Functional conjugated organic oligomers and polymers constitute an interesting group of materials for their application in optoelectronic devices. The combination of the mechanical properties (i.e. plasticity and processability) with their tuneable electrical and optical properties (conductivity, photo- and electroluminescence) makes them very attractive components, allowing for low-cost flexible thin films light-emitting diodes (LEDs), lasers, displays, photovoltaic cells, detectors or field-effect transistors (FETs). In the last 20 years, something that emerged as a promising field for new materials and applications has evolved to real industry with commercial products on the market.

The performance of the organic-based devices relies on several complementary processes which take place in the active layer, such as optical absorption, energy migration and emission as well as charge generation, transport and recombination. In order to understand these processes, it is necessary to acquire a deep knowledge in the nature and properties of the materials in the active layer. This concerns the intrinsic molecular properties, i.e. nature and (torsional) flexibility of the molecular backbone, effective conjugation length and substitution pattern, but also the specific arrangement of the molecules in the layer, which in turn is controlled by their intrinsic properties. The systematization of the relationship between the molecular structure, and their electronic and optical properties is thus the starting point in the rational design of new materials with improved properties. The design of materials prior to synthesis has become an important subject in material science, where theory works hand in hand with chemistry, physics, and device technology in a multidisciplinary approach. The last 10 years saw a rapid evolvement of quantum-chemical methods for the reliable prediction of material properties together with increasing computing capabilities. However, meaningful results require a profound knowledge on the possibilities and limits of the different quantum-chemical methods, only provided by specialists, but working in an interdisciplinary environment. My methodological toolbox ranges from cost-efficient semi-empirical methods, via density-functional based approaches, to different ab-initio methods, making use of various quantum-chemical packages to exploit the full spectrum of reliable theoretical description.

With the knowledge of the appropriate quantum-chemical method at hand, it is possible to determine accurately neutral and charged species of conjugated organic molecules in their ground and excited state. This concerns the molecular geometry and conformation, IR and Raman vibrational spectra, orbital energy and topology, electron affinity and ionization potentials, energy as well as the intensity and vibronic properties of electronic transitions. Similarly, intermolecular effects can be treated to extract excitonic and electronic couplings for modelling solid state spectra, and energy and charge transport properties, thus becoming an indispensable instrument in material design.

Collaborators

• Johannes Gierschner - Instituto Madrileño de Estudios Avanzados (IMDEA)

Work team

• Junquing Shi - Instituto Madrileño de Estudios Avanzados (IMDEA)

Investigation activities