4 Nitroaniline, second harmonic generation

The fundamentally important case p-nitroaniline (PNA), the high symmetry parent molecular unit of MNA, presents an excellent example for both experimental methodology and theoretical analysis. In the C 2 v symmetry for PNA and second harmonic generation, the measured principal component 3X is given by... 

It may not be a coincidence that nitroanilines have been a useful class of compounds for second harmonic generation (12-13). They naturally associate into polar arrays, which are manifested in their crystal structures. The important question is whether or not these polar arrays are likely to bias the resulting crystal structures to be acentric. Although we do not have large enough data sets to make a statistically convincing case, from a set of 32 primary and secondary nitroanilines and analogs, about 40% of their crystal structures are acentric. These compounds are all capable of... 

A novel approach in the materials chemistry of zeotypes uses their highly organized pore structure for the preparation of advanced materials with potentially interesting magnetic, optical or electronic properties [20]. An illustrative example is the work of Caro, Marlow and coworkers, who prepared a material that exhibits strong second harmonic generation (SHG), a phenomenon in non-linear optics (NLO) that is important for laser applications. The material is based on the aromatic molecule -nitroaniline (pNA) [30-32]. This polar molecule also exhibits strong hyperpolarizability, an... 

Fig. 3. Nanostructured composite of p-nitroaniline (pNA, top left) and AIPO4-5. Top right Anisotropic absorption of the composite The crystals appear yellow only when the electric field vector E of the linearly polarized light oscillates in the direction of the transition dipole moment of the blue absorption of the pNA molecules. When E and these dipole moments are perpendicular to each other, no absorption occurs in the visible region, so that the pNA/AlPO -S crystals appear colourless. Center Experiment to measure the second harmonic generation (SHG) of the pNA/AIP04-5 composite. Bottom right The measured SHG effect is a function of cos q>, where q> is the rotation angle of the polarization rotator. This result is in agreement with the expectation if it is assumed that the pNA molecules are aligned in the channels and their dipoles all possess the same orientation. After the work of Caro, Marlow and co-workers [30-32],...

Section 4.1.1 reviews second harmonic generation (SHG) for para-nitroaniline (PNA), Section 4.1.2 the polarizability and second hyperpolarizability of nitrogen and benzene, Section 4.1.3 the second hyperpolarizability of Cgo, Section 4.2 the excited state polarizability of pyrimidine and r-tetrazine. Section 4.3 three-photon absorption, and finally, in Section 4.5 the electronic g-tensor and the hyperfine coupling tensor are reviewed as examples of open shell DFT response properties. 

Optical processing systems are proposed based on relative intensity changes of second harmonic generation in sorbate complexes of p-nitroaniline and 2-methyl-p-nitroaniline in molecular sieve hosts [98]. Optical data storage would be one of a variety of potential electro-optical applications. In addition, molecular optical effects by third harmonic generation are suggested for optical data storage based on the possible formation of bistabilities for the local fields [65,99]. 

Second harmonic generation is an effect of the interaction of electromagnetic fields with materials having high molecular and bulk polarizability. After the interaction, the frequency of the output field is twice that of the incident field. Pure p-nitroaniline microcrystals do not generate second harmonic radiation when excited by a Nd-Yag laser [261]. The phenomenon was displayed by / -CD-p-nitroaniline microcrystals, as shown by the formation of noncentrosymmetric crystal structures. 

Phase-matched second harmonic generation in single crystal polymers was first observed in 2-methyl-4-nitroaniline substituted diacetylene polymers. Subsequently, a number of other diacetylene structures... 

Para-nitroaniline (pNA) is an organic chromophore that is often used as a tag in UV/Vis, Raman, and second-harmonic generation spectroscopies [86-91], pNA possesses electron donor amino group and electron acceptor nitro groups that give rise to a bright charge-... 

ABSTRACT. Second harmonic generation(S.H.G.) in inclusion complexes between dimethyl-cyclodextrin(dimethyl -CD) and nitroaniline derivatives occurs. This is due to the destruction of the centrosyimntric crystal structure in nitroaniline derivatives caused by forming inclusion complexes. S.H.G. intensity of dimethyl /-CD complex with N-methyl-nitroaniline is 5 5 times as large as that of urea. 

Sugihara, O., and Sasaki, K., Phase-matched second-harmonic generation in a 2-methyl-4-nitroaniline single-crystal waveguide combined structure of grating couplers and four-layer waveguide, J. Opt. Soc. Am. B, 9, 104-107 (1992). 

Watanabe, T., and Miyata, S., Effect of crystallization process on the second harmonic generation of poly(oxyethylene)/p-nitroaniline systems, Proc. SPIE, 1147, 101-107 (1989). 

Sasaki, K., Kinoshita, T., and Karasawa, N., Second harmonic generation of 2-methyl-4-nitroaniline by a neodymiumiyttrium aluminum garnet laser with a tapered slab-type optical waveguide, Appl. Phys. Lett., 45, 333, 1984. 

Pyroelectrics. In a crystal belonging to polar classes there is only one polar axis with a symmetry of the polar vector. These crystals are also piezoelectric, but, in addihon, manifest spontaneous polarization and all other polar properties. Such crystals are called pyroelectrics. An example is tourmaline having symmetry and shown in Fig. 13.1c. Pyroelectric crystals are also used in techniques as piezoelectrics and also as detectors of infrared light or a heat how. There are many organic pyroelectric crystals, e.g., p-nitroaniline, one of the best generators of the optical second harmonic. 

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