All organic photoreceptors are now widely deployed in electrophotographic copiers and printers and represent the most important and commercially successful application of electronic organic materials. The need to optimize polymers for this application has stimulated fundamental investigations of charge generation, injection and transport processes in the disordered organic solid state. Electronic transport in a wide variety of glassy polymeric insulators has been studied by the time of flight drift mobility technique. It is typically found to proceed by a field driven chain of thermally activated tunneling events among active, compositionally identical, but energetically inequivalent sites. The inequivalece of site energies is attributed to the combined effect of disorder and site relaxation. Polymeric systems which differ widely in composition and morphology are found to exhibit a remarkably recurrent pattern of features in their transport behavior. Theoretical attempts to account for these universal features have been frustrated by their inability to explain the sublinear field dependence of the drift mobility and its variation with temperature. The drift mobility of polymers can be systematically modified by doping. Doping studies have provided the design rules which enable the fabrication of trap free polymers. The latter are an absolute requirement in electrophotography.

Charge carrier (hole) mobility in amorphous organic polymeric materiats can be changed at will over at least nine orders of magnitude without increasing the conductivity of the polymers, and also without affecting the carrier range, i.e., without introducing deep traps. The changes in the drift mobility can be accomplished by several means: (1) by changing the density of hopping sites (the concentration of transport-active molecules or groups), (2) by light doping the host polymer with low-oxidation potential compounds (for hole transport), and, eventually, (3) by the nature of the host medium and its polarity. Since the carrier mobility is typically activated and electric field dependent, significant changes can also be made by varying the temperature and the electric field. An enhancement of mobility by heavy doping has also been described. Hole mobilities in the small molecule - host polymer composites and also in polymers in which the transport states are backbone-derived can thus be varied from values below the measurement threshold (<10−10 cm2 V− s−1) to fairly high values in the neighborhood of 10−1 cm2 V−1 s−1 at an electric field of E = 105 V cm−1 and at 295 K.

The relevance of photochemistry in the electrical fatigue of organic layered photoconductors is discussed. A hole transport molecule DEH undergoes a photocyclization reaction in the charge transport layer to an indazole derivative, causing residual surface charges to persist during light decay. A dye chlorodiane blue, in the presence of DEH, initiates photochemistry at the hole transport/carrier generation interface resulting in chemical consumption of the dye. An activation energy of 15 – 20 kcal/mol is reported for the dye bleaching reaction.

Charge-dipole interaction effects in molecularly doped polymers are discussed. The charge-dipole Coulomb interaction makes exponentially distributed traps. Calculating the mobility with their traps leads to mobility behavior like Gill's equation. The cancellation of a dipole corresponds to coincidence events of small-polaron hopping.

Using femtosecond pump-probe spectroscopy, bleaching of the π-π* absorption Q-band, and photo-induced absorption on the high energy side of the Q-band, have been observed and time-resolved in a nearly-amorphous thin film of fluoro-aluminum phthalocyanine. Following excitation, the induced absorption signal develops as the absorption saturation signal diminishes, suggesting exciton decay into a subgap state. The different bimolecular decay dynamics observed for the absorption saturation (τeff ≈700 fs) and induced absorption (τeff ≈ 2 ps) signals support this conclusion. Possible origins of the subgap state are discussed. In addition, polarization-dependent spectral hole burning is observed at very early times. These results suggest the need for exploration of thin phthalocyanine films which are ordered in three dimensions over distances of at least 200–300 Å. Initial femtosecond results for epitaxially-grown chloro-indium phthalocyanine structures, which meet these criteria, are similar to those for the nearly-amorphous film, but indicate an additional polarization-dependent photo-induced absorption within the Q-band.

A stable monolayer was formed by spreading a chloroform solution of a photosensitive ionic amphiphilic compound on an aqueous subphase containing an ionic polymer with opposite charge. In addition to the increase in stability, the cross sectional area of the amphiphilic molecule usually increased on polyion complexation from that of the same amphiphilic molecule in the absence of the ionic polymer. Deposition of the monolayer onto the solid substrate as a very homogeneous LB film was possible. The increase in molecular area allows various photochemical reactions, which otherwise do not occur due to the steric hindrance, to proceed in the resulting LB films. A rapid decrease in emission of the polyion complexed pyrene LB films was observed upon UV irradiation in air. Application of this very sensitive quenching procedure to optical memory will be also presented.

Amorphous high-Tg polymers films containing electron-donor-electronacceptor substituted azobenzene groups can be used as reversible optical storage materials. Optical information can be “written” on the film with a polarized argon laser beam and “read” with a low power HeNe laser. Erasing can be performed with a circularly polarized writing beam. A significant number of writing/erasing cycles can be performed on the same spot. Potential applications in optical memory, holographic storage, waveguides and second harmonic generation are discussed.

The fluorescent characteristics of lanthanide chelates are of considerable interest in connection with electronic energy transfer processes and with their use in laser systems. We have synthesized various chelating groups, such as diketone and bypyridyl containing polymers and prepared their Tb3+ and Eu3+ complexes. Their fluorescent properties in connection with a possible laser action were investigated.

Electroluminscence (EL) in organic compounds has been investigated from fundamental as well as practical point of views. Various organic dyes were utilized as emitter materials in EL devices. In these examples, owing to the broad nature of the luminescence spectra of organic dyes, the luminescent colors are dull. We have utilized lanthanide metal ion complexes as a luminescent emitter.

Tb and Eu ion complexes emitted sharp green and red light, respectively. The configuration of the EL cell and experimental results are described.

A series of synthetic enzyme mimics of the dimanganese catalase enzyme from bacterial cells has been prepared and the chemical mechanism of their activity has been examined. These are formulated as [LMn2X]Y2, μ2-X = CH3CO2−, ClCH2CO2−, Cl−, OH−; Y = ClO4−, BPh4−, CH3COO−, Cl−, Br−, utilizing the septadentate ligand, HL = N,N,N′,N′-tetrakis(benzimidazole)-1,3-diaminopropan-2-ol. These catalyze the disproportionation of H2O2 into O2 and H2O by a mechanism indistinguishable from the enzyme mechanism. Like the enzyme three electrons can be removed from Mn to form four oxidation states ranging from Mn2(II,II) to Mn2(III,IV). The electrochemical properties, the energy level spacing between electronic spin states (S =0, 1..5), ligand exchange and disproportionation kinetics can be controlled by the choice of the bridging ligand X. The mechanism involves the cyclic oxidation and reduction of the Mn2(II,II) and Mn3(III,III) species by H2O. An important component of the kinetic barrier in the rate-limiting step appears to be the free energy required for oxidation to the Mn2(III,III) species. This is determined by the Mn ligands. An ENDOR study of the manganese catalase(III,IV) from T. thermophilus has revealed the Mn coordination environment to be predominantly carboxylate protein residues. This ligand environment greatly lowers the barrier to oxidation, enabling catalysis at rates approaching the diffusion limit.

Monoclonal antibodies against meso-tetrakis(4-carboxyphenyl porphine)(TCPP) were prepared by immunizing Balb/c mice with TCPP bound keyhole limpet hemocyanin covalently and fusing the spleen cells with myeloma cells by using poly(ethylene glycol). The antibodies bind TCPP strongly with the dissociation constants of 10−6−2.5 × 10−7 M. One of the antibodies causes a large shift of the Soret band of TCPP to a longer wavelength and large induced Cotton effects(ICD) on TCPP. Quantitative analyses of the binding of TCPP to the antibody by ICD show that not only one-to-one binding but two-to one(binding site: TCPP) binding occurs in excess of the antibody over TCPP.

Synthetic ether-linked bolaform amphiphile vesicles and a novel gramicidin-porphyrin “diad” have been prepared. Photoinduced electron transfer properties of the diad were compared in bilayer (dihexadecylphosphate, DHP) and monolayer (2,2′-0-didecyl-1,1′-0-eicosamethylene-racdiglycero- 3,3′-diphosphoric acid, PS20) membrane vesicles with dithiothreitol sacrificial donor and methyl viologen electron acceptor present on both vesicle membrane surfaces. Although the rates of methyl viologen photoreduction varied depending on the mode of diad orientation within DHP bilayer membranes, photoreduction rates were not orientation-dependent in bolaform membrane vesicles containing the gramicidinporphyrin diad. The relevance of these results on vectorial electron transfer processes in closed membrane systems is briefly discussed.

Copper-zinc superoxide dismutase (CuZnSOD), myoglobin, hemoglobin and glucose oxidase are encapsulated in stable, optically transparent, porous, silica glass matrices synthesized under mild conditions using novel sol-gel synthetic techniques. The biomolecules retain their characteristic reactivities and spectroscopic properties. The porous glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within the pores. The chemical reactions of the immobilized proteins are monitored by means of changes in their visible absorption spectra. Four encapsulated proteins are studied: CuZnSOD reacts with CN−; metmyoglobin is reduced to its deoxy form and then reacts with O2 to make the oxy form and CO to make the carbonyl form; methemoglobin is reduced to its deoxy form and reacted with CO to make the carbonyl form; and glucose oxidase is reacted with glucose to make gluconic acid.

Various MOCVD (metal-organic chemical vapour deposition) type precursors and their self-assembled semiconductor nanocluster products [1] have been investigated in zeolite Y hosts. From analysis of in situ observations (FTIR, UV-vis reflectance, Mössbauer, MAS-NMR) of the reaction sequences and structural features of the precursors and products (EXAFS and Rietveld refinement of powder XRD data) the zeolite is viewed as providing a macrospheroidal, multidendate coordination environment towards encapsulated guests. By thinking about the α- and β-cages of the zeolite Y host effectively as a zeolate ligand composed of interconnected aluminosilicate “crown ether-like” building blocks, the materials chemist is able to better understand and exploit the reactivity and coordination properties of the zeolite internal surface for the anchoring and self-assembly of a wide range of encapsulated guests. This approach helps with the design of synthetic strategies for creating novel guest-host inclusion compounds having possible applications in areas of materials science such as nonlinear optics, quantum electronics, and size/shape selective catalysis.

23Na double rotation NMR (DOR) provides information on site-specific adsorption of guest molecules within the porous framework of sodium zeolite Y. Anchoring of molybdenum-hexacarbonyl to extraframework Na+ cations in particular locations within the large α-cavities is detected. Changes of the chemical environments of the Na+ cations are observed upon loading trimethylphosphine molecules. Spin-lattice relaxation measurements yield insight on dynamic aspects of the anchoring sodium cations.

This paper describes the photorefractive properties of a new and growing class of materials exhibiting the effect, doped nonlinear organic polymers. We show directly using a PMMA-based copolymer with a pendant nonlinear nitroaminotolane chromophore doped with a charge transport agent that the presence of photoconductivity and optical nonlinearity are only necessary, but not sufficient to guarantee that a given materials system will yield measurable photorefractive gratings, rather than gratings due to some other process such as photochromism. To prove photorefractivity unequivocally, direct measurement of the spatial phase shift between the intensity pattern and the index modulation is best, and we summarize a convenient way to do this using two-beam coupling and sample translation. In addition to the photorefractive epoxy materials such as bisA-NPDA:DEH reported earlier (Phys. Rev. Lett. 66, 1846 (1991); Proc. SPIE1560, 278 (1992)), a new PMMA-based copolymer with pendant p-nitroaniline chromophores doped with DEH also shows photorefractive grating formation, with writing speed 100 times higher than that for the epoxy material.

The photorefractive effect has been recently observed by holographic grating formation in optically non-linear polymers molecularly doped with charge transport agents. Grating formation can be understood as a four-step process, the first three of which dictate the photoconductive response: charge generation, mobility and trapping. The fourth step is modulation of the refractive index by the resulting space-charge field, via the electro-optic effect. We present the results of photoconductivity experiments to determine charge generation efficiency, carrier mobility and the kinetics of recombination and trapping, focussing primarily on the epoxy polymer bisphenol-A-diglycidylether 4-nitro-1, 2-phenylenediaminc (bisA-NPDA) doped with the hole transport agent, diethylaminobenzaldehyde-diphenylhydrazone (DEH). The electric field dependence of the generation efficiency and mobility differ in detail from results on other molecularly doped polymers.

We present experimental and theoretical results on electro-optical properties of some polymeric films. Specifically, we report on our measurements regarding a new, completely polymeric and potentially photorefractive material with a large electro-optic coefficient and photoconductivity. Furthermore, we summarize our investigations of electro-absorption in a DCH polydiacetylene where the important contributions of continuum threshold on the nonlinear and electro-optical properties of conjugated polymers are emphasized.

Photoconducting electrooptic polymers are a new class of photorefractive material. Most applications of photorefractive materials require the formation of a space-charge grating. The formation of space-charge gratings in photorefractive semiconductors has been studied extensively. We consider the formation of photorefractive gratings in a polymer.

Photoconductivity in photocrosslinkable second-order nonlinear optical (NLO) polymeric materials and photovoltage generation in a poled guest-host polymer are reported. These NLO polymers have been functionalized with crosslinkable cinnamoyl groups and show relatively stable second-order optical nonlinearities at room temperature when poled and crosslinked. Without introducing any photosensitizer or charge carrier transport agents, photoconductivity was obtained in these polymer systems. Optical excitations of the NLO chromophores lead to photocarrier generation and it is conjectured that these NLO chromophores also play a role in the carrier transport. In addition to photoconductivity, photovoltage generation was observed in the dye doped polymer upon poling. This poled polymer also exhibits a polarization dependent photovoltage when illuminated by light in the absorption region of the NLO chromophore.

This paper deals with the application of some recently developed evanescent waveoptical techniques for the characterization of novel macromolecular host-guest systems. In particular, surface plasmon- and guided optical wave-spectroscopies and -microscopies are used to determine the linear and nonlinear optical properties of these materials in thin film form.