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In this contribution we describe a combined experimental and theoretical study of the relation between the molecular structure and the electronic properties of conjugated donor-acceptor type chromophores for light-harvesting applications. A series of model systems was synthesized where a central anthracene (electron donor) is connected to dicyanovinyl units (electron acceptor) through a π-conjugated spacer. The study of the redox and optical properties of these chromophores and of reference compounds without dicyanovinyl units allows us correlate the electronic properties to the presence of the electron withdrawing groups and the molecular conformation. Comparison with calculated electronic structure shows that the construction of chromophores that consist of electron donating and accepting units does not always follow the simple rules that are generally used in the design of such molecules. The results show a subtle relation between the charge transfer character and the geometry of the molecules. In some cases this leads to significant contribution of charge transfer excitation to the absorption spectra of some chromophores while such contributions are completely absent in others.

A molecular dynamics study of the organic ionic plastic crystal tetramethylammonium dicyanamide is reported here. An all atom force field, based on CHARMM parameters, has been used, and calculations were carried out under NPT conditions at several temperatures ranging from the rigid lattice (200 K) up to well above the melt (600 K). The volume expansion, radial distribution functions and the onset of different rotational and translational motions has been simulated and are discussed both in terms of plastic crystals in general as well as compared to experimental results previously obtained for this particular system.

The microwave conductivity of trans- decalin solutions of the conjugated polymer poly(2,7-(9,9-bis(2-ethylhexyl)fluorene), PEHF, increases dramatically over tens to hundreds of nanoseconds subsequent to 5 ns pulsed irradiation. This is attributed to the reaction of the primary solvent electrons and holes with the polymer to form even more highly mobile electrons and holes on the polymer chains. Lower limits to the one-dimensional mobilities of electrons and holes on the polymer chains of ca 0.5 cm 2 /Vs are derived. Evidence is found for electron transfer to the polymer from CO 2 − .

Fast charge transport in conjugated polymers is essential for their application in opto-electronic devices. In the present paper, measurements and theoretical modeling of the mobility of excess charges along isolated chains of conjugated polymers in dilute solution are presented. Charge carriers were produced by irradiation of the polymer solution with 3-MeV electrons from a Van de Graaff accelerator. The mobilities of the charges along the polymer chains were obtained from time-resolved microwave conductivity measurements. The mobilities are strongly dependent on the chemical nature of the polymer backbone. Comparison of the experimental data with results from ab initio quantum mechanical calculations shows that the measured mobilities are strongly limited by torsional disorder, chemical defects and chain ends. Improvement of the structure of polymer backbones is therefore expected to significantly enhance the performance of these materials in ‘plastic electronics’.

The direct reaction field (DRF) model was developed for calculations of electronic properties of molecules in the condensed phase. In the DRF approach the electrons of (part(s) of a system is described with wavefunctions, the larger parts classically with point charges and polarizabilities. Leaving out the quantum-mechanical part(s) leads naturally to a polarizable force field. In this paper we demonstrate the usefulness of the DRF model for the study of many-body interactions in polar systems. We have calculated the many-body interactions in clusters of HF, H2O and urea in our classical polarization model and compared the results to ab initio calculations using large basis sets. We find that the results obtained using the classical model compare excellently to ab initio results.

The charge carrier mobility in bulk samples of α,ω-dihexylquaterthiophene has been determined as a function of temperature using the Pulse-Radiolysis Time-Resolved-Microwave-Conductivity and Thin Film Transistor (TFT) techniques. The mobility values obtained at room temperature were 0.01 cm 2 /Vs for both methods However upon cooling to 150 K the FET mobility decreases by an order of magnitude whereas the TRMC mobility remains almost constant. This behaviour is interpreted as an effect of the frequency of the electric field that is used in the experiments and could be described theoretically using an over-the-barrier hopping model for the mobility.

The charge carrier mobility in bulk samples of regioregular poly-3-hexylthiophene is determined from -100 to +140°C with the pulse-radiolysis time-resolved microwave conductivity technique. The lower limit to the mobility obtained increases only slightly with temperature in this range from 0.003 cm 2 /Vs to 0.01 cm 2 /Vs. However, the decay kinetics of the charge carriers is strongly dependent on temperature. This is attributed to changes in the effective domain size in which the charge carriers are able to move.