Two-dimensional fluorescence spectroscopy of resonance-stabilised radicals

Every chemical species has its own unique spectral fingerprint, which can be used to identify new molecules, or to elucidate the chemical environment. However, as the environment becomes more complex it becomes increasingly difficult to distinguish a single species, or to determine characteristics of the environment. Two-dimensional fluorescence spectroscopy allows intuitive identification of different molecules from a complex chemical environment, such as electrical discharges and flames [1]. In these environments, there are a large number of compounds, including transient reaction intermediates, both neutral and charged. Very “bright” and abundant species, such as C2 can dominate the optical spectrum, obscuring the spectral fingerprints of less abundant species. Using 2D fluorescence, however, the distinctive fingerprints of these weaker spectral features can be identified intuitively and unambiguously. We have used the 2D fluorescence technique to identify and characterise new molecules formed in electronic discharges of simple organic compounds. All of these transient species (vinylpropargyl, phenylpropargyl, indanyl, naphthylmethyl) are resonantly-stabilised radicals, which we hypothesize might also be intermediates in the combustion of these precursors. 2D fluorescence spectroscopy has also been used to identify two new electronic transitions involving a new valence electronic state in an archetypal compound (C2). The technique has also been used to separate and individually characterise structural isomers in the fluorescence spectrum of cis and trans-1-vinylpropargyl.