acetyl-2-(uracil-5-yl)-L-tryptophan N-ethylamide.