We report the apparent hysteresis cycles in the protonation/deprotonation induced conductor-insulator transition for a water-soluble double-strand polyaniline. Experimental evidences show that the polymeric complexes of polyaniline and poly(styrene sulfonic acid) are soluble in water as non-aggregated single molecules. Although the hysteresis loop becomes narrower within 40 hours and the bistability is not permanent, the rate of collapse of the hysteresis loop is extremely slow for a solvated polymer in water. The water soluble polyaniline was compared with solid state samples of PAN:HCl. It was found that, under thermodynamically identical conditions, the memory effect is stronger for the water-soluble polyaniline than the water-insoluble solid of PAN:HCI.

Langmuir-Blodgett (LB) bilayers of organophosphonic acids can be prepared where the phosphonic acid headgroups bind metal ions to form the same layered extended-solid structures present in solid-state metal phosphonates. The inorganic extended-solid network enhances the stability of the LB films, but can also be designed to introduce physical properties, such as magnetism, that are typical of the inorganic solid-state. By preparing films based on functionalized organophosphonic acids, the metal phosphonate approach can be used to produce “dualnetwork” LB films, where both the organic and inorganic networks add function to the thin film assembly. To begin to understand the design constraints associated with dual-network metal phosphonate films, LB bilayers of a phosphonic acidderivatized azobenzene amphiphile are formed with Cd2+ and La3+ and the structures are compared to octadecylphosphonate LB films prepared with the same metals.

ac Susceptometry has been used to study a number of magnetic molecular solids including a new compound, Mn(II) octaethyltetraazaporphyrin, α-MnOETAP, and decamethylmanganocenium tetracyanoethenide, Mn(Cp*)2•TCNE, a previously reported molecule-based ferromagnet. Both of these compounds exhibit signatures of ferromagnetism including significant hysteresis below 2 K and rapidly increasing χT (where χ is the molar susceptibility) with decreasing temperature. However, their ac susceptibility data show relatively strong dependence of χ′ and χ″ on the frequency of the applied field, indicating a spinglass state. Other molecular ferromagnetic solids examined show much less sensitivity. These studies indicate that the standard practice of characterization by dc and ac susceptometry at a single frequency are clearly insufficient for identifying the magnetic state of a molecular solid.

Recent progress in the study on magnetic properties of molecular soft ferromagnet TDAE-C60 (where TDAE is tetrakis(dimethylamino) ethylene) is reported. Both crystalline and thin film samples are prepared by the diffusion method and the temperature and field dependence of magnetization are studied by SQUID magnetometer. The magnetic behaviors of single crystals were found to vary from sample to sample. In best single crystals, the saturation magnetization as high as 1.0 μB/C60 has been observed. Spontaneous magnetization and its temperature dependence was evaluated from the Arrott plot. The ferromagnetic phase transition was also observed in TDAE-C60 thin films.

We report our investigations into tetrathiafulvalene (TTF) derivatives bearing N-methylthiocarbamoyl and halogen substituents which engage in intermolecular interactions in the solid state. The synthesis of new donors is presented, along with the X-ray crystal structures of some of these derivatives and their radical ion salts.

The electronic structure of the two organic, layered metals κ-ET2Cu(SCN)2 and K-ET 2Cu[N(CN)2]Br has been studied using a combination of soft X-ray emission (SXE) and soft X-ray absorption (SXA) spectroscopy. These techniques are powerful probes of the site and angular-momentum resolved partial density of states (PDOS) for both occupied and unoccupied states. Therefore these spectroscopies are particularly suited for an analysis of the density of states of multi-atomic, complex materials as the ET-based organic conductors, allowing site-specific electronic structure to be measured. Furthermore, for certain materials, the electronic structure of specific layers can be measured. We present a preliminary picture of the electronic structure of κ-ET 2Cu(SCN)2 and κ-ET 2Cu[N(CN)2]Br as measured by SXE and SXA performed at the C-Is and N- Is core levels.

Solid charge transfer (CT) complexes of C60 with TSeC1-TTF, EDT-TTF, EOET-TTF, and TDAP (1, 3, 6, 8-tetrakis(dimethylamino)pyrene) were newly prepared. All the obtained black crystals were proved to be neutral despite of their rather strong electron donor ability. Lattice parameters of them except for EOET-TTF complex were determined together with those of HMTTeF·C60, which had been reported with different values. Rubidium doping under a mild condition was examined on the complexes of TDAP, EOET-TTF, HMTTeF, BEDT-TTF, hydroquinone and ferrocene to search for the superconductors of new crystal and electronic structures. Among them, the rubidium-doped ferrocene complex easily showed an apparent superconducting signal in SQUID magnetization measurements. The doping effect on these CT complexes is compared to that on OMTTF complex.

We report the synthesis and characterization of a soluble metal complex polymer for electroluminescent (EL) applications. The polymer was prepared by the reaction of a zinc Schiff base with 4,4′-diphenylmethane-diisocyanate. The polymer is amorphous and with glass transition temperature of 156 °C and is soluble in common organic solvents such as chloroform, tetrahydrofuran (THF), and N-methylpyrrolidinone (NMP). High optical quality films were obtained by spin-coating the polymer solution of THF. The zinc Schiff base, and the polyurethane (PU) shows strong photoluminescence under a UV-lamp illumination. Single and double layer EL devices consisting ITO/hole transfer layer (HTL)/PU/Al have been fabricated and characterized. The results indicated that the complex polymer could act as both electron transport and emissive layers for EL devices.

Blue light emitting devices (LED) with para-hexaphenyl (PHP) as the active material and aluminum as cathode exhibit very high quantum efficiencies. To further optimize device performance it is crucial to understand the physical properties of the involved interfaces. We have performed Rutherford-Backscattering experiments on actual devices to show the importance of oxygen in the interface formation at the cathode as this leads to the formation of a layer of AlxOy between PHP and aluminum. In devices, where the organic film is exposed to air before the metal electrode is evaporated, an insulating layer on the metal-side therefore is inherent. It has been shown that the introduction of an intermediate layer between active material and electrodes results in a higher quantum efficiency of the LED, the most common concepts being charge-transport-layers, or insulators on the other hand. Our results underline the need for a better control of the LED processing. Ultraviolet- and X-ray photoelectron spectroscopy in situ growth studies of thin aluminum films on PHP have been made to reveal the change in the electronic structure of the active medium in a LED in the absence of oxygen. Also the direct interaction of oxygen with this organic material is investigated by photoelectron spectroscopy.

We investigated the structural and electronic properties of samples of polyparaphenylene (PPP), derived from two synthesis methods (the Kovacic and Yamamoto methods). These samples have been subjected to different heat-treatment temperatures (650 °C ≤ THT ≤ 2000°C) and their properties are compared to the polymer prior to heat-treatment (THT=0°C). The photoluminescence (PL) spectra of heat-treated PPP based on the two synthesis methods reflects the differences in electronic structure of the starting polymers. The PL emission from the heat-treated Yamamoto polymer is quenched at much lower THT than from the Kovacic material. However, Raman spectra taken of the material resulting from heat-treatment of the polymer (using both preparation methods) indicate the presence of phonon modes for PPP in samples at THT up to 650°C.

Aluminum tris(8-hydroxyquinoline) (Alq3) is presently considered one of the most reliable electron transporting and emitting materials for molecular-based organic light emitting diodes (OLEDs). This paper discusses the effects of sample morphology on the hydrolysis and photoluminescence response of Alq3. The evolution of 8-hydroxyquinoline (8-Hq), a volatile byproduct of the hydrolysis of Alq3, was quantified using gas chromatography/mass spectroscopy (GC/MS) analysis on samples of different morphology. Annealed (more crystalline) samples exhibited greater chemical stability than freshly sublimed films, at the expense of photoluminescence efficiency. These phenomena are discussed with respect to possible failure mechanisms that Alq3-based OLEDs might undergo during prolonged operation.

Multilayer films were fabricated employing a new layer-by-layer complexation technique by alternatively dipping substrates in solutions of macromolecular ligands and Eu3+ ions. A luminescent poly[2-(3-thienyl)ethanol hydroxycarbonyl-methyl urethane] (H-PURET) was prepared by hydrolysis of thiophene polymer, poly[2-(3-thienyl)ethanol butoxycarbonyl-methyl urethane] (PURET), which was developed in our laboratory. H-PURET was used as macromolecular ligands. The multilayer deposition was monitored using UV-visible spectroscopy. As the number of bilayers increases, the absorption due to the polymer increases. The multilayer films were characterized by infrared and fluorescence spectroscopic techniques. Electroluminescence brightness easily obtained from the multilayer film of conjugated polymer-Eu3+ complex was measured to be about 40nW.

A new segmented polymer (3) consisting of a distyrylbenzene chromophore separated by polyethylene glycol segments has been prepared by two independent methods: a novel, polymer analogous Mitsunobu reaction and conventional double displacement reaction. The polymer is soluble in a variety of organic solvents, forms excellent, optically clear films and exhibits strong fluorescence. The properties of the chromophore and the polymer, as well as the scope and limitations of the novel Mitsonobu polymerization are presented. Attempts to use polymer (3) in electroluminescent devices are also discussed.

Reversible electroluminescence color changes with applied voltage have been observed in light-emitting diodes fabricated from semiconducting polymer heterojunctions consisting of an electron transporting polybenzobisthiazole and hole transporting poly(p-phenylene vinylene) when layer thicknesses are less than 60–100 nm. Enhanced device performances such as lower turn-on voltage and higher efficiency and luminance were also obtained compared to single-layer devices. The observed voltage-switchable emission colors in these nanoscale heterojunction light sources can be understood in terms of spatial confinement effects which are related to field-dependent charge transport and trapping processes in the materials. These results also demonstrate the use of new high temperature rigid-rod polymers as electron transport and emissive layers in electroluminescent devices.

Electroluminescence from a series of polymers and copolymers which exhibit photoinduced excited-state intramolecular proton transfer (ESIPT) is reported. Among these polymers containing ESIPT moieties in the main chain or side chain are poly(1,4-(2-hydroxy)phenylene benzobisthiazole-co-decamethylene benzobisthiazole), poly(styrene-co-3-hydroxy-4′-ethenylflavone) and poly(2,5-benzoxazolediyl(2,2,2,-trifluoro-1-(trifluoromethyl) ethylidene)-5,2-benzoxazolediyl-4-hydroxy-1,3-phenylene). The electroluminescence spectra of these polymers are identical to their photoluminescence spectra, indicating that electroluminecence originates from electrically-generated intramolecular proton transfer (EGIPT). Because electroluminescence from EGIPT implies electrically-induced population inversion, these results demonstrate the possibility of electrically-pumped organic solid-state laser diodes.

Two series of new electroactive and photoactive coil-rod-coil and rod-coil-rod triblock copolymers, poly (pentadecamethylene carboxester)-block - poly(p-phenylene benzobisthiazole) - block - poly (pentadecamethylene carboxester) (1), and poly(2,6-benzoxazole)-block poly(benzobisthiazole decamethylene)-block-poly(2,6-benzoxazole) (2), were synthesized, characterized, and used to investigate the self-assembly properties of rod-coil block copolymers. The progressive band narrowing of the absorption spectrum of thin films of 1 confirmed the effects of spatial confinement with increasing coil block size. Photoluminescence studies of thin films of 1 and 2 showed the effects of self-organization, annealing at 110 °C, block lengths, and composition on photophysical properties. Bilayer photoreceptors consisting of a layer of block copolymer as the charge generation layer and a layer of tris(p-tolyl)amine dispersed in polycarbonate as a trap-free hole transport layer were oberved to have high quantum efficiency, good photosensitivity and good dark decay.

A new thiophene-based compound 2,5 bis[2'-(4”-hydroxyhexanol benzyl)-l'-ethyl]3,4-dibutyl thiophene (HBDT) as well as a copolymer (HBDT-PU) consisting of alternating HBDT and urethane spacer units were synthesized. Absorption and luminescence properties of both compounds were studied in solution and in different polymer matrices. Absorption and luminescence spectra of HBDT and HBDT-PU coincide indicating that emission in HBDT-PU occurs from the thiopene containing unit. Photoluminescence (PL) is emitted in the blue-green region of the visible spectrum with a maximum at 460 nm. The PL efficiency of both compounds is strongly enhanced when dispersed in a PVK or PMMA matrix indicating that concentration quenching occurs in the pure material. Light emitting devices were fabricated utilizing a PVK/PBD blend doped with HBDT and HBDT-PU at different concentrations as emitter material. The electroluminescence (EL) spectra coincided with the PL spectra of HBDT indicating that EL emission originates from the dopant molecules. The dependence of the EL efficiency on the doping concentration was measured and found to be close to the concentration dependence of the PL quantum yield.

Single crystal X-ray structures of salt complexes of oligoquinoline, 2,2'-bis(4- phenylquinoline)-1,4-phenylene (4), with p-toluenesulfonic acid, trifluoromethanesulfonic acid and a laser dye, Sulforhodamine 101 hydrate have been determined and used to study the effects of molecular packing on physical and photophysical properties of conjugated oligomer and polymers. UV-vis and emission spectra of thin films of the oligoquinoline-p-toluenesulfonate complex were also performed. These results indicate that they form an intermolecular charge-transfer complex. These complexes serve as models of quarternized polyquinolines such as the self-assembled bilayer films of polyquinoline and polystyrenesulfonic acid.

Multicolor electroluminescent (EL) device which emits red (R), green (G) and blue (B) light has been realized by stacking a two-color emission part and a single-color emission part. The former part consists of two emissive layers of red and blue light, which can be selected by changing the polarity of applied field. The latter part consists of a single emissive layer of green light. The emission color from the R-G-B emission device can be modulated by the combination of applying various voltages to the two-color and to the single-color emission parts, separately.

Control of organic interfaces by insertion of a thin inorganic film (SiO) has been investigated for an organic electroluminescent (EL) diode which consists of 8-hydroxyquinoline aluminum (Alq3) and diamine derivative (TPD). In order to evaluate optical quality of the emissive layer at the interface, thin film of emissive marker layer was inserted into the emissive layer at the interface between the emissive layer and the carrier transport layer. The EL emission spectrum and the optical characteristics have been discussed for the EL diode with and without inorganic film.