The fluorescence spectra of polystyrene solutions have been measured in various solvents. The ratio of the intensity ID of the excimer (short 1iving.excited dimer) band to the intensity IM of the monomer band depends on the solvent. The values extrapolated t o diluted solutions may be related to the average density of segments in a polymer molecule. Above concentrations of 0.1 g/100 ml, the ratio ID/IM increases with increasing concentration, and the peak position of the excimer band shifts to a longer wavelength.
ZUSAMMENFASSUNG:In verschiedenen Losungsmitteln wurden die Fluoreszenz-Spektren des Polystyrols gemessen. Das Verhaltnis der Intensitat ID der Excimer(kurzlebendes, angeregtes Dimeres)-Bande zu der Intensitat IM der Monomer-Bande hangt vom Losungsmittel ab. Die Werte konnen, extrapoliert nach kleinen Konzentrationen, zur durchschnittlichen Segmentdichte im Polymermolekul in Beziehung gesetzt werden. Oberhalb der Konzentration 0,l g/100 ml wachst das Verhaltnis ID/IM mit der Konzentration an, und die Excimer-Bande verschiebt sich nach langerer Wellenlange.
tert-butoxide in THE (room temperature, 8 h) dehydrohalogenated 8 to the novel and potentially useful tetraene 18 in excellent yield.The cycloadditions described in Table I may proceed in a stepwise manner via two discrete isobenzofuran intermediates or they may proceed via intermediate 2. That the intermediate, whatever it is, is extremely reactive is illustrated by entries 5,10, and 11, in which the dienophiles are simple acyclic or cyclic alkenes. The mass spectral results (which show that the bis-retro-Diels-Alder reaction of 1-adducts predominates strongly over the mono-retro-Diels-Alder), preliminary calculations17 (which show that 2 lies only about 30 kcal/mol above its known angular isomer 198), and the recent isolation of diradical 2018 (which is related to a more general class 21 to which 2 may belong) all encourage us to attempt to isolate arid/or trap 2 and analogues. These experiments are actively being pursued.Acknowledgment. We are indebted to the National Science Foundation (Grant CHE-87-12118) and the National Aeronautics and Space Administration (Grant NAG-3-670) for financial support of this research.(17) Carried out in collaboration with Professor James F. Harrison.
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