Effect of Donor/Acceptor group position on the NLO properties of branched chain organic molecules

Abstract

The organic materials are the most investigated materials for their nonlinear optical properties in the past three decades. In this article the systematic investigation on the NLO properties of Donor/Acceptor substituted branched chain organic chromophores, chalcones, using semi empirical method is presented. The nonlinear optical molecular static first hyperpolarizability (β) was found to be larger for Donor/Acceptor group substituted at para position than that of substitution of Donor/Acceptor group at meta and ortho position. For designing NLO materials with high β it is recommended to make substitution of Donor/Acceptor group at para position rather than meta and ortho position. 1. INTRODUCTION Nonlinear optical (NLO) materials are attractive due to their applications in optical frequency converter, optical switch, optical parametric oscillators etc [1,2]. Initially inorganic materials were explored for the NLO properties and they are adopted in NLO applications [3]. Due to lesser magnitude of NLO coefficients and slow response of inorganics, researchers started to explored new materials for NLO applications. In the search for new materials for NLO applications organic materials were found to be attractive due to ultrafast response time, structural flexibility, thermal and chemical stability. Among the different types of organic materials chalcones are notable materials due to their transparency in blue region, good crystallizability, high second harmonic generation(SHG) efficiency, third order NLO properties, high laser damage threshold and thermal stability [4,5]. The chalcones molecules can be designed possess either D-π-A type structure or D-π-A-π-D type structure. The donor group can be placed at the either ends of the molecule to obtain D-π-A-π-D structure with carbonyl group acting as an acceptor group at the center of the molecule. In order to design D-π-A type push-pull system in chalcones it is