Quantum confinement effects on the ordering of the lowest-lying excited states in conjugated polymers

Zhigang Shuai; Jean-Luc Bredas; Swapan K. Pati; S. Ramasesha

doi:10.1117/12.279282

1 December 1997 Quantum confinement effects on the ordering of the lowest-lying excited states in conjugated polymers

Zhigang Shuai, Jean-Luc Bredas, Swapan K. Pati, S. Ramasesha

Proceedings Volume 3145, Optical Probes of Conjugated Polymers; (1997) https://doi.org/10.1117/12.279282
Event: Optical Science, Engineering and Instrumentation '97, 1997, San Diego, CA, United States

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 (1¹B_u^-) and two-photon (2¹A_g⁺) 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 2A_g excitation relative to the 1B_u excitation. We also apply the quantum-chemical Pariser-Parr-Pople model with long-range Ohno potential to the polyene molecules. We find that the 2A_g state is always below the 1B_u state for chain lengths N equals 4 to 40. Most interestingly, the gap between 2A_g and 1B_u 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.

Citation Download Citation

Zhigang Shuai, Jean-Luc Bredas, Swapan K. Pati, and S. Ramasesha "Quantum confinement effects on the ordering of the lowest-lying excited states in conjugated polymers", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997); https://doi.org/10.1117/12.279282

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