Nonlinear optics molecules

LeBozec and co-workers have reported nonlinear behavior in a series ofterpyri-dyl and dipicolinic acid complexes, with further studies on these complexes by Maury and co-workers [83, 84]. Their research was on new molecular materials for optoelectronics, with studies based on octupolar nonlinear optical molecules showing that molecular quadratic hyperpolarizability values were strongly influenced by the symmetry of the complexes [85]. Other studies on organic-lanthanide complexes with nonlinear optics have also reported second- and third-harmonic generation behavior with simultaneous multiphoton absorption properties [50]. Such studies have shown the importance of coordination chemistry as a versatile tool in the design of nonlinear materials. 

Theoretical calculations have been made on stilbene which are relevant to photoisomerization dynamics. MNDO calculations of stilbene potential energy properties shows no evidence of a doubly excited "phantom" state but a singly excited state with adiabatic rotation around the central ethylene bond has only a small barrier on this path23T Calculations of dipole moments, optical spectra, and second order hyperpolarizability coefficients of some mono- and disubstituted stilbene molecules allows the design of useful nonlinear optical molecules 38. 

Photonics is playing an ever-increasing role in our modern information society. Photon is gradually replacing the electron, the elementary particle in electronics. Several hooks and reviews have appeared dealing with the theory of nonlinear optics and the structural characteristics and applications of nonlinear optical molecules and materials [1—18]. Tlie earliest nonlinear optical (NLO) effect discovered was the electro-optic (EO) effect. The linear EO coefficient defines the Pockel effect, discovered in 1906, while the quadratic (nonlinear) EO coefficient s,i relates to the Kerr effect, discovered 31 years later (1875). Truly, all-optical NLO effects were not discovered until the discovery of lasers. Second harmonic generation (SHG) was first observed in a single crystal of quartz by Franken et al. [1] in 1961. They frequency doubled the output of a ruby laser (694.3 nm) into the 383... 

The functions of bioniolecules, bioactive molecules, ferroelectronic crystalline liquids, organic nonlinear optical molecules and so on often arise from their chirality. This means that the development of methods for obtaining enantiopure compounds is very important. Many methods have been reported for obtaining enantiopure compounds and these can be roughly classified into two categories, enantioseparation and asymmetric synthesis. Each category is further classified into physical, chemical, and biological methods. 

Hulliger, J. Konig, 0. Hoss. R. Polar inclusion compounds of perhydrotriphenylene (PHTP) and efficient nonlinear optical molecules. Adv. Mater. 1995, 7, 719 721. 

One photorefractive polyimide 59 was formed by linking thee units, a substituted porphyrin (charge generator), 4-amino-4 -nitrostilbene derivative (the nonlinear optics molecule), and a charge transporting agent, pyromellitic dianhydride. This polyimide retains its nonlinear optical properties even after... 

Figure 8.9 Chemical structure of selected nonlinear optical molecules ...

For nonlinear optical molecules which do not possess the desired centrosymmetric crystallization, there are very potent methods to incorporate these chromophores into polymer hosts ( electric field poling ) (Singer et al., 1986,1987 Hubbard et al., 1989 Bjorklund et al., 1991), self-assembly of molecular layers (Li et al., 1990 Katz et al., 1991), and Langmuir-Blodgett assembly of films (Roberts et al 1990 Kajikawa et al., 1992 Marder et al., 1994). 

The most common nonlinear optical molecules, with a donor—Ji-system—acceptor structure are, as a rule, neutral in the ground state and become charged in the excited state by electron transfer, in contrast with 4 -[Methyl(diphenyl)phosphonio]biphenyl-4-yl triphenylborate (PBB), which has a high dipole moment in the ground state and a lower one in the excited state. The hyperpolarizability P of PBB is comparable to that of p-nitroaniline and fortunately PBB shows transparency above 400 nm. 

P. Pantelis. J. Hill, and P. L, Davies, Poled onpoly(vinylidcne fluoride-trifluoroethyloie) as a host for nonlinear optical molecules. Nonlinear Optical and Flectroactive Polymers, American Chemical Sodely, Washington. DC 1967,... 

Zyss, J-, Octupolar organic systems in quadratic nonlinear optics molecules and materials. Nonlinear Opt., 1, 1, 1991. 

A novel photocrosslinkable polymeric system has been developed for processing into films having stable second-order nonlinear optical properties. In the present system, polymers bearing photocrosslinkable chromophores, such as polyvinylcinnamate, are reacted with appropriately designed nonlinear optical molecules with the cinnamate or other photocrosslinkable functionalities for photocrosslinking at one, two or more points. The system can be poled and photocrosslinked in the poled state to yield a material with stable optical nonlinearity and large electro-optic coefficients. 

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