An Overview of Selective Amino acid Based NLO Crystals

An Overview of Selective Amino acid Based NLO Crystals Piperidine ring is one of the most recognizable structural entities among heterocyclic molecules [24]. Piperidine has a six-membered ring similar to cyclohexane with one methylene (CH2) replaced by secondary amino (NH) group. In 1853, Cahours, discovered the alkaloid piperine 1, which occurs in black pepper. Piperidine which was first isolated from piperine 1, inhibits human P-glycoprotein and CYP3A4. Thousands of piperidine compounds have been cited in clinical and preclinical studies. The synthesis of piperidine is easy, economic and less time consuming. The parent molecule is flexible in nature and hence various derivatives can be easily prepared by altering its substituent. In recent years, research efforts have been made in exploring novel organic materials for their potential use in a variety of devices. The materials which could produce green/blue laser light and could withstand high energy light radiation are of vital importance for their uses in devices. The basic understanding of organic nonlinear optical materials has been well established and extensive studies have been motivated by their wide range of potential applications. Optical second-harmonic generation (SHG) induced by an acoustical field was observed in several composites, both in bulk as well as in large sized nano crystallite samples. The effect is generally explained by a non-centrosymmetric spatial charge density distribution of photo carrier excitation under an external acoustical field due to the electrostriction (photo acoustical) effects. An organic molecule should possess large second-order hyperpolarizability to exhibit good non-linear optical properties. ОІ can be enha nced by increasing the intermolecular charge transfer interaction and by extending the size of conjugated system. The piperidine derivatives are well known for their outstanding green light transmittance much better than those observed in inorganic crystals and show conspicuous inclination to crystallize as non-centrosymmetric materials. The structural flexibility of organic compounds is an asset for materials with optimized second order NLO susceptibility, fast response and tailor-made flexibility. An innumerable of organic crystals are synthesized and grown as a part of this. One of the noticeable requirements for nonlinear crystal is that it should have excellent optical quality. For a device to flourish, it is vital that it should meet a number of criteria such as optical nonlinearity, chemical and thermal stability for life time system capability. Organic NLO materials are attracting a great deal of attention for possible use in optical devices because of their large optical nonlinearity, low cut-off wavelengths, fast response time and high thresholds for laser power. Most of the organic molecules show large nonlinear optical response, with the electron-donor and electron-acceptor groups located at the extreme of a system involving correlated and high delocalized П-electron states. A nonzero SHG behavior is present in centrosymmetric crystals if chiral molecules and circularly polarized light are used. It has been recognized that the two-photon optical properties of materials should be affected by the donor acceptor strength, the molecular structure, the conjugation length and the intermolecular charge transfer etc. The D-A conjugated oligomers usually have two types of molecular structures, such as asymmetrical D-A type and symmetrical D-A-D or A-D-A type. The optical properties of these oligomers can be easily tuned by the introduction of different donor or acceptor moieties. Apart from structural flexibility, which allows fine-tuning of chemical structures for the desired NLO properties, the organic materials are of great technological interest due to their low cost, ease of fabrication, handy integration into devices, low dielectric constant, high electro-optic coefficient value, and resistance to laser damages. Polar organic crystals, which form non-centrosymmetric crystal structures, are attracting much interest due to their potentially high nonlinearities and a rapid response in electro-optic effects that often surpass those on inorganic nonlinear optical materials.