Highly luminescent polymer single crystals with anisotropic optical and electronic properties from appropriately designed, defect-free regioregular polythiophenes

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Correlations of thin film morphology with the resulting opto-electronic properties of organic electronic devices are often reported in the literature. However, the interference of several parameters is generally prevalent. Hence, precise structure-function relationships and the identification of the influence of individual parameters have remained elusive, and therefore the interpretation of opto-electronic properties of especially semi-crystalline conjugated polymers is complicated due to the presence of a multitude of possible morphologies consisting of crystalline and amorphous domains. Crystallization of polymers leads to lamellar crystals of various degrees of order. Here, we aim at reducing the complexity of structural features by basing our studies on polymeric single crystals made from defect-free, narrow distributed and regioregular polythiophenes. In such single crystals, the chains are ordered across all relevant length-scales. The main aims of this interdisciplinary projekt between polymer chemistry and experimental physics can be summarized as follows:1.The synthesis of defect-free poly(dialkylphenylthiophene) (PDAPT), which entails the controlled Kumada Catalyst Transfer Polycondensation (KCTP) of sterically hindered monomers as well as its variant of external initiation. To this end we will synthesize and introduce nickel complexes with hemilabile, mixed P,N ligands to transfer the good polymerization performance known so far to monomers with sterically hindered side chains. The choice of PDAPT lies in its special crystal structure: No pi-pi interactions are possible because of the unique side-chain pattern, which is in contrast to the generally observed pi-pi-stacking in polythiophenes, e.g. P3HT.2. Defect-free P3HT and defect-free PDAPT will be crystallized into single crystals employing self-seeding. The influence of experimental and molecular parameters such as time, temperature, concentration, molecular weight, polydispersity, side chain length, and pi-pi-interactions on the size, shape and perfection of the resulting single crystals will be elucidated.3.The anisotropic optoelectronic properties of all single crystals will be investigated as a function of the crystal direction. This entails absorption, photoluminescence, charge carrier mobility and exciton diffusion lengths, which will be systematically determined as a function of unit cell direction for a series of P3HT (pi-pi stacking) and PDAPT (no pi-pi stacking possible) polymers differing in molecular weight and side chain. One crucial point will be the influence of pi-pi interactions on charge transport. This will be resolved by comparing PDAPT with P3HT.