FLUORESCENCE EMISSION IN FLUID SOLUTION AND SUPERSONIC JET OF SYMMETRICAL BISBENZENES INCORPORATING A 3 MEMBERED FLEXIBLE CHAIN

Intramolecular excimer formation in symmetrical bichromophore compound s consisting of two benzene, anisole, and 2,6-dimethylbenzene groups c onnected by a highly flexible O-CH2-O chain has been evidenced from st eady state and time resolved fluorescence studies. The thermodynamic a nd kinetic parameters have been determined in methanol and for one of them in methylcyclohexane as a function of temperature. While the acti vation energy for the conformational change required for excimer forma tion is similar for both solvents, the preexponential factors deduced from Arrhenius plots appear to be larger in methanol than in methylcyc lohexane. The parallel investigation of fluorescence excitation and di spersed emission spectra of bis-p-methoxy-phenoxymethane in supersonic expansion has shown that two conformers coexist in the jet and that t he intrinsic barrier for excimer formation in the isolated molecule is larger than 2.3 kcal mol(-1). (C) 1998 Elsevier Science S.A.