Conjugated Organic Polymers: Effects of Chirality on Aggregation and Optical Properties

Organic conjugated polymers are by far the most promising functional materials in view of applications in inexpensive and flexible electronic devices. Several prototypes of field-effect transistors (OFETs), light-emitting diodes (OLEDs), photovoltaic cells, and related devices based on organic materials have already been fabricated. The performances of such devices, depend on polymers’ primary structure, but to an even larger extent on their supramolecular organization. Therefore, the characterization and the control of the supramolecular arrangement of these systems constitute a crucial challenge in achieving advanced properties and functions of optoelectronic devices. The introduction of stereodefinite chiral elements in conjugated polymers has been exploited as a structural modification able, to generate a regular intermolecular chiral orientation of the rigid polymer chains during aggregation processes. Several PPVs and PPEs functionalized with chiral groups with controlled stereochemistry, were prepared and characterized. ECD spectroscopy has proved to be an optimal technique to study the presence of chiral aggregated species and to investigate the aggregation properties both in the solid state and in solution. First of all, MEH-PPV and MEH-PPE aggregation properties have been investigated focusing on the effect of the configuration of the stereogenic center. Moreover several novel different PPEs functionalized with α-aminoacids were prepared evidencing the crucial role of hydrogen bonding leading, together with the steric hinderance proper of the aminoacid, to different aggregates as function of the aminoacidic fragment. These products are relatively easy to prepare, not expensive and functionalizable with any aminoacidic derivates, so they represent a really promising class of materials.