In this study we present a theoretical approach to simulate vibrational anharmonic coupling effects seen in the Raman spectra of oligo(para-phenylenes). Quantum chemical ab inito methods are applied to determine anharmonic force constants and energy corrections on the harmonic vibrational frequencies of the isolated molecules. Semiempirical methods are applied to compute Raman intensities of fundamentals and combination bands. This methodology is then used to characterize a previously unassigned Fermi resonance around 1600 cm-1. The evolution of this quantum mechanical resonance with oligomer length and planarity is compared to experimental data.

Ruthenium complexes with tridentate terpyridine type ligands have many structural advantages over the complexes with bipyridine ligands. Polynuclear ruthenium complexes prepared using these terpyridine ligands bridged with phenylene rings are potential candidates for photosensitization in dye-sensitized photovoltaic cells. In this study, we have carried out synthesis, characterization and theoretical modeling of rigid, rod-like homometallic dinuclear ruthenium complexes using terpyridine and bipyridine ligands. The photophysical and photovoltaic properties have been investigated. These supramolecular dyes are found to be efficient photosensitizers in dye-sensitized photovoltaic cells when a liquid electrolyte is employed.

Pentacene thin films were grown in ultra high vacuum on amorphous SiO2 and on a high dielectric constant material, crystalline BaTiO3. During pentacene deposition, substrates were held at three different temperatures (-650, 250 and 750 C). In general, three different morphologies were identified: a first closed interfacial layer, a thin film mode composed of faceted grains with single molecule step height, and a volume mode with features substantially higher than those of the thin film mode. Analysis was carried out by atomic force microscopy and in some cases by synchrotron X-ray diffraction.

Measurements of the third-order susceptibilities of new dithienylethylenes in solutions using a degenerate four wave mixing technique at λ=532 nm in picosecond regime were made. From these measurements we deduced the second order hyperpolarizabilities. Optical power limiting properties of the mentioned compounds using nanosecond laser pulses in the visible range are evaluated. The dispersion of nonlinear absorption coefficients is obtained. The appropriate quantum chemical calculations are carried out.

Self-organized oligosilane thin films possess molecular orientation normal to substrates with multilayered structure. This unique order of -conjugated molecules results in good hole transport properties. In the present work, carrier transport properties at low temperature are studied for 1,10-diethyldecamethylsilane polycrystalline films. Even at a temperature as low as 173 K, a time-of-flight transient photocurrent waveform showed a clear plateau and a sharp decay, whose shape is similar to that at room temperature. Their hole mobility followed Arrhenius type temperature dependence with a small activation energy of 0.09 eV. The hole mobility of 6.3×10-5cm2/Vs at 193 K was more than 2 orders of magnitude higher than that of typical polysilanes, which inevitably contain disordered structures hindering smooth carrier transport.

We describe detailed studies of ionically self-assembled monolayer (ISAM) photovoltaic (PV) devices incorporating various electron acceptor materials, such as fullerenes and phthalocyanines. Excitons are generated when the conducting polymer is irradiated, and the electron acceptors aid in dissociating the electron/hole pairs before they can radiatively recombine, thus improving the efficiency of the PV process. The ISAM technique allows the deposition of conducting polymer and electron acceptor materials in alternating layers of nanometer-scale thickness. This ensures that every photoexcited electron-hole pair is in proximity to an electron acceptor, thus minimizing electron-hole recombination and increasing the photocurrent. The individual thickness of each monolayer and the interpenetration of adjacent layers can be precisely controlled through the parameters of the electrolyte solutions. Using the ISAM technique, we have demonstrated that it is possible to create ultrathin films (100 nm) of PV material that have enhanced efficiencies.

Investigation into the temperature dependence of the surface morphology of a thin film of p-sexiphenyl (p-6P) on KCl(001) was carried out by atomic force microscopy (AFM). An individual p-6P film was prepared by vapor deposition at a base pressure of ∼1x10-8 mbar onto a KCl(001) surface which was maintained at 323 K during deposition. The AFM was carried out in a separate vacuum chamber, in situ, at a base pressure of ∼1x10-6 mbar. The p-6P film was cooled and maintained at discrete temperatures in the range from 294 K to 128 K as AFM measurements were performed. Similar surface morphologies are observed for film temperatures maintained at 294, 264, and 227 K, and 188 and 128 K during the AFM measurements. AFM images for the first set of film temperatures (294 - 227 K) indicate the presence of block-like islands of p-6P, with well-defined crystallite boundaries. AFM images of the films in the second set (188 and 128 K) indicate the presence of triangular wedge-shaped structures of p-6P preferentially aligned nearly in the direction of the [110]KCl. Comparison of these wedge-shaped structures at the indicated film temperatures reveals they are rotated by approximately 180° with respect to each other. Subsequent images of the surface of the p-6P film captured again at 294 K, after the final 128 K temperature study was completed, revealed the same surface features found for the initial 294 K film temperature.

We report combined scanning near-field optical microscopy (SNOM) and near-field photocurrent (NPC) imaging of a binary conjugated polymer blend. We find phase separation on a scale of about 5 μm, with a good correspondence between topographic, fluorescence, and photocurrent images. We excited at 488 nm, a wavelength at which only one of the two polymers absorbs light. Under this illumination regions that are high in the topography image show high luminescence and photocurrent.

The photoluminescence (PL) efficiencies in the different regions of the sample were determined by calculating the absorbed energy using the Bethe-Bouwkamp model, and knowledge about the chemical composition of the different phases of the polymer blend. The calculation also allowed us to conclude that the photocurrent generation efficiency (current/absorbed photons) of the different polymer phases is comparable within the limit of confidence of this experiment (±10 %).

The rapidly expanding field of organic semiconductors for display and low-cost electronic applications requires materials, which not only have high mobility but also benefit from solution processability and environmental stability. In this paper we present a new class of solution coatable organic materials with excellent stability to air and light. Spin-coated FET devices operate at ambient conditions without encapsulation and show p-type field-effect mobilities of 2 x 10-3 cm2V-1s-1 and on/off ratios greater than 104. Thin films can be deposited from common organic solvents onto a variety of substrates. These films are mechanically robust and can withstand temperatures in excess of 100 °C without significant changes in electrical performance. FET switching and transient characteristics at higher frequencies are also discussed. These types of materials should find applications in many areas of flexible electronics.

The synthesis of dual-mode optical molecular switching systems has been recently achieved. These systems were based on chiral helical-shaped alkenes in which the chirality can be reversibly modulated by light. In this work we report a theoretical study on the geometric and spectroscopic properties of these structures using the well-known semi-empirical methods PM3 (Parametric Method 3) and ZINDO/S-CI (Zerner's Intermediate Neglect of Differential Overlap -Spectroscopic - Configuration Interaction). Our results show that there are two stable conformers very close in energy for each possible molecular helicity presenting a barrier of ∼40 kcal/mol for bond rotation along the main molecular axis. Under protonation these barriers increase significantly and might explain why the protonation leads to the blocking of the switching process. We propose a scheme for the switching mechanism based on charge transfer and conformational changes during the isomer interconversion.

Indium-tin-oxide (ITO) is the most widely used material as a transparent electrode due to its excellent transparency and high conductivity. The devices based on bare ITO, however, exhibited inefficient hole injection due to insufficient high work function and required high drive voltages. Thus, various surface treatments of ITO have been attempted to change the work function of ITO in order to reduce the hole injection barrier height. Electroluminescent (EL) characteristics of devices were improved dramatically using ITO chemically modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By the use of reactive -COCl groups, ITO surfaces were modified quickly and the work function of the modified ITO was changed widely depending upon the permanent dipole moments introduced in p-position of benzoyl chloride. We also compared the performance of the EL devices with ITO modified with different binding groups (-SO2Cl, -COCl, and -PO2Cl2) of p-chlorobenzene derivatives. Finally, we examined the correlation between the change in the work function and the performance of the EL devices by the chemical modification and found that the enormous increase in ITO work function up to 0.9 eV is possible using phenylphosphoryl dichloride with a CF3-terminal group in p-position.

In order to improve power efficiency of organic electroluminescent (EL) devices, i.e., ITO/TPD/Alq3/Al, enhanced electron and hole injection at Alq3/Al and ITO/TPD interface, respectively, was attempted by designing proper charge injection at both interfaces. Enhanced charge recombination at TPD/Alq3 was also demonstrated. Here, ITO, TPD, Alq3, and Al are abbreviations for indium-tin-oxide, N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-1,1'-biphenyl-4,4'-diamine, tris(8-hydroxyquinoline) aluminum, and metal aluminum, respectively. Enhanced electron injection by introducing a thin layer of Li salts of fluoride, acetate, and benzoate was described. We have found that the electron injection was improved in the order of Li+, Na+, K+, Rb+, and Cs+, and Cs salts exhibited the best EL performance. Chemical modification of ITO has been attempted to fine-tuning the work function of ITO in order to reduce hole injection barrier height. EL characteristics were improved dramatically using ITO modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By using reactive -COCl groups, ITO surfaces were covered quickly and the work function of ITO was changed widely depending upon permanent dipole moments introduced in para-position of benzoyl chlorides. Correlation between the change in the work function of ITO and the EL characteristics was examined. The improvement of charge recombination was attained by increasing the interfacial areas, i.e. introducing a mixed layer of TPD and Alq3, or inserting a thin film of rubrene with a higher recombination efficiency.

Surface roughness of ITO (Indium Tin Oxide) was measured by AFM (Atomic Force Microscope) and the existence of spikes was verified. Then OLED (Organic Light Emitting Diode) devices made from those substrates were fabricated and their electrical properties were measured with an I-V measurement system. There is considerable difference in the reverse leakage current of OLEDs depending on the surface roughness of the substrate. We observed a good correlation of reverse leakage current with Rpv (Peak-to-Valley roughness), but the correlations between reverse leakage current and Ra (Average roughness) and Rrms (Root-Mean-Square roughness) are not as good.

The luminescence and related phenomena of a trinuclear silver organometallic complex has been studied from a theoretical viewpoint (B3LYP/6-31G* level). The study takes into account the relation between this compound and the [Au(CH3N=COCH3)3] that has been characterised and studied on the base of its solvoluminescence behaviour.

A styrene copolymer of 4-vinylbenzyl thiocyanate (PST-co-VBT) was employed as recording material for optical interference patterns with periods ∧ < 1 μm. Using lower intensity laser irradiation (4 mJ cm-2, λ = 266 nm), refractive index gratings were produced in PST-co-VBT by an UV induced photoisomerization SCN - NCS. Subsequent modification of the patterns with gaseous amines yielded surface relief gratings via the formation of derivatives of thiourea. Laser irradiation with higher pulse energies (7 mJ cm-2, λ = 266 nm) directly produced surface relief gratings (modulation depth 30 nm). These gratings were also reactive towards amine reagents and allowed a selective functionalization of the grooves of the relief (“reactive gratings”). Optically inscribed gratings in PST-co-VBT were employed as optical resonators for distributed feedback (DFB) lasing. With a laser dye (DCM) dissolved in PST-co-VBT, optically pumped DFB laser action was observed after inscribing index and relief gratings. The pumping threshold for lasing I th was 250 nJ cm-2 at λ = 532 nm.

As demonstrated for the example of a diamond and zinc blende structure of dielectric spheres, small inclusions of a low absorbing metal with the volume fraction fm can have a dramatic effect on a complete photonic band gap (CPBG) between the 2nd-3rd bands. For example, in the case of silica coated silver spheres, the CPBG opens for fm ≍ 1.1% and exceeds 5% for fm ≍ 2.5%. Consequently, any dielectric material can be used to fabricate a photonic crystal with a sizeable and robust CPBG in three dimensions. Absorption in the CPBG of 5% remains very small (≥ 2.6% for λ ≥ 750 nm). The structure enjoys almost perfect scaling, enabling one to scale the CPBG from microwaves down to ultraviolet wavelengths.

The stability of properties of luminescent polystyrene compositions depending on their material structure has been studied. The samples obtained by the methods of bulk polymerization and injection molding were used for the experiment. The influence of molecular mass distribution, supramolecular structure, plasticizer concentration and geometrical size of samples on the stability of their properties in severe conditions of natural and radiation aging has been investigated.

Photovoltaic effects in Schottky Junction cells composed with Au/head-tail poly(3-hexylthiophene) (HT-P3HT)/Al have been studied as a function of excitation photon energy and temperature. It has been found that photocarriers are effectively generated at the interface of HT-P3HT/Al from the excitation spectra of photocurrents (photoaction spectra), which were obtained upon illumination to the Au or Al sides. The photoaction spectra also suggest that the photocarrier generation occurs at around 2.3 eV and 3.5 eV, which correspond to the peak of φ-φ* absorption and the photon energy with lower optical density region, respectively. The mechanisms of photocarrier generation are discussed taking the role of the Schottky junction into consideration.

A carbazole N-substituted by an oxyethylene group was polymerized using oxidative electro-polymerization. Due to the hydrophilic properties of the oligooxyethylene substituent, this monomer can be electropolymerized in aqueous solution. An acidic medium is particularly appropriate in order to decrease the oxidation potential of the monomer and to obtain films mainly composed of oligomers as revealed by SEC analysis. More particularly interesting is the stability of such material during polarization. In acidic medium 1.25 mol.L-1 HClO4, 95% of the charge density was maintained after polarization for 7000 cycles which shows the good electrochemical stability of this material compared to other polycarbazoles. Moreover, films are electroactive in aqueous electrolytes and would be well-compatible with polyethylene-oxide solid electrolytes.

In order to increase the mechanical properties of the film, we have also electropolymerized an oligomer with pendant carbazole groups obtained by acid catalyzed cationic ring opening polymerization of [N(2,3-epoxypropyl)carbazole] which leads to a new dicarbazyl cross-linked polymer with cations solvating oxyethylene segments. Due to their tridimensional structure, the mechanical strength of these films is superior to that of a linear polycarbazole film. However, their electroactivity in aqueous electrolyte is poor. So, the electropolymerization of a mixture of both monomers ensures good mechanical properties and compatibility with hydrophilic electrolyte in view to prepare an electrochromic device.

We investigated molecular thin films fabricated using novel organic materials, such as dendrimers with a rhodamine B (Rh-B) core, by a pump-probe measurement for ultrafast time-resolved spectroscopy with a time resolution of approximately 160 fs. The photon energy transfer caused by the interaction of the dendrimer molecules was measured in terms of absorbance. The wavelength of the pump light was 550 nm and a white continuum light spanning from 450 nm to 750 nm was used as a probe light. A spin-coated molecular film made of dendrimer molecules with Rh-B core has a relatively high molecular density. We measured a strong stimulated emission at a wavelength of 612 nm, whose fast decay was assumed to be caused by intermolecular interactions between the dendrimer molecules with Rh-B core. The lifetime of the molecules in the excited state was measured to be as short as 10 ps. Several types of molecular films with different molecular densities were compared, and cases with different pump energies were also discussed.