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Optical and magnetic properties of the exact PPP states of biphenyl

Ramasesha, S and Albert, IDL and Sinha, Bhabadyuti (1991) Optical and magnetic properties of the exact PPP states of biphenyl. In: Molecular Physics, 72 (3). pp. 537-547.

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The low-lying singlets and triplets of biphenyl are obtained exactly within the PPP model using the diagrammatic valence bond method. The energy gaps within the singlet manifold as well as the lowest singlet-triplet gap are found to be in good agreement with experimental results. The two weak absorptions between 4·1 and 4·2 eV reported experimentally are attributed to the two states lying below the optical gap that become weakly allowed on breaking electron-hole and inversion symmetries. The observed blue shift of the spectral lines, attributed to a change in dihedral angle, on going from crystalline to solution to vapour phase is also well reproduced within the PPP model. The bond orders show that the ground singlet state is benzenoidal while the dipole excited state as well as the lowest triplet state are quinonoidal and planar. Comparison with the experimental spin densities and the fine structure constants D and E in the triplet state point to slightly weaker correlations than assumed by the PPP model. The introduction of a 1-8 bond to mimic poly(paraphenylene)s gives an optical gap that is in good agreement with experiment.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Taylor and Francis Group.
Keywords: Valence-Bond Theory;Transition;Resonance;Matrices;Spectra.
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Depositing User: Ms Mary Ranjeetha
Date Deposited: 26 Nov 2010 07:03
Last Modified: 26 Nov 2010 07:03
URI: http://eprints.iisc.ac.in/id/eprint/34022

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