Tetsuya Gotoh

New organic non-linear optical crystals of benzylidene-aniline derivative

Abstract The benzylidene-aniline derivative with an electron-donating group at the 4-position and an electron-accepting group at the 4′-position has been suggested, by MO calculations, to have a small molecular dipole moment in spite of the large second-order hyperpolarizability, and hence to be a promising molecule in the search for new organic crystals with large second-order optical non-linearity. By modification of the molecule suggested, a series of crystals having high second-harmonic generation (SHG) activities have been discovered; one of them showed a larger powder SHG than 2-methyl-4-nitroaniline (MNA).

Exceptionally large third-order optical nonlinearity of the organic charge-transfer complex

The organic charge-transfer (CT) complexes that have a mixed-stack structure, in which organic electron donors and electron acceptors stack alternately plane to plane, such as perylene/tetracyanoethylene, showed larger third-harmonic generation than poly-(2,4-hexadiyn-1,6-diol-bis(p-toluenesulfonate), which is known as one of the best organic third-order nonlinear-optical materials. The component molecules of the complexes did not show much optical nonlinearity. The optical nonlinearity is large near the CT absorption-band wavelength along the CT axis, which means that the supramolecular electronic polarization along the CT axis is a novel and efficient origin of third-order optical nonlinearity.

Nonlinear optical effect of organic crystal heterostructures of benzylidene-aniline derivatives by two-step molecular-beam heteroepitaxy

A nonlinear optical waveguide with organic crystals based on 4′-nitrobenzyliden-3acetamino-4-methoxyaniline (MNBA) and its derivative was fabricated by organic molecular-beam epitaxy and operated as an electro-optic (EO) device. It has been proved that an EO coefficient r11 of MNBA significantly depends on the thickness of the 4′-nitrobenzyliden3-ethylcarbonylamino-4-methoxyaniline (MNBA–Et) homoepitaxial layer. Insertion of a thicker MNBA–Et homoepitaxial layer enlarges r11 of MNBA heteroepitaxial layer from 30 to more than 150 pm/V.

Dihedral rigid molecule in crystal engineering for optimized phase-matchable SHG: DNBB

It is important to control a polarization anisotropy, thus, a molecular alignment in obtaining such a crystal that can exhibit optimized phase-matchable second harmonic generation ( SHG ). Along with this view, we designed a novel dihedral rigid molecule which has two nitroaniline moieties rigidly connected each other through two adjacent sp3 carbons. We synthesized the molecules so designed and examined their crystals in SHG activities and phase-matching characteristics by a convenient powder method with a Nd:YAG laser. It has been found that one of crystals, namely, 3,9-dinitro-5a,6, ha, 12-tetrahydro[1,4]benzoxadino[3 ,2-bJ][1,4]- benzoxadine ( DNBB ) crystal manifests larger phase-matchable SHG than N-(4-nitrophenyl)-L-prolinol ( NPP ) crystal so far known as the typical efficient phase-matchable organic crystal. DNBB crystal has been shown to possess much improved material properties ; high thermal stability, distinguished hardness, insolubility to water, no sublimation, and high registivity to optical damage, for device applications in comparison with the crystals of p-nitroaniline derivatives reported so far.