The Use of Structure Analysis Methods in Combination with Semi-empirical Quantum-Chemical Calculations for the Estimation of Quadratic Nonlinear Optical Coefficients of Organic Crystals

An effective search for new organic crystals for prospective use in nonlinear optical (NLO) applications requires quantitative and fast experimental determination of their NLO properties at a molecular level. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by X-ray methods, is a time-consuming and sometimes impossible task. Single crystals of a considerably smaller size may be effectively used for complete structural analysis by electron diffraction combined with simulation methods. When the crystal structure of a given compound is known, its NLO properties may be estimated using quantum-chemical methods for calculation of the molecular nonlinearity tensor and the relationships between its components and the macroscopic coefficients of the crystalline nonlinearity tensor. In the present work, the semiempirical PM-3 method was employed for this aim

Theoretical and experimental investigation of electric field induced second harmonic generation in tetrathia 7 helicenes

In this paper, we report the first systematic experimental and theoretical investigation of the electric field induced second harmonic response of some tetrathia[7]helicene-based NLOphores. We studied six model compounds carrying the NO2, CH=CHCN, and COCF3 units as accepting groups on both the terminal thiophene positions as well as on the central benzene ring of the helicene backbone. These groups, known to be of medium and medium-strong accepting strength, allow tuning of both the electronic and structural properties of the helicenes studied. This experimental/theoretical study should set a milestone in addressing new structure-properties relationship of this class of nonconventional chiral chromophores able to show second order as well as third order NLO phenomena