Hughie Fraser - Dalhousie University

Placement: University of Saskatchewan
Supervisor: Dr. Ron Steer

Photophysical Studies of some Azulene Derivatives

Absorption and emission spectra of various azulene derivatives (1-carboxaldehydeazulene, 1,3-dicarboxaldehydeazulene and diethyl 1,3-dipropenoateazulene) and diazulenes (3-(3-methylguaiazulene)guaiazulene (GMG), azulene-methyl-azulene (AMA), azulene-ethyl-azulene (AEA) and azulene-methyl-azulene-methyl-azulene (AMA)) have been measured in hydrocarbon and the analogous perfluorinated solvents. Fluorescence quantum yields were measured in the same solvents and as a function of temperature in low-temperature glasses. Perfluorinated solvents, which are very inert, increased the fluorescence quantum yield dramatically in the diazulenes suggesting that an excited state relaxation process such as hydrogen abstraction is not a feasible pathway in these solvents. Excited state lifetimes were also determined for some of these compounds using a time-correlated single photon counting method.

Of the diazulenes studied, GMG proved to be the most interesting. It had the highest fluorescence quantum yield of all the diazulenes studied (f_GMG = 7.99 x 10^-3 in perfluoro-1, 3-dimethylcyclohexane) and the fluorescence quantum yield increased by about a factor of five from 295 K to 77 K. The excited state decay exhibits two fluorescence lifetimes for GMG, which are solvent dependent. GMG was found to be photochemically active with a quantum yield of photodecomposition (f = 6.64 x 10^-3) nearly equal to that of the quantum yield of fluorescence. The interpretation of these data will be discussed.