# Sudden polarization in interacting model $\pi$ systems: An exact study

Ramasesha, S and Albert, IDL (1990) Sudden polarization in interacting model $\pi$ systems: An exact study. In: Chemical Physics, 142 (3). pp. 395-402.

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## Abstract

The twisted excited state of polyenes has attracted much theoretical and experimental attention due to the postulate that it exhibits sudden polarization for twist angle $\theta = 90^°$. We examine this phenomenon in long chain polyenes using correlated model Hamiltonians. While the Hubbard model is employed to study this process as the correlations are gradually turned on, the Pariser-Parr-Pople (PPP) Hamiltonian is employed for a realistic study of long chain polyenes. Exact polarizabilities of the ground and excited states of polyenes with upto ten carbon atoms are calculated within the Hubbard and PPP models as a function of twist angle. We find that the dipole allowed excited states exhibit sudden polarization in all the cases. Besides, the $3^1A_g$ state in the covalent subspace which is a two-photon state also exhibits this phenomenon as it becomes degenerate with the dipole allowed excited state. It is suggested that photochemical processes involving zwitterionic intermediates should be possible through two-photon excitation to this covalent excited state.

Item Type: Journal Article Chemical Physics Elsevier Science B.V. Copyright of this article belongs to Elsevier Science B.V. polarization;Pariser-Parr-Pople;Hubbard;Hamiltonian Division of Chemical Sciences > Solid State & Structural Chemistry Unit 02 Jan 2008 19 Sep 2010 04:41 http://eprints.iisc.ac.in/id/eprint/12612