Date of Award
Doctor of Philosophy
Physics and Astronomy
Conductivity, optical properties including visible and infrared (IR) absorption and photoluminescence (PL), and magnetic resonance properties including electron spin resonance (ESR) and optically detected magnetic resonance (ODMR) have been studied in polydiethynylsilanes (PDES) and poly(2,5-dibutoxyparaphenyleneacetylene) (PDBOPA), which were recently synthesized by Dr. T. J. Barton's group at the Ames Laboratory. PDES and PDBOPA blend and PDBOPA-based electroluminescent preliminary diodes which were fabricated by the author were also explored;The undoped one-dimensional gap of PDES polymers, which have average molecular weight from ~2 x 10[superscript]5 to 1 x 10[superscript]6, is 2.0 eV in both films and solutions; photoluminescence is barely observed. I[subscript]2 doping induces a single absorption band at ~1.05 eV in solutions and lightly doped films, but another at ~0.55 eV in heavily doped films. Both are correlated with strong IR-active vibrations associated with known lines in Raman scattering. The doping-induced ESR of the solutions is linear in the 1.05-eV peak, but only ~2% of the carriers yield an ESR, which is motionally narrowed. No double modulation light-induced ESR is detected. The results are discussed in relation to solitons, polarons, bipolarons, and A-B solitons;PDBOPA with average molecular weight ~5 x 10[superscript]4 is somehow passive to I[subscript]2 doping. Exposure to I[subscript]2 vapor at ~80°C increases the conductivity to ~5 x 10[superscript]-3 S/cm, but the I[subscript]2 rapidly evolves from the film at room temperature. The absorption onsets at 2.53 eV and peaks at 2.81 eV. The 2.71 eV-excited photoluminescence (PL) peaks at ~2.0 eV in films and solutions. In all cases, it is very intense and largely structureless. Three PL-enhancing ODMR features are observed: (i) a strong narrow (~15 G wide) resonance at g = 2.0025, attributed to intrachain polaron recombination; (ii) a ~1.2 kG wide triplet exciton powder pattern around g ~ 2, and (iii) the [delta]m[subscript] s = 2 transitions of these excitons at g ≅ 4.07. The results are discussed in relation to conformational defects resulting from the near cylindrical symmetry of the backbone acetylene units;The improving optical properties of dilute PDBOPA blend over pure PDBOPA including the strong enhancement of the PL quantum yield, reduced photoinduced degradation, a large blue shift of the PL peak and a partially resolved vibronic structure in the PL spectrum are discussed within the framework of dynamics of photo-excitation and decay. The PDBOPA based electroluminescent diodes have been successfully fabricated for the first time, although the quantum yield was low. Suggestions for improvements are briefly discussed. ftn*DOE Report IS-T-1559. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Ni, Qing-Xiao, "Electrical, optical and magnetic resonance studies of novel [pi]-conjugated polymers " (1992). Retrospective Theses and Dissertations. 9939.