The use of tunable laser excitation to effect significant sharpening in the inhomogeneously-broadened fluorescence spectra of polycyclic aromatic hydrocarbons (PAHs) isolated in argon matrices at 15 K is reported. The broad-band-excited fluorescence spectra of most PAHs in solid argon exhibit complex multiplet structures assumed due to the location of individual PAH molecules in different types of discrete “sites” in the polycrystalline matrix. Under laser excitation, the fluorescence spectra of PAHs are strongly dependent on excitation wavelength. For most PAHs, there exists an “optimum” excitation wavelength, at which a “single-site” fluorescence spectrum comprising one intense feature having a bandwidth of SO cm−1 or less is obtained. The excitation and emission wavelengths for site-selection fluorescence of eleven PAHs matrix isolated in argon are tabulated, and the trade-offs implicit in choice of optimum excitation wavelengths for site-selection fluorometric detection of PAHs in multicomponent samples are addressed. Quantitative results for five constituents of a sixteen-component standard reference material exhibit excellent agreement with certified values.

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