# Comparative Theoretical Evaluation of Hyperpolarizabilities of Push-Pull Polyenes and Polyynes. The Important Role of Configuration Mixing in the Excited States

Jain, Monika and Chandrasekhar, Jayaraman (1993) Comparative Theoretical Evaluation of Hyperpolarizabilities of Push-Pull Polyenes and Polyynes. The Important Role of Configuration Mixing in the Excited States. In: Journal of Physical Chemistry, 97 (16). pp. 4044-4049.

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## Abstract

The potential use of push-pull polyenes and polyynes for second harmonic generation has been compared on the basis of hyperpolarizabilities computed for a large number of model systems of the type $D(HC=CH)_nA$ and $D(C \equiv C)_n A$ (n=2-8, and D=$NH_2$, Br, or I; A=$NO_2$ or CN). Geometries optimized at the AM1 level were used in a CI calculation including single and pair excitations involving up to 193 configurations. The sum-over-states expression was used to obtain the $\beta$ values. While the trends in the computed $\beta$ are the same for the two series of compounds, the values are generally smaller and increase less rapidly with increasing $n$ for the polyynes. The results are interpreted in terms of the nature of the lowest excited states which contribute to $\beta$ in these systems. Mixing of in-plane and out-of-plane $\pi$ - $\pi$ * excited configurations reduces the contribution of the lower excited states to $\beta$ . Push-pull polyynes with higher $\beta$ values than the corresponding polyenes can be designed by the combined use of donor and acceptor groups such as I (or Br) and CN which can interact with both sets of orthogonal $\pi$ Mos.

Item Type: Journal Article Copyright of this article belongs to American Chemical Society. Division of Chemical Sciences > Organic Chemistry 25 Aug 2008 19 Sep 2010 04:29 http://eprints.iisc.ernet.in/id/eprint/7724