Theory of optical transitions in conjugated polymers. I. Ideal systems
We describe a theory of linear optical transitions in conjugated polymers. The theory is based on three assumptions. The first is that the lowlying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, described by the FrenkelHolstein model. Second, we assume that the relevant parameter regime is ℏω ≪ J, i.e., the adiabatic regime, and thus the BornOppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the excitonpolaron wavefunction is essentially independent of the normal modes. Using these assumptions we derive an expression for an effective HuangRhys parameter for a chain (or chromophore) of N monomers, given by S(N) = S(1)/IPR, where S(1) is the HuangRhys parameter for an isolated monomer. IPR is the inverse participation ratio, defined by IPR = (∑{sub n}Ψ{sub n}{sup 4}){sup −1}, where Ψ{sub n} is the exciton centerofmass wavefunction. Since the IPR is proportional to the spread of the exciton centerofmass wavefunction, this is a key result, as it shows that S(N) decreases with chain length. As in molecules, in a polymer S(N) has two interpretations. First, ℏωS(N) is the relaxation energy of an excited state causedmore »
 Authors:

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 Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ (United Kingdom)
 (United Kingdom)
 Publication Date:
 OSTI Identifier:
 22310722
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 16; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; BORNOPPENHEIMER APPROXIMATION; CENTEROFMASS SYSTEM; COUPLING; DEGREES OF FREEDOM; EMISSION; EXCITATION; EXCITED STATES; EXCITONS; MOLECULES; MONOMERS; POLYMERS; WAVE FUNCTIONS