Crystal engineering, the ability to predict and control the packing of molecular building units in the solid state, has attracted much attention over the past three decades owing to its potential exploitation for the synthesis of technologically important materials. We present here the development of crystal-engineering strategies toward the synthesis of noncentrosymmetric infinite coordination networks for use as second-order nonlinear optical (NLO) materials. Work performed mainly in our laboratory has demonstrated that noncentrosymmetric solids based on infinite networks can be rationally synthesized by combining unsymmetrical bridging ligands and metal centers with well-defined coordination geometries. Specifically, coordination networks based on 3D diamondoid and 2D grid structures can be successfully engineered with a high degree of probability and predictability to crystallize in noncentrosymmetric space groups. We have also included noncentrosymmetric solids based on 1D chains and related helical structures for comparison.

Crystal engineering of NLO materials based on metal-organic coordination networks

Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Organic Optoelectronic Materials: Mechanisms and Applications

The ability of nonlinear optical materials to transmit, process and store information forms the basis of emerging optoelectronic and photonic technologies. Organic chromophore-containing polymers, in which the refractive index can be controlled by light or an electric field, are expected to play an important role.

Design and synthesis of chromophores and polymers for electro-optic and photorefractive applications

A new field of organic materials science that deals with amorphous molecular glasses has been opened up. In addition, amorphous molecular materials have constituted a new class of functional organic materials for use in various applications. This article is focused on the recent progress of studies on photo- and electroactive amorphous molecular materials, highlighting photochromic amorphous molecular materials, amorphous molecular resists, and amorphous molecular materials for use in devices such as organic EL devices. The molecular design concepts, syntheses, reactions, molecular and solid-state properties, functions, and device fabrication and performance are described.

Photo- and electroactive amorphous molecular materials—molecular design, syntheses, reactions, properties, and applications

Carbazole-containing polymers: synthesis, properties and applications

Polymeric photorefractive materials

We present experimental data that show that the greatly improved performance of a new class of photorefractive polymers [see Donckers , Opt. Lett.18, 1044 ( 1993)] is too large to be explained by the simple electro-optic photorefractive effect alone. In these materials a photoconducting polymer host is doped with a small concentration of a sensitizer and a large concentration of a nonlinear optical chromophore that has orientational mobility at ambient temperatures. We present a theoretical model for a new orientational enhancement mechanism in which both the birefringence of the sample and the electro-optic coefficient are periodically modulated by the space-charge field itself. The predictions of this model for the size of the enhancement (which is greater than an order of magnitude in diffraction efficiency), the polarization anisotropy between p-polarized and s-polarized readout, and the presence of index modulation at twice the grating wave vector are in good agreement with the measured properties. This orientational enhancement mechanism should be important in any system in which the nonlinear optical chromophores have sufficient orientational mobility and dipole moment so as to be oriented by the space-charge field itself.

Orientationally enhanced photorefractive effect in polymers

Two-beam-coupling gain coefficients exceeding the absorption coefficient are demonstrated for the first time to our knowledge in an organic photorefractive system. The material is based on the photoconducting polymer poly(N-vinylcarbazole), doped with the optically nonlinear chromophore 3-fluoro-4-N,N-diethylamino-β-nitrostyrene and sensitized for charge generation with 2,4,7-trinitro-9-fluorenone. The photorefractive performance is significantly better than that of any previously described organic. Diffraction efficiencies as large as 1% in a 125-μm sample, grating growth times of the order of 100 ms, and beam-coupling gain coefficients >10 cm−1 were observed at 647 nm (writing intensity of 1 W cm−2, applied field of 40 V μm−1).

Net two-beam-coupling gain in a polymeric photorefractive material.

The fullerene molecule C60 is shown to act as a useful sensitizer of a recently discovered photorefractive polymer. Measurements of the steady‐state diffraction efficiency, grating growth rate, and other photorefractive properties are presented as a function of C60 concentration, writing intensity, and applied electric field. The dc photoconductivity, grating growth rate, and steady‐state diffraction efficiency all increase by as much as a factor of 20 upon doping with up to 0.2 wt % C60. The sensitization appears to result from a small increase in the carrier generation efficiency and a larger increase in the useful optical absorption at the operating wavelength, 647 nm.

C60 sensitization of a photorefractive polymer

The photorefractive (PR) properties of guest–host polymer systems composed of the high-mobility charge-transporting host polymer poly(4-n-butoxyphenylethylsilane) (PBPES), a nonlinear dopant, and a sensitizer are characterized by four-wave mixing (FWM) and two-beam coupling (2BC). Steady-state diffraction efficiencies as high as 10−4 (λ = 753 nm, E0 = 16 V/μm; sample thickness, 175 μm) and rise times as short as 39 ms (λ = 647 nm, E0 = 11.4 V/μm, 1-W/cm2 intensity) are observed by FWM; to our knowledge this is the fastest response observed in a PR polymer to date. In addition, net 2BC gain was observed in one material combination The mobilities of PBPES and a mixture consisting of PBPES:Coumarin-153:C60 are measured, and the mobility of the latter is ~10−4 cm2/(V s) at E0 = 10 V/μm, a factor of 10 larger than that of the undoped polymer. The rate of grating growth is analyzed within a charge-generation-limited model. The evidence indicates that carrier mobility is not the limiting factor in the PR response of these materials.

S. M. Silence

Papers

Polymeric photorefractive materials

Orientationally enhanced photorefractive effect in polymers

Net two-beam-coupling gain in a polymeric photorefractive material.

C60 sensitization of a photorefractive polymer

Poly(silane)-based high-mobility photorefractive polymers