The fluorescence lifetime and quantum yield f of isolated red polydiacetylene chains dispersed in their monomer single crystal matrix were measured between 10 and 100 K. increases up to 120 ps at 40 K, then rapidly decreases at higher T. f is a continuously decreasing function of T. The radiative lifetime r is proportional to ͱT in the whole T range studied. This is the expected behavior for a purely one-dimensional system without localization, a behavior which is not usually observed even in semiconductor quantum wires. An order of magnitude of the exciton effective mass m*Ϸ0.3 is inferred. The nonradiative lifetime nr is constant up to 50 K, then decreases exponentially, indicating the opening of a thermally activated decay channel.
Fluorescence of isolated polydiacetylene chains in their monomer crystal is studied. Two different resonant emissions are observed. One is the weak emission of the free exciton at 1.9 eV at 10 K. The other is a very narrow (1.5 meV FWHM) intense resonance emission line at 2.28 eV and originates from a small fraction of chains with different conformation. Instantaneous exciton selftrapping is inconsistent with these emissions. The large difference in quantum yields (factor .10 2 ) indicates that electronic relaxation of these chains is very sensitive to changes in chain conformation.[S0031-9007(98)06019-0]
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