A Search for Some Wide-Range Tunable Dye Laser Systems Working on the 'Exciplex' Principle.

TLDR: In this article, a double proton exciplex mechanism was proposed for 9-aminoacridine, where the molecule is both a stronger acid and a stronger base in the excited state.

Abstract: : The 'exciplex' mechanism of radiation emission from a dye affords one means of producing a broad fluorescent spectrum without adding to the absorption spectrum. It relies on a change of equilibrium properties in the excited state compared with those of the ground state, and the fluorescence is not from the same chemical species absorbing the radiation. Such a system may show a considerable displacement of the fluorescence and absorption spectra so that the threshold input power for lasing may be reduced and the range of tuning can be extended. Also, by a careful selection of conditions, emissions from both the dye and the exciplex may appear, thereby permitting an even greater tuning range. Two mechanisms apply: the 'proton exciplex', which relates to changes in conventional acidity and basicity in the excited state; and the 'molecular exciplex', which relates to changes in electron-acceptor and electron-donor properties(i.e., changes in Lewis acidity and basicity). Wide tuning range (blue-violet to yellow-green, 122 nanometers) is reported for 4,8-dimethylumbelliferone. It is proposed that this dye operates by a double proton exciplex mechanism, wherein the molecule is both a stronger acid and a stronger base in the excited state. Peculiarities in the lasing action of 9-aminoacridine are discussed.