Exciplex-Based Vapor/Liquid Visualization Systems Appropriate for Automotive Gasolines

This paper reports the development of exciplex-based vapor/liquid visualization systems based on exciplexes formed from tertiary amines and fluorine-substituted benzene and/or toluene. These systems are expected to be virtually coevaporative with solvents (fuels) boiling in the temperature range 70 to 110°C and thus are expected to track the vaporization of automotive gasoline effectively. A system consisting of 10% triethylamine/0.5% fluorobenzene/89.5% hexane should be coevaporative with a normal boiling point of 69°C. A system consisting of 10% n-propyldiethylamine/0.5% 4-fluorotoluene/89.5% isooctane should be coevaporative with a normal boiling point of approximately 100°C. Although the coevaporation of these systems is excellent, the exciplexes revert to varying extents to excited monomer at temperatures near 100°C. Thus there is considerable cross talk from the liquid into the vapor spectral region. The tertiary amines generally require excitation at wavelengths below 250 nm; the fluorobenzene or 4-fluorotoluene can be excited at 266 nm. Monomer emission peaks at 290 nm; exciplex emission peaks at 350 nm.