The layered MIIPS3 compounds posess a unique cation exchange intercalation chemistry, which allows the synthesis of a wide range of air stable M1-xPS3G2x intercalates (G stands here for a Monocation). The positive charge of the guest cations is counterbalanced by intralayer metallic vacancies.

Intercalation exerts a dramatic influence on the magnetic properties of these compounds. Whereas pristine MPS3 compounds order antiferromagnetically (M = Mn, Fe‥), Many intercalates become magnets below an ordering temperature that can be as high as 92 K. The role of intercalation is discussed in terms of the creation of intralayer metallic vacancies, which destroy the spin balance that prevails in pristine MPS3 compounds.

The MPS3 host lattice has the capability of causing spontaneous poling of the dimethylamino-N-Methyl stilbazolium chromophore (DAMS), leading to materials that exhibit strong second harmonic generation. (SHG). Inserting DAMS into MnPS3 therefore leads to a composite that possess both spontaneous Magnetization (below Tc = 40 K) and a strong efficiency for SHG.

New naphthalene-sulfur compounds, oligomers of poly (l,4-naphthylene sulfide), have been synthesized and studied by electronic and vibrational spectroscopy in both pristine and oxidized forms. It has been found that the charged defects induced on these molecules are Much More stable than in the corresponding 1,4-phenylene derivatives. Nevertheless their physical properties are strongly affected by steric effects which hinder a regular arrangement of the repeating units.

The temperature and field dependence of the de Haas-van Alphen oscillations in θ- (BEDT-TTF)2l3 is analyzed. The cyclotron masses are estimated to be 2.0 Me and 3.6 me for slow and fast oscillations, respectively. The indication of magnetic breakdown effect is discussed in terms of the geometry of the Fermi surface. The results are compared with those of the infrared reflectance spectra.

The Shubnikov-de Haas (SdH) and Magnetoresistance Measurements have been performed in an organic Metal β″ (BEDT-TTF)2AuBr2. Absence of saturation in the magnetoresistance up to 13T suggests that this salt is a compensated Metal. The SdH oscillations are consistently understood by assuming that three cylindrical Fermi surfaces are present. The frequencies of the SdH oscillations corresponding to the Fermi surfaces are determined to be 41.5 T, 139 T, and 181 T for H//b*-axis. An anomalous maximum in the resistance is found at about 9.5 K for H//b*-axis although no anomaly is observed for H//plane.

Luminescence with maximum near 1.96 eV of organic donor compound bis (ethylenedi-thio) tetrathiafulvalene (BEDT-TTF) was observed in crystals and frozen at low temperature solution. It was found that solid state effects sharply reveal themselves in excitation spectra of the substance and have almost no influence on the shape of the emission. Intensity of the emission is strong at liquid He temperature but rapidly decreases with heating of the sample as well as after modification of charged state of molecules forming the crystal and is very weak in case of Monovalent (BEDT-TTF) Br salt. Shape of the luminescence spectra correlates with the absorption of the investigated compounds. The data obtained can be interpreted assuming dimer-like arrangement of molecules in the crystal structure.

Conjugated polymers can be use to provide charge transport and emissive layers in a range of thin-film electroluminescent devices. Electroluminescence results from radiative decay of excitons which are formed by electron-hole capture. Device efficiency is particularly sensitive to the balancing of electron and hole currents injected from opposite electrodes, and this is best achieved at the heterojunction between two polymer layers with different electronegativities. We report here the properties of a conjugated polymer with high electron affinity, a cyano derivative of poly (p-phenylene vinylene), PPV. This polymer shows an electron affinity considerably higher than than that of PPV, and is therefore suitable for use as the electron transporting layer in heterostructure LEDs. It shows efficient photoluminescence due to radiative decay of singlet excitons, and photoinduced absorption in the IR, similar to that in PPV, which we attribute to excitations of photogenerated triplet excitons. EL devices formed with a heterojunction between PPV and this cyano derivative of PPV, with indium/tin oxide as positive electrode, PPV, cyano-PPV layers and an aluminium negative electrode, show internal quantum efficiencies as high as 4%.

The title oligomers have been incorporated in Zr-based layers on quartz substrates. Absorbance and emission spectra and fluorescence decays have been measured on these films and compared with data from solutions, powders, and PPV. The samples may be divided into those with “liquid-like” behavior and “solid-like” behavior; the latter is characterized by blue-shifted absorbance, red-shifted emission, and more complex decay dynamics than the former. By these criteria, the layers and PPV itself are decidedly “solid-like’.

Polymeric light emitting devices may be fabricated from a simple structure consisting of a low work function cathode (typically calcium or Magnesium), a conjugated semiconducting polymer and a transparent anode (typically indium-tin oxide). Optimum device efficiencies require the balanced injection of electrons and holes. This paper describes the application of molecular engineering in the design of a family of poly (cyanoterephthalylidenene) s which show increased electron affinity over the unsubstituted analogue [poly (p-phenylenevinylene) PPV]. In particular these polymers as the emissive layer in a bilayer device with indium tin oxide (ITO, positive transparent contact) and aluminum (stable negative contact) and PPV as a hole transporting layer exhibit internal efficiencies up to 4%.

We describe bilayer structures comprised of a poly (p-phenylene vinylene) (PPV) layer and a trap-free diaryldiamine (TPD) doped in polycarbonate (PC) layer, sandwiched between indium-tin-oxide (ITO) and aluminum (Al) contacts. Two critical phenomena in the operation of polymer based electroluminescent devices, interface injection and carrier range, are investigated. It is established that the ITO/PPV contact is capable of sustaining dark current under trap-free space-charge-limited (TFSCL) conditions into a hole transporting TPD:PC layer. TFSCL currents are not observed in devices without the PPV layer. Upon increasing the thickness of the PPV layer a deviation from the TFSCL regime is observed which is attributed to trapping of the injected holes within PPV. These observations suggest a novel method for estimating the trapping Mobility-lifetime product μτ for holes in PPV. By this means we estimate μτ ∼ 10−9 cm2/V.

Conjugated polymers have been intensively studied in connection with high conductivity on doping, large nonlinear optical responses in their semiconducting state, and recently[1] as novel light-emitting diodes (LEDs). Many different polymers are realized in Fig. 1 on varying the substituents R, including the best characterized examples[2,3] that have centrosymmetric conjugated backbones in their idealized extended geometry. The PS and PPV families fluoresce strongly, the PT family Moderately, and the PDA's or PA hardly at all. We have related [4,5] polymer fluorescence to the nature of the lowest singlet excited state, Si, which in C2h symmetry is either a dipole-allowed Bu or a two-photon allowed Ag state. Since the ground state is Ag, S1 is either 1B or 2A and fluorescence requires E (1B) < E(2A). The idea is simply that radiationless decay wins out for the low excitation energies and many vibrational degrees of freedom of conjugated polymers unless Si has a strong transition dipole to the ground state.

The light-emitting diodes (LEDs) using semiconducting oligothiophenes, dimethylquater-thiophene (DMQtT, tetramer), dimethylquinquethiophene (DMQqT, pentamer) and dimethyl-sexithiophene (DMSxT, hexamer), have been investigated. These oligomers were deposited on ITO-coated glass in ultra high vacuum and an aluminum electrode was subsequently vacuum-deposited on top of the oligomers. These structures have the diode configuration with Schottky barrier between the oligomers and aluminum.

The LED using DMSxT shows good rectifying feature with the rectifying ratio of 1500 at ±10V.Red-orange emission is clearly observed above 4V bias. In this LED, DMSxT acts not only as an emitting layer but also as a hole transport layer. We have also fabricated and studied alternate layered structures of DMSxT/DMQtT and DMSxT/DMQqT as the emitting layer. In these configurations, the carrier recombination can be modulated because both DMQtT and DMQqT have energy gaps wider than that of DMSxT.The quantum efficiencies (photons emitted per carriers injected) of the LEDs using DMSxT/DMQtT and DMSxT/DMQqT are about one hundred times and one thousand times larger than that of the LED solely based on DMSxT, respectively. These results indicate that the layered structures are advantageous in increasing quantum efficiency of the emission.

The potential of organic materials for nonlinear optics was recognized early with the identification of charge transfer concepts for second order Materials, and π-electron delocalization in conjugated polymers for third order effects.[l,2] Nevertheless, they have not been seriously considered for applications until the past five years over which applications to electro-optics have been vigorously pursued. At this point many of the relevant technological problems for electro-optics have been faced and solved. This progress has been driven by imminent applications in information processing and communications. Frequency conversion, specifically doubling of near infrared lasers into the blue for data storage etc., also relies on the second order nonlinearities. But progress towards efficient doublers has been dominated by other well-established Materials such as KTP and LiNbO3 because of the short time window perceived for applications.[3,4] However, because of the inherently large nonlinearities associated with organic Materials, one would expect that ultimately the most efficient doubling devices could be made from organic Materials.

In this paper, we report our recent developments in achieving thermally stable polyimides that possess large second order nonlinear optical activity. We have developed several classes of novel chromophores based on the combination of efficient thiophene conjugating units and novel electron-donating and electron-accepting functional groups. Through these developments, we have synthesized chromophores that possess non-resonant βμ values as high as 9,100 × 10−48 esu measured at 1.9 μm. These chromophores also possess improved thermal and chemical stabilities. The incorporation of these chromophores in high temperature polyimides produces E-O Materials with high linear electro-optic coefficients (in excess of 15 pm/V at 1.3 μm) and long-term temporal stability at an elevated temperature of 150°C for more than 800 hours.

Organic nonlinear optical (NLO) polymers must possess large and stable bulk nonlinear properties if they are to be of practical use. Numerous classes of NLO chromophores and polymers have already been evaluated but the selection process, particularly as related to stability issues, has been very stochastic in nature. If suitable chromophores are to be successfully identified their thermochemical degradation Mechanisms Must be elucidated and structural modifications introduced in a rational fashion. We have devised a protocol for the evaluation of NLO chromophores which involves initial screening by thermal analysis (DSC and TGA) and selected molecular hyperpolarizability (EFISH) analysis. The Most promising candidates are incorporated into thermoplastic polymer hosts where bulk nonlinear properties (dijand rij) and additional thermal stability properties are evaluated by spectroscopie Means (UV-VIS). Cyclicvoltammetry (CV) has been identified as a useful tool for evaluation of these chromophores; in the case of azobenzenes with aliphatic amine donor and a nitro acceptor a correlation between the thermal stability and oxidation potential has been found. The Most facile thermal degradation mechanism which occurs in these dyes has been identified and structural changes to the donor group have been introduced to avert the process.

Second harmonic generation from the spin coated films of an asymmetrically substituted polydiacetylene, namely poly ((8-butoxy carbonyl) Methyl urethanyl) l- (5-pyrimidyl) -octa-l,3-diyne (BPOD) is reported for the first time. The Macromolecules assemble to produce the organization responsible for SHG without recourse to poling. d33 of the spin coated film (0.19–0.31 μm thickness) are between 0.78–0.88 pm/V without absorption correction and 3.32–5.57 pm/V after correction. Angular and polarization dependence study of the second harmonic response suggests that the film has in-plane isotropy as a whole and the net dipole is nearly perpendicular to the film surface. Spontaneous orientation of the polymer chains during the film formation seems to be responsible for the noncentrosymmetric alignment of the polymer. SHG from the Langmuir Blodgett films are also reported.

A new experimental approach has been developed which allows characterization of rotational dynamics of NLO chromophores in amorphous polymers over 12 decades in time, from 10-6 to 106 sec. Measurements over such a broad distribution in relaxation times are important not only in determining how the chromophore orientational dynamics are coupled to polymer dynamics but also in making accurate predictions of the temporal stability of technological interest. In particular, accurate characterization over a broad range of time scales reveals that NLO polymers meet technological requirements more easily than is predicted using a less complete characterization.

Molecular design of processable nonlinear optical (NLO) polymers is discussed for applications to devices such as ultrafast optical switches. Channel waveguides must be fabricated in order to develop polymeric NLO switching devices that can be driven with lower laser power. For these purposes, we propose molecular structures that reduce attenuation loss and allow the development of highly processable NLO polymers. Third-order nonlinear optical properties, χ(3), of the novel NLO polymers are around 10−10 esu in the 1.5 μm wavelength region. Even in off-resonant regions, the χ(3) values are around 5 × 10−11 esu. Single Mode channel waveguides of the polymers are fabricated using a standard photo-process. Attenuation loss through a film and also for a single mode waveguide at 1.32 μm wavelength is Measured. Nonlinear optical properties of novel, processable, heteroaromatic polymers with large χ(3) are also discussed. Several types of heteroaromatic polymers are developed with a structure in which π-electron excessive heteroaromatic compounds and π-electron deficient heteroaromatic compounds are combined to induce strong nonlinearity. The charge transfer between heteroaromatic rings on the π-conjugated sequences is thought to influence the properties of certain excited states that enhance χ(3) These polymers have excellent potential for use in fabrication of optical switching devices.

We have developed a novel class of double-end crosslinkable (DEC) chromophores. Processible side-chain nonlinear optical (NLO) polymers with crosslinkable groups at the ends of chromophore pendants were synthesized from DEC Monomers. The polymers were processed into good quality films, which were subsequently poled with a corona setup and thermally cured to attain stable noncentrosymmetric order. Using this DEC approach, we have realized large optical nonlinearities (χ(2) = 90–220 pm/V) with long term stability at 125 °C.

Preparation and characterization of novel dye-doped polyimide films for electrooptics is described. Thermal stabilities of donor-acceptor 2,5-diaryl oxazoles were evaluated by differential scanning calorimetry. Absorptive losses in thin films of Ultradel 9000D® doped with donor-acceptor oxazoles were measured by photothermal deflection spectroscopy. Absorptive losses at high doping levels may be explainable by dye-dye aggregation or dye degradation during the curing process. Lower doping levels, however, show losses of ≤ 3.0 dB/cm at 830 nm and ≤ 2.4 dB/cm at 1320 nm.

Disperse Red-1 type chromophores were attached to the backbones of PMMA, polyvinyl-phenol as well as the styrene-Maleimide alternative copolymer and glass transition temperatures of these three polymer derivatives were in the range of 125, 165, and 245°C, respectively. We have also, for the first time, attached EO chromophores to some thermostable cardo-polymers. Fluorene derivatives in which the 2- and 7-positions were substituted with an electron accepting and an electron donating substitutem, respectively, were made polymerizable through their reactive functional groups at the 9,9′-positions. Various condensation polymers were prepared. These polymers are amorphous, film-forming, thermostable, and having Tg ranging from 150 to 300°C. These polymers exhibit strong electro-optic properties after electrode poling. Thermal stabilities of these polymers were compared by following the spectral decay of the chromophore and the decay of the electro-optic coefficient. The loss of EO activity at elevated temperature can be realized as a combination of chromophore reorientation and chemical degradation.