Selective detection of organic compounds via pump-probe laser photolytic fragmentation fluorescence spectrometry

The analytical applicability of molecular fluorescence spectrometry can be extended to virtually any nonfluorescent organic compound by converting that compound to small, emissive fragments via photofragmentation with intense laser radiation. This approach has been termed "Laser Photolytic Fragmentation Fluorescence Spectrometry" (LP-FFS) by our research group. In "pump-probe" LP-FFS, selective detection can be achieved by photolyzing all (or nearly all) of the constituents in a multicomponent sample with 193 nm radiation from the photolysis laser, while relying on the probe laser to produce differences in fragment fluorescence spectral patterns for the various sample constituents, differences in the relative fragment fluorescence signal intensities and differences for the dependence of the fragment fluorescence signal intensity upon the photolysis and probe laser fluence. In this work "pump-probe" LP-FFS was utilized in an attempt to discriminate C₃H₄O isomers; C₄H₆O isomers; C₄H₅N isomeric nitriles; allylamine (and its derivatives) and propargylamine; 1,3- and 1,4-pentadiene; 1-, 2- and 4- octene; and several sets of substituted aromatic compounds. The selective detection capabilities of "pump-probe" LP-FFS were attributed to alterations, by the probe laser, of the C₂ and/or CN fragment electronic state distributions generated by 193 nm photolysis of the parent compounds and/or the induction of photofragmentation by the probe laser of highly excited parent molecules and/or relatively large intermediate fragments formed by 193 nm photolysis of the parent compounds. Thus, the role of the probe laser in "pump-probe" LP-FFS experiments can best be described as complex in nature.