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A series of symmetric derivatives of 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran (DCM laser dye) has been synthesized, and the nonlinear optical properties and thermal decomposition temperatures of each of the chromophores has been measured. The symmetric chromophores all have larger hyperpolarizabilities than one would expect based on their absorption maxima. Estimations of their oscillator strengths based upon UV/vis spectra are all well above 1.0. It is proposed that these compounds possess two excited electronic states close to each other in energy, both contributing to the hyperpolarizability in an additive fashion. Electro-optical absorption spectroscopy data and semiempirical calculations on a model compound support this hypothesis. The implications of these results with regard to the tradeoff between nonlinearity and transparency are discussed. The large dipole moments and high decomposition temperatures of these chromophores make them attractive candidates for use in electro-optic polymers.

The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties.

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We describe here the preparation and characterization of the first processible nonlinear optical (NLO) polyimide where the chromophore is not incorporated using a flexible tether functionality. The polymer has a very high glass temperature and shows exceptional thermal and chemical stability. Poled samples also show outstanding orientational stability, consistent in part with the high glass transition temperature.

It is demonstrated that the microscopic mechanism of the photorefractive (PR) effect in organic composites with low glass transition temperatures involves the formation of refractive index gratings through a space-charge field-modulated Kerr effect. A tensorial formulation of the macroscopic aspects of the PR Kerr effect and its microscopic interpretation is presented. The second-order dipole orientation term containing the anisotropy of the first-order optical polarizability α(−ω;ω) is shown to yield the dominant contribution to the Kerr susceptibility χ(3)(−ω;ω,0,0). A class of special chromophores having negligible second-order polarizabilities β(−ω;ω,0) and large dipole moments μ has been identified in order to optimize this term. These chromophores are not subject to the efficiency-transparency tradeoff typically encountered with second-order nonlinear optical (NLO) chromophores, providing highly transparent materials with large PR Kerr response. Contrary to previous approaches in this field, the best-performing PR polymers are then expected to employ chromophores that would be useless for second- order applications (negligible β). We report PR of the material 30% 2,6-di-n-propyl-4H-pyran-4-ylidenemalononitrile (DPDCP): 15% N,N′-bis(3-methylphenyl)- N,N′-bis(phenyl)benzidine (TPD):55% poly(methyl methacrylate) (PMMA):0.3% C60 as an illustration of this principle. A 100 μm thick film of this material exhibits a steady-state diffraction efficiency of η=25% and net two-beam coupling of Γ=50 cm−1 at a bias field of 100 V/μm and a wavelength of 676 nm. The macroscopic Kerr susceptibility of the material is related to molecular electronic properties of the chromophore DPDCP which were independently determined by experiments in solution and by quantum chemical calculations.

A series of conjugated donor−acceptor trienes in which the central double bond is incorporated into an unsaturated isophorone, verbenone, or chromone ring has been synthesized. In each case, the donor group consists of an amine and an aromatic or heterocyclic ring system, and the acceptor is the dicyanomethylidene group. The nonlinear optical properties of each of the compounds has been measured and correlated with its structure. The dipole moments and molecular hyperpolarizabilities of these compounds, like those of other conjugated polyenes, are large enough to be used as the active components of electrooptic polymers. Unlike other donor−acceptor polyenes, however, these compounds exhibit the thermal stability required for such applications.