Morphology-dependent optical properties of substituted poly(p-phenylene-ethynylene)

X. M. Jiang(1), C. C. Wu(1), M. Wohlgenannt(1), W. Y. Huang(2), T. K. Kwei(2), Y. Okamoto(2) and Z. V. Vardeny(1)

(1) Department of Physics
University of Utah
Salt Lake City, Utah 84112
USA

(2) Polymer Research Institute
Polytechnic University
Brooklyn, New York 11201
USA

Two different batches of substituted poly(p-phenylene-ethynylene) [PPEs] were synthesized where the substituents dibutyl(a), di-2-ethylhexyl(d) were placed on the 2,5 positions of the phenyl rings. The PA spectrum of PPE(a) shows a polaron band at about 850cm-1. Whereas PPE(d) doesn't show any polaron absorption band. Visible photomodulation spectrum of PPE(a) has two main bands at T=10K around 1.25eV and 1.9eV plus a broad shoulder at 2.1eV. From PADMR spectrum we found that in PPE(a), the 1.9eV PA has spin 1/2, thus it is long-lived polaron generated in the polymer through photoexcitation, whereas the 1.25eV PA doesn't have any spin 1/2 resonance.