Daniel R. Greve

Direct Visualization of the Nanoscale Morphology of Conducting Polythiophene Monolayers Studied by Electrostatic Force Microscopy

Understanding and control of the relation between the electronic transport properties and the morphology of conducting polymers is crucial for the further development and use of these materials because poor electronic properties of domain boundaries often limit the overall properties of the material. This is especially valid for field effect transistors, [1‐3] light emitting diodes, [4] and superconductivity in polymer compounds, [5‐7] where improved transport properties are essential for the further optimization of the organic materials as the electronically active layer in devices. The present paper provides the first direct images of the electronic domain structure in a conducting polymer thin film. The relation between structural and electronic properties of conducting polymers has previously been studied by various methods, including X-ray diffraction experiments [8‐12] and investigations of the temperature dependence of the conductivity [13‐16] as well as the electronic mobility. [17] The data have been evaluated by various models as for example Sheng’s fluctuation induced tunneling, [18,19] or a 1D resistor network model. [20] Although no specific model has been agreed upon, it is generally believed that transport in doped conducting polymers can be understood on the basis of a “metallic island” model, which is a composite model consisting of highly conducting crystalline regions surrounded by insulating amorphous regions. [21,22] However, a central unresolved issue is the

Directed self-assembly of amphiphilic regioregular polythiophenes on the nanometer scale

Regioregular polythiophenes possessing alternating hydrophobic and hydrophilic substituents have been synthesized and fully characterized. The amphiphilic nature of the polymer allows it to assemble at the air-water interface forming highly ordered domains. Directed self-assembly of the resulting conducting monolayer into a microelectronic chip structure is described.

Molecules with multi-directional charge-transfer (MDCT) transitions as promising chromophores for third order nonlinear optics

Based on quantum chemical calculations molecules with multi-directional charge-transfer (MDCT) transitions are shown to posses values of the 2. molecular hyperpolarizability, γ, significantly larger than their uni-directional charge-transfer (UDCT) analogues. Very interestingly the calculated linear optical properties shows no redshifts of the CT transitions on going from a UDCT molecule to the MDCT analogues having the same length of the donor-acceptor moiety. This finding is important in the context of optimized figure of merits/transparency trade-off.

Saturation effects in the nonlinear optical response of regioregular, highly conjugated poly(3-alkyl-thiophene) thin films

Abstract Third harmonic generation measurements on highly conjugated regioregular poly(3-dodecylthiophene) thin films using a fundamental wavelength of 1907 nm give an absolute value of χ(3)(-3ω;ω,ω,ω) = 4×10−11 esu. This value is the nonlinear susceptibility of the most highly conjugated polythiophene film reported to date (λmax= 555 nm). Comparison to less conjugated samples reveals a saturation in the dependence of χ(3) the effective conjugation length.

Large Nonlinear Optical Response of Acceptor Substituted bis(N-phenyldithiocarbimato)Nickel(II) Complexes and the Relation to Intramolecular Charge Transfer Transitions

Abstract The second molecular hyperpolarizability, γ, for bis(N-(4-nitrophenyl)dithiocarbimato)Ni(II) complexes incorporating two p-nitroaniline moieties in a centrosymmetric fashion is found from third harmonic generation measurements to be two orders of magnitude higher than the simple sum of the p-nitroaniline contributions. The molecules with γ values as high as 2×10 −33 esu were designed to have efficient “periphery-to-centre” charge transfer transitions demonstrated to be of paramount importance for the nonlinear response by comparison with similar complexes without efficient intramolecular charge transfer transitions.