Regioregular polythiophenes baring 3-(p-methoxyethoxyethoxy)-phenyl substituents (PEOPT) show high photoluminescence efficiencies. Exposing thin films of this polymer to vapors of chloroform or annealing them by heat treatment results in a red shift of the absorption maximum due to solvent or heat induced ordering which gives rise to more planar conformations. The fact, that annealed thin films of PEOPT exhibit absorption edges at relatively low energies and thus have an enhanced spectral range makes them suitable for use in photodiodes / solar cells. The photoinduced charge generation efficiency in PEOPT is significantly enhanced by the addition of a strong electron acceptor like fullerene, as observed by quenching of the luminescence and by photoinduced absorption measurements in the infrared and UV-Vis regime. The efficiency of the photoinduced charge transfer from PEOPT to a methanofullerene is found to depend on the ordering of PEOPT in thin films.

The mass transporting properties of the surface relief grating (SRG) photofabrication on azobenzene polymer films is discussed precisely using an existing fluid mechanics model. Formulation for the SRG inscription rate is derived analytically from Navier-Stokes equation. In consequence, the dependence of inscription rate of the SRG on the experimental and geometrical parameters was explained very well by the model. The photoinduced surface deformation with an onedimensional Gaussian laser beam was also carried out in order to establish the validity and the generality of our fluid mechanics model. The experimentally obtained surface deformation profile is well reproduced by the theoretical model generalized for arbitrary force field profile.

In this contribution we compare experimental investigations (of photoluminescence, absorption and modulation spectroscopy) for a number of novel dye molecules to quantum-chemical simulations. The investigated materials contain phenylene-, phenylenevinylene-, naphthylene- and anthrylene units linked either by saturated or non saturated bonds. In the first part of the paper we give a short overview of the principal optical properties of the investigated molecules including a discussion of exciton localization effects. The latter can be accomplished by studying the geometry modifications in the excited state relative to the ground state. To do so, we couple the Austin Model 1 (AM1) approach to a multi-electron configuration interaction technique (MECI). The optical spectra are subsequently obtained from the Intermediate Neglect of Differential Overlap (INDO) Hamiltonian combined with a Single Configuration Interaction (SCI) approach. In the main section of this contribution we show the results of singlet exciton lifetime measurements performed with a modulation technique. An excellent agreement was found between the experimental data and quantum-chemical simulations for the transition dipole moments

With the advent of efficient and relatively inexpensive pulsed and CW laser systems for both civilian and military applications, the need for adequate eye and sensor protection is becoming increasingly important. While it is possible to filter out harmful wavelengths if the laser frequency is known, the proliferation of frequency agile laser sources underscores the need for “smart” passive materials that can sense the incident wavelength and provide protection. There has been considerable progress made in recent years in the design of optical power limiting (OPL) materials that can function by a variety of mechanisms, most of which derive their limiting behavior from some type of nonlinear absorption process. The most well-studied of these processes involve excited state absorption in which the absorption cross-sections of the photo-generated transient species are much greater than the original S0 to S1 transition. In this presentation we will discuss the efficacy of charge transfer species for optical limiting, and the need for more and better electron acceptor species.

The optical properties of substituted and unsubstituted oligothiophenes are analysed with respect to their supramolecular organization in the solid state. The spectra typical of the isolated molecules are obtained by reducing the intermolecular interactions by both lateral chain substitution and by inclusion in a host organic crystal. The photophysical properties of the weakly interacting oligothiophenes are strongly influenced by their backbone conformation and conformational mobility. Oligomers included in the channels of a guest crystal show fast torsional relaxation processes during the photoexcitation. Powders of β-substituted oligomers display optical properties dependent on the conformation of their particular chain packing arrangement.

Solution spectra of perylenetetracarboxylic dianhydride (PTCDA) show an equilibrium between monomers and dimers, with fluorescence exclusively from monomers and absorption from both. The dimer absorption follows closely the spectrum of PTCDA stacks in crystalline films, which indicate strong coupling to a molecular vibration and mixing of Frenkel and charge-transfer excitons. The same model accounts for solution spectra.

Correlated quantum-chemical calculations performed on supermolecular structures, i.e., on clusters made of several oligomer chains in interaction, provide insight into structure-property relationships in well-organized molecular films. This supermolecular approach is applied to crystalline phases of two prototypical conjugated oligomers and shows that variations in chain packing can lead to dramatically different optical (Davydov) splittings and carrier mobilities. Optimal chain organizations for various types of devices are discussed.

Difference infrared spectra between illumination and dark of a polyethylenedioxythiophene (PEDOT) covered germanium electrode in contact with the electrolyte solution and under applied potential are shown. The spectra show a different behavior at different redox (doping) states of the polymer. The photoinduced formation of positive charge carriers was found by illumination of the neutral (undoped) form, wheras no significant spectral changes occur in the oxidized (p-doped) and reduced (n-doped) form of PEDOT.

The recent development in nonlinear optical polymer materials and device fabrication technologies has resulted in a significantly reduced halfwave voltage for high-speed optical communications. In this paper, optical push-pull and active cladding approaches are discussed for low halfwave voltage electrooptic polymer modulator design and fabrication. Based on these new designs, experimental polymer modulators were fabricated and a halfwave voltage-interaction length product of 2.2 V-cm was achieved using optical push-pull and a highly active electrooptic polymer system.

Polymer light-emitting devices with a conducting polymer distributed Bragg reflector (DBR) are reported. Polymer DBRs were formed from alternate spin-coating of poly (3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulphonate) (PSS) as the low-index layer and a hole-transporting polyfluorene derivative as the high-index layer onto ITO deposited glass substrates. The polymer DBR with 5 periods showed reflectivity of 40% at the wavelength of 560nm. Onto this polymer DBR, a green-light-emitting polyfluorene was spin-coated to give the emissive layer and Ca/Al was deposited to form the cathode served another reflector. These LEDs operated successfully at low voltages and emitted light having a narrower spectrum (FWHM=47nm) than structures without the DBR (FWHM=102nm). The peak wavelengths varied corresponding to the thickness of the emissive layer, that is, the cavity length as expected from calculations. The luminance turn-on voltage of the LED with the polymer DBR is 2V, which is the same as LEDs without a DBR. The current was found to be limited by injection in the low field region and limited by space charge density at high fields. The current does not depend on the number of layers in the DBR in the low field region, and this implies that there are no effective energy barriers in the polymer DBR.

A series of tetrahedral tetramers of 2,5-diphenyl substituted 1,3,4-oxadiazole compounds were synthesized and characterized for electron-transporting layer (ETL) in organic light-emitting diode (OLED). The multiple-branch design of the oxadiazole tetramers intends to increase the melting temperature and to generate glass phase of the low molar mass derivative such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). We observed temperatures of the glass phase transition for the oxadiazole tetramer with appropriate peripheral substituents, indicative of amorphous characteristics of the molecule in spite of highly symmetrical molecular framework. The luminescence-current-voltage characteristics of multilayer OLED devices containing the oxadiazole tetramer or PBD as ETL were examined to evaluate the efficiency of our multiple-branch molecular design.

A series of novel ionic chromophores consisting of a carbazole moiety and pyridinium rings connected by a double bond have been designed and synthesized as nonlinear optical materials. Their linear and nonlinear optical properties were investigated by semiempirical calculation and experiment. The absorption maximum wavelengths (lmax) of these ionic chromophores showed shifting to longer wavelength region than their corresponding electrically neutral compounds. These ionic chromophores possess large first hyperpolarizabilities (b).

Phthalonitrile and its derivatives react with Tin(II) reagents to give intensely colored linear oligomers. Structures are proposed for the oligomers based on elemental analysis, infrared, 1H and 13C spectra, and mass spectra. Stannous chloride has two kinds of properties, reducing reagent and Lewis acid. Tin(II) alkoxide initiates phthalonitrile oligomeriaztion when excess alkoxide is present. The mass spectrum indicates a chain length of at least a hexamer. In semi-empirical AM1 calculations, the helical conformation of a pentamer is indicated to be more stable than a linear conformation. The position of the electronic spectral maximum can be controlled by different kinds of reaction conditions and solution absorption and emission spectra were recorded.

A mass controlled layer-by-layer sequenitial adsorption process for polyelectlrolytes was newly developed for the fabrication of functional devices using ultra-thin organic film formed by various polymers of different polarity of charge. In this study hydrophobic Ruthenium complex monomer • tris(bipyridyl) ruthenium(II) hexafluorophosphate • was micelle-wrapped with an anionic surfactant, sodium dodecylbenzenesulfonate, and was assembled with PAH (poly (allylamine hydrochloride)), which has the opposite charge, on ITO substrates. With this method, we succeeded in fabricating ultra-thin organic films even when the adsorption material is not polymer but monomer. Moreover it was found that the film thickness of the self-assembled Ru micelle/PAH had a linear relationship with the number of bilayers. By using this process, an EL device was fabricated by depositing the thin film of micelle-wrapping ruthenium complex monomer on ITO and metal electrode on top of the film. Light emission was observed by applying voltage to this device.

The organic materials presented here, e.g. cyano-ether-PPV, different bisarylamidine-perylenes and conventional as well as substituted forms of phthalocyanines exhibit the advantages of low processing costs and the simplicity of tuning their optical properties. Hence they are promising candidates to be used in large area photovoltaic applications. The investigated cells consist of one or two organic layers sandwiched between electrodes of indium tin oxide (ITO) and aluminum. The experimental techniques of electroabsorption(EA)- spectroscopy, photocurrent-action spectroscopy and current voltage characterization were used to gain further insight into the process of charge generation, charge separation and transport of the charged species to the electrodes. To enhance the quantum efficiencies of the photovoltaic cells, combinations of organic materials with electron-accepting and electron- donating properties in multilayer devices were investigated. We chose the organic materials copper-phthalocyanine and a bisarylamidineperylene whose HOMO and LUMO level alignment should favor a charge transfer process in order to increase the photocurrent(PC) responsivity by enhanced exciton dissociation. Additionally, one of the two layers of a double layer device was blended with small amounts of the material constituting the second layer to further increase charge carrier generation by extending the dissociation zone.

Ionically self-assembled monolayer (ISAM) films are a recently developed class of materials that allows detailed structural and thickness control at the sub-nanometer level combined with ease of manufacturing and low cost. The ISAM fabrication method simply involves the dipping of a charged substrate alternately into polycationic and polyanionic aqueous solutions at room temperatures. Importantly, the ISAM technique yields exceptionally homogeneous, large area films with excellent control of total film thickness. We describe detailed studies of ISAM light emitting diodes incorporating poly(para-phenylene vinylene) (PPV) as the light emitting polymer. The individual thickness of each monolayer and the interpenetration of adjacent layers can be precisely controlled through the parameters of the electrolyte solutions. The effects of the pH and ionic strength of the immersion solutions, the total film thickness, and the PPV thermal conversion parameters on the photoluminescence and electroluminescence yields have been systematically studied. The ISAM process also allows the advantage of depositing well-defined thicknesses of separate polymers at the indium tin oxide and the aluminum electrode interfaces.

Study of the electronic spectra of conjugated oligomers can provide a useful approach to obtain an analysis of the often complicated spectra of their corresponding polymers. One advantage of studying oligomers is that there is often a well defined conformational morphology and one may eliminate or reduce the spectral consequences of a distribution of conjugation lengths. In the present work, electronic spectra of some oligomers of poly-5,5'-(4,4'-dinonyl-2,2'bithiazole) were studied, both in solution and in the solid state, and the results compared with spectra of the polymer. For solution data, the plot of molar extinction coefficient vs. the number of double bonds is found to be linear, as is the Kuhn plot. This is consistent with quantum-chemical molecular modeling calculations, and closely resembles the behavior of other conjugated oligomers, such as polythiophenes and polyenes. However, the solid state spectra exhibit a large red shift in both absorption and emission. These and other results suggest the presence of strong intermolecular interactions in the solid state that significantly modify the magnitude of the homo-lumo gap of the oligothiazoles and their polymers. By comparing oligothiazoles in solution to thin film results, polymer behavior is explored.

Ionically self-assembled monolayers have been recently shown to spontaneously produce the noncentrosymmetric ordering that is required for a second order nonlinear optical (NLO) response. The precise thickness of each monolayer is determined by variables such as the pH and ionic strength of the immersion solutions. We show here that the relationship between polymer conformation and layer thickness dramatically affects the magnitude of the NLO response. The largest χ(2) values are found in the thinnest films, indicating that the NLO response is determined primarily by chromophores located at the layer interfaces, as opposed to those within the bulk of a layer.

We have determined the crystal structures of regioregular HH-TT oligomers with a variety of side chains, including hydroxy-bearing side chains capable of H-bonding. The H-bonding orders the molecular packing into infinite 2-D sheets of Φ-stacks. In these H-bonded sheets, the Φ-stacks are insulated from each other by the aliphatic side chains and form one-dimensional “wires”. In contrast, the structures of similar oligomers that do not have H-bonded side-chains feature a structure in which neighboring Φ-stacks in are in contact (“shorted wires”). The effects of these differing molecular arrangements on the spectral properties and exciton splitting are discussed.

The solid state luminescent properties of new statistical copolymers of 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene and a porphyrin-substituted phenylene vinylene are reported. The photoluminescence, PL, emission shows an efficient energy transfer to the porphyrin, in spite of the small absorption coefficient of the porphyrin in the wavelength range of the poly [2-methoxy-5-(2'- ethylhexyloxy)-1,4-phenylene vinylene], MEH-PPV, emission. At a porphyrin content of 0.25%, by weight, the emission is already dominated by the porphyrin. The PL efficiency of these copolymers is significantly reduced from the value of 13% for MEH-PPV down to 3% for the copolymer with 10.84% of porphyrin. Efficient energy transfer is also observed in the emission spectra of light-emitting diodes.