Sensitized Liquid Phase Room Temperature Phosphorescence Applied to the Detection of Polychloronaphthalenes: The Influence of the Reversed Energy Transfer Reaction on the Linearity

Abstract

The detection of a series of polychloronaphthalenes (PCN's), i.e., mono-, di-, tri-, and tetra-substituted compounds, via sensitized room temperature phosphorescence of biacetyl in azeotropic acetonitrile/water is investigated. The detection limits are on the order of 10⁻⁸ to 10⁻⁹ M, except for 1,2,3-trichloro- and 1,2,3,4-tetrachloronaphthalene, and are comparable to those we obtained with fluorescence. Phosphorescence measurements at 77 K reveal that, with the exception of 1,2,3-trichloronaphthalene, for the tri- and tetra-substituted compounds the triplet state energies are lower than for biacetyl. Hence, for these PCN's the influence of the reversed energy transfer on the sensitized RTPL (room temperature phosphorescence in liquids) detection must be considered. On the basis of a theoretical treatment it is demonstrated that the reversed energy transfer manifests itself mainly via the linearity of the response. Furthermore, it is shown that the parameters needed for a quantitative interpretation of the results can be deduced from measurements of the direct phosphorescence of biacetyl.