ISSN:
0887-6266
Keywords:
excimer
;
fluorescence
;
polyester
;
pyrene
;
rotational isomeric state model
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The ratio of excimer to monomer emission intensities, denoted by ID/IM, was measured for Py-COO(CH2CH2O)mCO — Py, where Py denotes the 1-pyrenyl group and m = 1-4, in solvents of different viscosity, η. Three different systems were used to change the viscosity of the medium: (a) Mixtures of methanol and ethylene glycol at 25°C, (b) linear aliphatic alcohols, H(CH2)nOH, where n =1-6, also at 25°C, and (c) ethylene glycol over the range 6.6-35°C. The ratio ID/IM decreases sharply as η increases, and the rate of the decrease in ID/IM is a function of m. Quantitatively, the dependence of ID/IM on η at high viscosity, i.e., the slope [d(ID/IM)/d(1/η)]∞, is larger in the present work than in another series of 1-pyrenyl diesters in which the flexible spacer is an oligomer of polyethylene, instead of an oligomer of polyoxyethylene. In the limit where η → ∞, the ratio ID/IM assumes its largest value in the bichromophoric compound with m = 2. However, as η decreases the compound with m = 3 becomes the one with the largest ID/IM. A complete rotational isomeric state analysis (for the compounds with m = 1-3) and a Monte Carlo simulation (for the compound m = 4) of the conformations of the diesters can rationalize the behavior of ID/IM in the high viscosity limit. ©1995 John Wiley & Sons, Inc.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/polb.1995.090330714
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