# Optical nonlinearities in symmetric cyanine dyes and related systems

Albert, IDL and Das, PK and Ramasesha, S (1993) Optical nonlinearities in symmetric cyanine dyes and related systems. In: Journal of the Optical Society of America B, 10 (8). pp. 1365-1371.

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## Abstract

First- and third-order dynamic polarizabilities and hyperpolarizabilities of aza-cyanine and symmetric cyanine dyes have been computed exactly within the correlated Pariser-Parr-Pople model defined over the $\pi$ framework.The exact nonlinearities of the model have been compared with those of polyenic systems. It is found that for the same chain length the cyanine dyes have the largest linear $(\alpha_{ij})$ and third-order nonlinear $(\gamma_{ijkl})$ coefficients among the carbon backbone systems. Azacyanine dyes have intermediate polarizabilities, and the polymethineimines have the lowest. This is explained by the presence of terminal nitrogen-atom conjugation in the cyanine dyes, resulting in the lowering of optical gaps, which in turn brings the system close to resonance and results in larger linear and nonlinear coefficients. Chain length and frequency dependencies of $\alpha\ and$\hspace{3}\gamma\ of these systems are also reported.

Item Type: Journal Article Copyright of this article belongs to Optical Society of America. Division of Chemical Sciences > Solid State & Structural Chemistry UnitDivision of Chemical Sciences > Inorganic & Physical Chemistry 20 Nov 2006 27 Aug 2008 12:22 http://eprints.iisc.ernet.in/id/eprint/8565