Development of Multi-component Emission System responding to Polar and Hydrogen-bonding Effects of Mixed Solvents

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The emission spectra of toluene (T)-triethylamine (TEA) systems were measured under conditions of steady-state illumination in some protic and aprotic solvent-THF mixtures. The fluorescence spectrum of the T-TEA system in THF could be separated into three component bands (band A at 279 nm (fluorescence of T), band B at 336 nm (fluorescence of TEA) and band C at 373 nm (emission from an intermolecular exciplex)). The intensities of bands B and C decreased with increasing solvent polarity. The decrease in the intensities of bands B and C is considered to be caused by the enhanced conversion of the exciplex to an ion-pair with increase in solvent polarity. The intensities of bands B and C also decreased owing to the hydrogen-bonding interaction between TEA and protic solvents, but in this case the intensity of band A increased. Acetonitrile only has a polar effect and trichloroacetic acid only has a hydrogen-bonding (or protonation) effect, while alcohols have both effects. The equilibrium constants for the formation of intermolecular hydrogen-bonded complexes of TEA with alcohols were estimated from the changes in the intensity of band A. The hydrogen-bonding and polar effects of alcohols on the intensities of bands B and C could be evaluated separately. The ratio of the hydrogen-bonding effect to the polar effect of alcohols was observed to increase with increasing vol% of alcohol.The emission systems of 4-Phenyl 1-N,N-dimethylaminopropane, naphthalene-TEA, and styrene-TEA were also investigated. In these systems the polar and hydrogen-bonding effects of protic solvents on the emission spectra could also be separately evaluated.