Reorganization energies in organic π systems

• Published in: Journal of molecular structure. Theochem 1998-02, Vol.425 (1), p.155-159
• Main Authors: Larsson, Sven, Klimkāns, Agris, Rodriguez-Monge, Lucia, Duškesas, Grigorijus
• Format: Article
• Language: English
• Subjects: Ab initio; Bond order; Reorganization energy; Trapping; π systems
• ISSN: 0166-1280; 1872-7999
• DOI: 10.1016/S0166-1280(97)00216-9

Structural reorganization energies ( λ i ) for reduction are directly calculated by taking the difference in total energy between relaxed and unrelaxed systems. In organic π systems we find much smaller values of λ if correlation effects are taken into account. We also find that a ‘Hückel-SCF’ method due to Longuet-Higgins and Salem with bond length dependent couplings, similar to the Su-Schrieffer-Heeger model, gives results in good agreement with the (U)MP2 results where comparisons can be made. In linear polyenes ( C n H n + 2 ), λ i converges to 0.25–0.3 eV as n → ∞, where 0.08 eV arises from the CCC bond angles and the rest from bond lengths. The reason for the finite value of λ i as n → ∞ is that the added electron or hole localizes over a limited number of about 20 carbon atoms but this is not yet confirmed in ab initio calculations. In C 60 λ i is small (0.06 eV) since the bond order for LUMO is distributed on many bonds.