On the search of new NLO materials with better mechanical properties, many researchers have focused on the small organic molecules having a large dipole moment and a chiral structure. These molecules are usually linked through the hydrogen bond 1-2.
Nonlinear optical (NLO) single crystals establish a variety of applications to perform functions like electro-optic switching, optical memory storage, frequency conversion, second harmonic generation and high energy lasers for inertial con?nement fusion research 3–7. Because of the large nonlinearities and optical threshold of organic materials, a wide range of such materials has been found by many researchers 8-10. In general, most of the organic molecules designed for nonlinear optical applications are the derivatives of an aromatic system substituted with donor and acceptor substituent 11-13. In recent years there have been extensive researches in the investigation of nonlinear optical crystals because of their potential applications in fabrication of optoelectronic devices 11–14. The organic crystals have large nonlinearity, but they have poor mechanical and thermal stability and are susceptible to damage during processing. Moreover, the growth of large size single crystal is difficult to grow for the fabrication of devices.
Inorganic crystals have excellent mechanical and thermal properties, but possess relatively modest optical nonlinearity because of the lack of extended pi-electron delocalization. Due to the above reasons, investigations have been made with semi-organic crystals which have combined properties of both organic and inorganic crystals and it is more suitable for device fabrication 15-19.