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1 December 1997 Photoexcitations in disubstituted acetylene polymers
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We have used a variety of optical techniques to study the photoexcitation dynamics in several disubstituted acetylene polymer thin films. We found that although these polymers have a degenerate ground state, as determined by iodine doping and C60 photodoping, they show strong photoluminescence in the blue/green spectral range with high quantum efficiency in thin films. The cw photo modulation spectrum contains a single photoinduced absorption (PA) band at 1.7 eV with monomolecular recombination kinetics with a lifetime of 25 ms. PA detected magnetic resonance (PADMR) shows that this PA band is related to spin 1/2 excitations, which therefore identifies it as due to neutral soliton antisoliton pairs (So, So), similar to the 1.35 eV PA band in t-(CH)x. No triplet PADMR signal was observed and we therefore conclude that triplet excitations are unstable in disubstituted acetylene polymers, even though singlet excitons relatively stable. We consider therefore a possible So photogeneration mechanism via singlet to triplet intersystem crossing, followed by triplet exciton decomposition into So So pairs. Also we detected polarons in a degenerate ground state polymer for the first time.
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Martin Liess, Ilarie I. Gontia, Toshio Masuda, Katsumi Yoshino, and Z. Valy Vardeny "Photoexcitations in disubstituted acetylene polymers", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997);

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