Probing of. pi. conjugation in trans -polyacetylene using near-infrared photoluminescence spectroscopy

Journal Article · Sat Jun 15 00:00:00 EDT 1991 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.43.14478· OSTI ID:5555924

Carter, P W ^[1]; Porter, J D ^[2]

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1. Department of Chemistry, University of California, Berkeley, Berkeley, California 94720 (USA)
2. Department of Chemistry, University of California, Berkeley, Berkeley, California 94720 (USA) Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)

Near-infrared photoluminescence from undoped {ital trans}-polyacetylene was attributed to emission from {ital cis} defects,'' structures composed of isolated bonds embedded within conjugated {ital trans}-(CH){sub {ital x}} segments. Spectra were found to be independent of residual transition-metal impurities in the polymer, but quantum efficiencies decreased with increasing concentrations of neutral defects and free carriers. The percolation limit for free carriers was achieved at about 30% overall {ital trans}-(CH){sub {ital x}}. The photoluminescence energy varied inversely with the length of the conjugated {ital cis} defects, with a different dependence than for polyenes in solution. Interchain interactions were found to be significant in the solid state, distorting bonding geometries and perturbing the electronic structure of the chains; we postulate they are essential for bulk conduction. Hueckel calculations yielded {beta}{sub 0}=1.08 eV for the {pi} interaction energy, predicting an energy of 0.39--0.43 eV for the {pi}-{pi}{sup *} transition of a typical bound neutral soliton. The band gap for {ital trans}-polyacetylene of infinite conjugation length was estimated to be 1.20 eV by extrapolation of the solid-state luminescence data. We conclude that thermally isomerized {ital trans}-polyacetylene is best described as being a three-dimensional ensemble of short, conjugated segments that are bounded and interconnected by defects and crosslinks. Mean segment lengths are probably less than 13 units.

• OSTI ID: 5555924
• Journal Information: Physical Review, B: Condensed Matter; (USA), Vol. 43:18; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
POLYACETYLENES
ELECTRONIC STRUCTURE
CARRIER DENSITY
CHAINS
CHEMICAL BONDS
DEFECTS
EXCITONS
HYBRIDIZATION
NEAR INFRARED RADIATION
PHOTOLUMINESCENCE
QUANTUM EFFICIENCY
RECOMBINATION
SPECTROSCOPY
EFFICIENCY
ELECTROMAGNETIC RADIATION
HYDROCARBONS
INFRARED RADIATION
LUMINESCENCE
ORGANIC COMPOUNDS
POLYENES
QUASI PARTICLES
RADIATIONS
400500* - Photochemistry
360603 - Materials- Properties