Raman excitation profiles of conjugated segments in solution

Journal Article · Sat Apr 01 04:00:00 EST 1995 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.51.8107· OSTI ID:6565780

Heller, C; Leising, G ^[1]; Godon, C; Lefrant, S ^[2]; Fischer, W; Stelzer, F ^[3]

---

1. Institut fuer Festkoerperphysik, Technische Universitaet Graz, Petersgasse 16, A-8010 Graz (Austria)
2. Laboratoire de Physique Cristalline, IMN, Institut des Materiaux de Nantes, Unite Mixte de Recherche CNRS/Universite de Nantes, No. 110, F-44072 Nantes (France)
3. Institut fuer Chemische Technologie organischer Stoffe, Technische Universitaet Graz, Stremayrgasse 16, A-8010 Graz (Austria)

We report on optical absorption and Raman scattering of [ital trans]-polyacetylene-polynorbornene diblock copolymers of varying block lengths in solution. Raman spectroscopy on the polyacetylene-type copolymer revealed well-separated peaks within the usually broad C=C stretching vibration band. These peaks show multimodal excitation profiles, and they are assigned to segments with 7, 9, 11, and 13 conjugated double bonds. The Raman frequencies of these peaks shift up to 5 cm[sup [minus]1] with excitation energy, which decreases with conjugation length. The overall dispersion of the vibration band with excitation energy is explained by the varying resonance conditions for the available conjugation lengths. Extrapolating the Raman frequencies towards infinite conjugation length, we estimate a limiting value of about 1440 cm[sup [minus]1] for the C=C stretching vibration. The dispersion of the gap energies with conjugation lengths gives a limiting value of about 1.50 eV for solutions in benzene or amorphous films. The molar distribution of conjugation lengths is calculated under the assumption that the contribution of a given conjugation length to the Raman spectrum is proportional to its concentration multiplied by an exponential function of the conjugation length [ital n][sup [alpha]], with [alpha] taken from the literature.

• OSTI ID: 6565780
• Journal Information: Physical Review, B: Condensed Matter; (United States), Journal Name: Physical Review, B: Condensed Matter; (United States) Vol. 51:13; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602* -- Other Materials-- Structure & Phase Studies
360606 -- Other Materials-- Physical Properties-- (1992-)
ABSORPTIVITY
COPOLYMERS
ENERGY-LEVEL DENSITY
MOLECULAR STRUCTURE
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PHYSICAL PROPERTIES
POLYMERS
RAMAN SPECTRA
SPECTRA