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1 December 1997 Tuning of fluorescence in films and nanoparticles of oligo-phenylenevinylenes
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Oligo-phenylenevinylenes (OPV) with a series of distance controlling, electron donating, and/or electron withdrawing substituents are deposited from vapor phase and solution as ultrathin films or nanoparticles with diameters of 20 - 200 nm. In some cases the systems are doped at levels of 10-5 - 10-3 with energy accepting OPV's of longer chainlengths. Absorption and fluorescence spectra, steady-state and time-resolved anisotropies, radiative and nonradiative deactivation rates of these systems are investigated and compared to the corresponding properties in dilute solutions. Fluorescence yields of the parent oligomers and their alkyl or oxyalkyl derivatives are high in solution with an `infinite' chain limit of (Phi) F approximately equals 0.5 and an upper radiative rate constant limit of kr(infinity ) equals (1 +/- 0.3) (DOT) 109 s-1. Yields and kr decrease strongly in films and nanoparticles because of H-aggregate formation. However, doping with fluorescent acceptors can increase the yields up to (Phi) F yields 0.7. Introduction of electron withdrawing -CN and -SO2CF3 substituents reduces (Phi) F in low viscous dilute solutions almost to zero. High viscosities and condensation to solid phases will rise the yields up to (Phi) F yields 0.6 because of suppression of nonradiative torsional deactivation and formation of J- aggregates with high kr.
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Dieter Oelkrug, Alfred Tompert, Johannes Gierschner, Hans-Joachim Egelhaaf, Michael Hanack, Michael Hohloch, and Elke Steinhuber "Tuning of fluorescence in films and nanoparticles of oligo-phenylenevinylenes", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997);


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