Second-harmonic generation and electronic structure of polymethineimines: a theoretical study

Albert, IDL and Das, Puspendu K and Ramasesha, S (1991) Second-harmonic generation and electronic structure of polymethineimines: a theoretical study. In: Chemical Physics Letters, 176 (2). pp. 217-224.

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Abstract

The second-harmonic-generation (SHG) coefficients and properties of low-lying electronic states in polyrnethineimines $(-CH=N-)_x$, up to x= 5 are calculated exactly within the PPP (Pariser-Parr-Pople) Hamiltonian. The $sp^2$ hybridized nitrogenatom parameters for the PPP model are taken from the literature, tested, and found to be satisfactory on pyridine, pyrazine, pyrimidine and s-triazine for which experimental optical gaps are known. The polymethineimines show an optical gapcomparable to that of polyenes and the extrapolated single-strand gap for the infinite polymer is 2.67 eV, slightly smaller than that obtained for polyacetylene. The SHG coefficients in polymethineimines arecomparable to that of the isoelectronic push-pull polyenes with moderately strong electron donors and acceptors. These molecules show a strong length dependence of the SHG coefficient which varies as $L^3^.^0^4$. These results are also valid for the mixed-stack donor-acceptor systems at half-filling.

Item Type:	Journal Article
Additional Information:	Copyright of this article belongs to Elsevier
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	26 Jun 2007
Last Modified:	02 Nov 2010 11:09
URI:	http://eprints.iisc.ernet.in/id/eprint/11266

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