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Issue 33, 2013
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Vibronic coupling density analysis for the chain-length dependence of reorganization energies in oligofluorenes: a comparative study with oligothiophenes

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Abstract

The vibronic coupling constants and reorganization energies of oligofluorenes OF(n) (n = 1–6) are calculated for their cationic states (hole transport). Those of oligothiophenes OT(2n) (n = 1–6) are also calculated for comparison. The vibronic coupling constants of OF(n) are smaller than those of OT(2n), and decrease with increasing n. For the elucidation of the small vibronic couplings of the oligofluorenes, the calculated vibronic coupling constants are analyzed on the basis of the concept of vibronic coupling density. The vibronic coupling density of OF(n) becomes small in the middle of the chain with increasing n because of the reduction in the electron-density difference between the neutral and cationic states. It is found that orbital relaxation plays a crucial role in the distribution of the electron-density difference. From the fragment molecular orbital analyses, the large orbital relaxation in OF(n) is found to originate from the small transfer integral between the fragment molecular orbitals. These findings led to a design principle for a carrier-transporting oligomer/polymer with small vibronic couplings, or small reorganization energy, as follows: the orbital interaction between the monomers should be small from the view of vibronic couplings.

Graphical abstract: Vibronic coupling density analysis for the chain-length dependence of reorganization energies in oligofluorenes: a comparative study with oligothiophenes

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Publication details

The article was received on 13 Apr 2013, accepted on 19 Jun 2013 and first published on 24 Jun 2013


Article type: Paper
DOI: 10.1039/C3CP51592C
Citation: Phys. Chem. Chem. Phys., 2013,15, 14006-14016
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    Vibronic coupling density analysis for the chain-length dependence of reorganization energies in oligofluorenes: a comparative study with oligothiophenes

    M. Uejima, T. Sato, K. Tanaka and H. Kaji, Phys. Chem. Chem. Phys., 2013, 15, 14006
    DOI: 10.1039/C3CP51592C

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