Heterocyclic quinol-type fluorophores.: Part 2.: Solid-state fluorescence enhancement behaviour of benzofurano[3,2-b]-naphthoquinol-type clathrate hosts upon inclusion of amine molecules

Novel benzofuranonaphthoquinol-type clathrate hosts, which exhibit fluorescence enhancement behaviour with a blue shift of the emission maximum upon formation of clathrates with amines, have been developed. The clathrate compounds are formed not only by cocrystallization from amine solutions but also by solid (host)-gas (amine vapour) contact. The time-dependent fluorescence excitation and emission spectral changes upon exposure to various amine vapours were measured for crystals and thin films of the host compound. The time-scale for the spectral changes has been greatly shortened by using thin films instead of crystals. The crystal structures of the clathrate compounds have been determined by X-ray analysis. On the basis of the spectral data and the crystal structures, the effects of the enclathrated guest on the solid-state photophysical properties of the clathrate compounds are discussed.