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Proceedings Paper

Quantum confinement effects on the ordering of the lowest-lying excited states in conjugated polymers
Author(s): Zhigang Shuai; Jean-Luc Bredas; Swapan K. Pati; S. Ramasesha
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Paper Abstract

The symmetrized density matrix renormalization group approach is applied within the extended Hubbard-Peierls model (with parameters U/t, V/t, and bond alternation (delta) ) to study the ordering of the lowest one-photon (11Bu-) and two-photon (21Ag+) states as well as the lowest-lying triplet states in 1D conjugated systems with chain lengths, N, up to N equals 80 sites. Three different types of crossovers are studied, as a function of U/t, (delta) , and N. The `U-crossover' and `(delta) -crossover' are examined for long chains, which provide a sharp contrast to the situation found previously for short chains. The `N-crossover', which only occurs for realistic intermediate correlation strength, illustrates the more localized nature of the 2Ag excitation relative to the 1Bu excitation. We also apply the quantum-chemical Pariser-Parr-Pople model with long-range Ohno potential to the polyene molecules. We find that the 2Ag state is always below the 1Bu state for chain lengths N equals 4 to 40. Most interestingly, the gap between 2Ag and 1Bu first increases for N up to 16, then levels off, and finally starts to decrease. Thus, extrapolations to long chain based on short polyene data are hazardous.

Paper Details

Date Published: 1 December 1997
PDF: 10 pages
Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997); doi: 10.1117/12.279282
Show Author Affiliations
Zhigang Shuai, Univ. de Mons-Hainaut (Belgium)
Jean-Luc Bredas, Univ. de Mons-Hainaut (Belgium)
Swapan K. Pati, Indian Institute of Science (India)
S. Ramasesha, Indian Institute of Science (India)

Published in SPIE Proceedings Vol. 3145:
Optical Probes of Conjugated Polymers
Z. Valy Vardeny; Lewis J. Rothberg, Editor(s)

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