STYRYLPYRIDINE AMINE EXCIPLEXES - SUBSTITUENT EFFECTS

Fluorescent exciplexes were observed between excited para-substituted trans-styrylpyridines (n-StP, n = 2,3,4 and X = CN, Cl, H, (CH3)2CH, CH3, CH3O) and three tertiary amines, (i.e. diisopropyl ethylamine, tributylamine and triethylamine) in n-hexane at room temperature. The exciplex emission for the 2-StP-amine system was extremely weak. The maximum fluorescence energies were correlated with the values of Rehm and Weller, except for those for the StP with cyano groups. There was better correlation when a stronger electron-donating amine was used. The quenching rate constants increase as DELTAG0 for electron transfer becomes more exergonic, except for the case of cyano derivatives. The exciplex fluorescent energies also showed a linear correlation with the Hammett sigma(p) constants, again except for the cyano derivatives. The calculated dipole moments for the styrylpyridine-amine exciplexes are larger than those for stilbene-amine exciplex systems.