Ryoka Matsushima

Second-Harmonic Generation from Single Crystals of N-Substituted 4-Nitroanilines

Six N-substituted derivatives of 2-methyl-4-nitroaniline (MNA) and two N-substituted derivatives of 4-nitroaniline were synthesized and their physical and optical properties were examined in the search for nonlinear optical materials with a sufficiently large second harmonic (SH) activity and applicability to practical use. Some derivatives produced single crystals and their structures were determined by X-ray crystallography. The trends of the SH intensity of these materials could be qualitatively explained based on the b tensor (the effective molecular hyperpolarizability in the crystal). Amongst the derivatives examined in this investigation, N-benzyl-MNA showed the highest SH activity (up to twice that of MNA), thermostability and phase-matching ability.

Observation of Solitonlike Excitations in All-trans-β-Carotene Single Crystals

The crystal structure of all-trans-β-carotene was determined at 293 K. The space group determined in this investigation was consistent with that determined at 130 K by Senge et al. [Z. Naturforsch. C 47 (1992) 474]. Anisotropic displacements of lattice constants and molecular structures were observed upon raising the temperature from 130 K to 293 K. Photoinduced and time-resolved absorption spectroscopies were applied to all-trans-β-carotene single crystals. By exciting visible absorption bands of the crystals, we observed, for the first time, the photoinduced bleaching of infrared absorption bands. The bleaching typically showed a single-exponential recovery with a lifetime of ~10 ms, which shows that some kind of metastable state is produced by exciting the visible absorption bands of the crystals. Depending on the crystals, however, we observed stretched-exponential and power-law recoveries. By inference based on the results for trans-polyacetylene, the cause of the latter two recoveries was attributed to the recombination of solitonlike excitations. Semi-empirical and ab initio molecular orbital calculations indicated the presence of solitonlike excitations in finite polyenes.

Fabrication technique of a nonlinear optical structure using optical polymeric films by direct electron-beam irradiation

A simple fabrication technique of nonlinear optical structures for use with dye-doped polymer is described. Polymethylmethacrylate, U-100 polymer, and polystyrene were used as the host matrices to fabricate the nonlinear optical waveguide. The periodically poled nonlinear optical polymer structures and ridge-type channel structures were fabricated by direct electron-beam irradiation. The electron beam with 25 kV of energy was exposed directly onto the polymer films containing the nonlinear optical chromophores. We can also demonstrate the fabrication technique of the domain-inverted grating of dye-doped polystyrene film.

Molecular and Crystal Structures of 2-(All-trans-Retinylidene)-Indan-1,3-Dione

Molecular structures of a novel carotenoid analogue, 2-(all-trans-retinylidene)-indan-1,3-dione (RetInd), were determined in solution and in the crystalline state by 1H-NMR spectroscopy and by X-ray crystallography, respectively. They were compared with those of all-trans-retinal (Ret), a visual chromophore. Ret takes a 6s-cis configuration (a cis configuration around the C6–C7 single bond) that is usually found in carotenoid analogues that have β-end groups, both in solution and in the crystalline state. On the other hand, it was found that RetInd took a 6s-cis configuration in solution but it took a 6s-trans configuration in the crystalline state. Comparison of the crystallographic structures between Ret and RetInd lead us to the conclusion that a van der Waals attraction in polyene chains and steric repulsion between a cyclohexene and an indan-1,3-dione ring stabilized the 6s-trans configuration of RetInd in the crystalline state.

Second‐order nonlinearity of nonpoled polymeric thin films doped with pyrylium salts with blue window characteristics

A novel nonlinear organic ionic material, or pyrylium salt dye, is synthesized and doped in the polymer matrix. These guest‐host‐type polymer films, which have no absorption in the blue‐wavelength region, have second harmonic generation (SHG) activities without the electric‐field poling process. The nonlinear optical coefficient d33 is estimated as 1.10 pm/V at a 15 wt % of dye concentration. The nonlinearity is stable at room temperature and at 120 °C. The SHG device is fabricated using the nonpoled polymer film, and Cerenkov‐type phase‐matched SHG is observed.

SHG-active polymorphism of p-nitroaniline mixed with its N-alkyl derivatives

The second-harmonic generation (SHG) in each mixture of p-nitroaniline (p-NA) and its derivatives (n-methyl, n-ethyl, n-propyl, i-propyl, n-butyl, n-hexyl, dimethyl, phenyl, and diethyl-4-nitroaniline) was measured by the powder method with a Nd:YAG laser. Most of the mixtures having a typical eutectic phase diagram exhibited a high SHG intensity; in particular, the SHG activity of the p-NA/isopropyl-NA mixture was 1670 times higher than that of urea. This may be due to the crystal growth of noncentrosymmetrical polymorphism of p-NA on the surface of the isopropyl-NA. The crystal growth of the SHG-active polymorphism was accomplished by vacuum deposition on the isopropyl-NA substrate.

Second harmonic generation from organic nonlinear materials of N-alkyl-4-nitroaniline

Abstract We have systematically investigated a series of new nonlinear organic materials, N-alkyl-4-nitroaniline, by measuring the second harmonic generation (SHG) from powder samples of the five materials with the alkyl chain of different length. It is found that N-butyl-4-nitroaniline (BuNA) shows the largest SHG activity among them, and the SHG intensity measured is 14 times larger than that of urea, in contrast with no SHG activity of para-nitroaniline. It is also found that BuNA is a phase-matchable material and the SHG efficiency has a strong dependency upon the recrystallization solvent used for purifying the reaction product.

Second-harmonic generation from mixed crystals of p-nitroaniline

Second-harmonic (SH) activities of p-nitroaniline (pNA) crystallized in the presence of aromatic additives or impurities, have been measured by the SHG powder method with a 1064 nm Nd : YAG laser source; values were in the range 100–1000 × urea, depending on the additives and crystal-growth conditions. The SH-active crystals showed XRD patterns substantially different from that of the centrosymmetric pNA crystal, and were thermally unstable. The effects of foreign substances were discussed in terms of the control of crystal growth via an adsorption–inhibition mechanism.

Second-harmonic generation from mixed crystals of p-nitroaniline with substituted benzenes studied by the powder method

Second-harmonic generation (SHG) from mixed crystals of p-nitroaniline (p-NA) as guest and various substituted benzenes as host has been measured by the powder method with a 1064 nm YAG laser source. The SH intensities, which varied with crystallization conditions as well as host and mixing ratio, were as high as 100–189 × urea with p-dihydroxybenzene or p-dicyanobenzene as host. The SH intensity tends to increase with the size of the powdered crystals, implying a phase-matchable feature. The SHG activities were stable only at low (5 °C) temperature. It is speculated that epitaxial growth of p-NA crystals on the surface of host crystals would lead to an SHG-activity morphology.