Cyclobutenedione (CD) as a new electron acceptor for second order nonlinear optical materials is reported. After syntheses and evaluation of new materials containing CD, it is observed that CD is not only a strong electron acceptor to enhance second order molecular hyperpolarizability (β), but also the first substituent to control the molecular orientation in crystals. Compared with nitro (NO2) subsutitent, CD is shown to be advantageous in higher molecular absorption coefficient (ε), shorter λcut-off and easy introduction of chirality with hydrogen bonds into organic molecules. These advantages are useful to produce higher β values and second order nonlinear optical coefficients (dIJK) than nitro analogue, by controlling the molecular orientation in bulk crystals. In particular, CD substituted with chiral 1-amino-2-propanol is shown by x-ray crystallographic analyses to have a function to control molecular orientation one dimensionally in a mono-molecular plate of crystals with space group P1. By oriented gas model, very large d-values including off-diagonals were obtained. From the analysis of the Maker fringe pattern, the coefficient d11 of DAD ((-)-1-(4-dimethyl aminophenyl)-2-(2-hydroxypropylamino)cyclobutene-3,4-dione) was measured to be 200±40 pm/V.

The application of ele ctroactive organic materials in devices (light emitting diodes, photovoltaic cells) often requires electrodes with a low workfunction. Commonly, aluminum or alkaline earth metals are used, which usually exhibit strong interaction with the organic material, such as the formation of new covalent bonds or doping. This results in a strong modification of the electronic structure of the organic/metal interface, and in most cases does not yield the energy level alignment expected for the unreacted interface. As a n alternative to the above-mentioned metals we propose the use of samarium, with a workfunction of 2.7 eV, for the following reason: we have studied the interface formation between Sm and p -sexiphenyl (6P, which exhibits intense blue electroluminescence), with ultraviolet photoelectron spectroscopy. Sm was deposited stepwise onto thin films of 6P in ultrahigh vacuum, and the photoelectron spectra were recorded after each step. We did not find any indication for a strong interaction between the two materials. Metallic Sm is formed instantaneously and the valence electronic structure of 6P remains unchanged upon the metal deposition. The weak interaction at this interface allows one to determine the energy level alignment between a metal and an organic material in a direct manner from the photoelectron spectra, without the need for making any assumptions on the workfunction or ionization potential.

Bis(diglycidyl)ether of bisphenol-A-aniline (BP-AN) based second-order nonlinear optical (NLO) polymers containing triene chromophores have been developed through post-polymer functionalization reactions. One-pot aldol condensation reaction of dicyanomethylidene functionalized verbenone as well as isophorone compounds with aldehyde functionalized BP-AN polymer enabled the introduction of various chromophore moieties with high degree of functionalization. These polymers were studied using various structural (1H NMR, FTIR), linear (UV-Vis) and NLO characterization techniques. A d33 value of ca. 139 pm/V at 1.064 µm was determined for a representative polymer containing verbenone unit. We have observed fast photo-bleaching in these polymers. Detailed studies on the photophysical properties of this class of materials have been carried out using various analytical techniques, the structure-properties relationship and photo-bleaching mechanisms will be presented.

Molecular beam deposition of quaterthiophene oligomer on a single crystal of potassium acid phtalate yields thin films exhibiting a novel supramolecular organisation which has been determined by a combined study of X-ray diffraction and polarized optical transmission measurements. In this structure consisting of stacks of tilted H aggregates, a commensurate ratio between the KAP substrate and the overgrown oligothiophene layer (quasi-epitaxial growth) is attained. The samples are optically extremely anisotropic, with the projection of the molecular axis on the substrate surface perfectly aligned along the b crystallographic axis. Using these novel structural data, the optical properties are interpreted within the framework of the transition density approach.

Vapor deposited double-layer (DL) organic light emitting diodes (OLEDs) based on the combination of materials belonging to the triaryldiamine family as hole transporting materials (HTM) and metal complexes of 8-hydroxyquinoline as electron transporting materials (ETM) have been characterized. As HTM N,N'-bis(diphenyl-4-yl)-N,N'-diphenyl-benzidine (NBDB), N,N'-(naphthalen-1-yl)-N,N'-diphenyl-benzidine (NPB) or N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine (TPD) were used. As ETM tris-(8-hydroxyquinolinate)-Al(III) (Alq3) or bis-(8-hydroxyquinolinate)-Zn(II) (Znq2) were used. The typical cell configuration was: ITO/HTM/ETM/Ca,Ag. A comparison of the electrical and light emitting features between devices constructed with the new molecule NBDB and NPB or TPD was made, with the aim of improving their efficiency and stability.

In this report, we describe the photo-induced in-plane alignment of nematic liquid crystal (LC) molecules, 5CB, in a hybrid cell with alternate self-assembled films of low-molecular weight azobenzene dye and polyelectrolyte on gold electrodes using the attenuated total reflection (ATR) measurement method. The molecular self-assembly process was also investigated by the ATR method. Reflectivities due to excitations of the surface plasmon polariton (SPP) were observed in the ATR properties of the LC cell. In-plane switching of the LC molecules adjacent to the aligning layer was evaluated from the ATR curves after irradiation of linearly polarized visible light to the LC cell. The sensitivity of the ATR method gives information on the alignment, tilt angle, and extent of LC reorientation in the bulk. Thus, the importance of using the molecular self-assembly processes of individual polyion-dye pairs for fabrication of new photo-aligning layers is emphasized.

We report here on our continued investigations of the synthesis and characterization of new metal-containing polymers incorporating 8-hydroxyquinoline. We reported earlier on three types of linear metal-containing polymers with ether, ester and amide functionalities in the chain's backbone. In this report, we extended our previous studies by targeting star-shaped metal-containing polymers. Again, these polymers still have the favorable structural characteristics, which would allow for a large degree of control over their physio-chemical properties.

Metal deposition on a p-sexiphenyl (6P) film was studied by ultraviolet photoelectron spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and X-ray photoelectron spectroscopy (XPS). The deposited metals were Au, Mg, and several alkali metals (K, Na, Rb, and Cs). No chemical reaction between 6P and Au or Mg was observed in the measured spectra, while additional gap states appeared in the UPS and MAES spectra by deposition of the alkali metals. The diffusion of Au and Mg atoms into the 6P film was observed in the MAES spectra. We found the trend of the vacuum level shift is different between the systems of the 6P on the Au and its reversed systems (Au on the 6P film), suggesting the different formation of the interface depending on the deposition sequence.

Oligo (p-phenylene vinylene)s OPV were synthesized having cyanobiphenyloxy-groups bonded to the vinylene double bonds via alkylene spacers. A Pd(0)-reaction was used to synthesize the oligomers starting with the dibromo-substituted benzene and the alkenyloxy-biphenyl-nitrile. The orientation of the mesogens by a magnetic field and their influence on the orientation of the main chain was investigated by means of neutron diffraction ND. Data on the photophysics of the oligomers were gained using several spectroscopic methods such as UV/VIS, polarized optical microscopy POM, SEC, 1H-NMR, FT-IR.

Monolayer films of poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV) supported on highly orientated pyrolytic graphite (HOPG) have been investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). While there are areas of the surface covered with a featureless polymer layer, we also observe large regions with surprisingly long range order. Structural models of the polymer, as well as tunneling spectra, suggest that this ordering is derived from substrate-polymer epitaxy.

We have studied the photophysical properties and energy transfer processes in tris(phenylquinoxalines ) (TPQ). TPQs emit blue fluorescence with a maximum at 2.9 eV as well as green phosphorescence at 2.2 eV. When doped with a phosphorescent dye efficient energy transfer takes place from the excited singlet and triplet state of the TPQ host to the guest molecules. The mechanism of energy transfer can be understood in the frame of Förster's theory of dipole-dipole interaction. Besides the interesting photophysical properties, TPQs are also very efficient electron transport materials. Red light-emitting diodes utilizing doped TPQ as emitter and electron transport layer have been prepared and electroluminescence properties investigated.

The structural, electrical and electrochemical properties of nanoparticle thin films derived by a one-step exchange-crosslinking-precipitation route were characterized by microscopic, spectroscopic and electrochemical techniques. Thiolate-encapsulated gold nanocrystals of 2-nm and 5-nm core sizes and alkyldithiol crosslinkers were studied as a model system. The mixing of the two components in solutions allowed sequential exchanging, crosslinking and precipitation of dithiol-crosslinked nanocrystal thin films. The films were specularly reflecting and electronically continuous, and have potential applications in catalysis and molecular recognition.

We determined the internal electric field distribution in light emitting electro-chemical cells (LECs) and light emitting diodes (LEDs) based on methyl substituted poly(paraphenylen) (mLPPP) by performing electroabsorption measurements as a function of an external bias voltage. Based on these results we outline the working principle of both types of devices. In the case of the LEC we observed an abrupt increase in the EA signal above a threshold voltage of about 2V which we attributed to junction formation due to in-situ electrochemical doping. For single layer LEDs we found the behavior expected for metal/insulator/metal/structures, i.e. the electric field drops linearly over the bulk polymer and no space-charge regions were observed.

These findings are important for improving the performance of organic electroluminescent devices.

Conjugated polyelectrolytes, poly[2-(3-thienyl)-ethanolhydroxycarbonylmethylurethane] (HPURET) and PDA from 5,7-dodecadiyn-1,12-bis-(hydroxycarbonylmethylurethane) (HP4BCMU), were processed by programmed electrostatic assembly, respectively, with two different polycations that have significantly different refractive indices – one is poly(diallydimethylammonium) chloride (PDADMAC), the other poly(4-vinyl pyridine) quaternized with dimethylsulfate (QPVP). The optical properties of these conjugated polymers have been studied with particular attention to local environmental effects and adaption (post-assembly-processing). The electronic absorption spectra of these assemblies were dependent on the details of the assembly process.

Two series of highly hyperpolarizable nonlinear optical (NLO) chromophores, containing perfluoroaryl dicyanovinyl and phenyl tetracyanobutadienyl acceptors, have been designed and synthesized. These chromophores show good thermal and chemical stability. The 3D conformational structures, confirmed by computational modeling, enhance polymer matrix compatibility and decrease optical loss of the polymer films. The guest-host polymers of the chromophores show large electro-optical activities.

The indium tin oxide (ITO) anodes for organic light emitting diode (OLED) were made from an oxidised target with In2O3 and SnO2 in a weight proportion of 9:1 using the RF magnetron sputtering method. The comparable ITO anodes with different carrier concentrations were prepared by varying the hydrogen partial pressure during film deposition. The current-luminance-voltage characteristics of the devices indicated that a high carrier concentration in ITO plays a role in improving OLED performance. A maximum efficiency of 3.8 cd/A was achieved when an ITO anode with a higher carrier concentration of 9×1020 cm−3 was used in a fluorene based OLED. This efficiency is about 1.5 times higher than that of an identical device made with an ITO anode having a lower carrier concentration of 5×1020 cm−3. The increase in electroluminescent efficie ncy reflects an enhanced hole-injection in the device. We consider that enhanced hole injection is due to the reduced band bending in ITO when it has a high carrier concentration

Organic light emitting device (OLED) with a microcavity structure has been fabricated. A kind of chirped distributed Bragg reflector (DBR) and a metal Al film was used as the two reflectors of the microcavity. A multimode light emission was achieved due to the structure of the microcavity. The emission peaks of the microcavity were located at 476nm, 520nm, 597nm and 626nm, respectively.

Diazoluminomelanin (DALM) is a luminescent polymer belonging to the broader class of conjugated polyphenylene materials, which has shown significant optical activity in response to perturbing fields. In this paper we use semiempirical electronic structure calculations and molecular dynamics simulations to investigate the molecular structure and absorption characteristics of model phenolic oligomers. Molecular dynamics simulations show the polymer backbone can be extremely flexible depending upon the ionization state of the phenolic hydroxyl groups. The interring torsion angle is a critical variable as it relates charge localization effects and electronic excitation energies. Comparison with experimental data demonstrates the need for a multistate basis to describe the absorption properties of this system.

The charge transport in high quality single crystals of various organic molecular semiconductors is investigated. Band-like motion in delocalized states is observed in various polyacene and oligothiophene single crystals. The electric field dependence of the mobility is ascribed to acoustic phonon scattering. Furthermore, hot carrier effects can be observed at low temperatures and high electric fields. Band-like transport changes over to hopping motion when the effective bandwidth shrinks, i.e. at high temperatures or in crystallographic directions of small molecular orbital overlap.

New rigid rods amphiphilic molecules based on phenyl ethynylenes oligomers with hydrophilic side chains were synthesized by step by step method. The two most interesting products, the pentamer and the heptamer are enough amphiphilic to give stable Langmuir films that are able to be deposited as LB film on substrates as hydro-philic glass, ITO or hydrophilic silicon. A good transfer ratio of 1 is observed only by lifting, which suggests a Z type deposited film. A multilayer deposition can be carried out to 36 layers. The well structured films of 3.7 nm thick which are observed by X ray reflectivity suggest a rearragement in Y–type bilayer. By AFM, the observed irregular surface with steps of 3.7 and 1.8 nm high or multiples is coherent with a self-rearrangement of the single deposited layer to a double layer during the drying phase. The heptamer and pentamer show large stokes-shifts with a high photoluminescence emission peak at 516 and 504 nm respectively. LED properties were demonstrated using the ITO/oligoPY/ LiF-Al sandwich yielding photon emission at 516 nm for the heptamer. The electroluminescent device yields in the range of 10−3%. The demonstration of electroluminescence in a LB film of molecules aligned parallel to the substrate is very interesting because it confirms the possibility to tailor conduction and emission properties of the devices using a layer by layer deposition technique.