Noncentrosymmetric structures, strategies

STRATEGIES TO OBTAIN NONCENTROSYMMETRIC STRUCTURES FOR QUADRATIC NLO APPLICATIONS... 

In the area of surface science, a GA has been applied [105] for the direct phasing of surface diffraction data as part of a strategy to determine surface structure using direct methods. The method has been applied to both centrosymmetric and noncentrosymmetric two-dimensional structures. 

In this chapter we report on some novel strategies that have been pursued to obtain efficient second-order nonlinear molecules starting from the well-known phthalocyanines. In principle, these planar centrosymmetric molecules do not present second-order activity and have been extensively studied for third-order applications. In order to induce asymmetry, two main approaches have been followed a) peripheral substitution of the macrocycle with donor and acceptor groups and b) structural modifications of the Pc core to reduce the symmetry, the resulting-noncentrosymmetric compounds (i.e. subphthalocyanines) presenting variable degrees of dipolarity/octupolarity in the nonlinear response. 

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