Edsko E. Havinga

Chiroptical Properties of Regioregular Chiral Polythiophenes

Abstract The synthesis and (chir)optical properties of a highly regioregular optically active 3-substituted polythiophene are reported. Using the McCullough method a regioselectivity of more than 98% is found for the head-to-tail coupling in 3-[2-((S)-2-methylbutoxy)ethyl]polythiophene 1. Contrary to the small effects observed for the regiorandom analogue 2, made by FeCl3-polymerization, 1 shows a strong induced optical activity in its π-π* transition, provided the polymer is in its almost coplanar associated form. This association with a strong conformational rigidity, a prerequisite for a stable chirality from a helical structure of 1, is found in poor-solvents as well as in the solid state. In a good solvent like CHCl3, the disordered non-planar structure is optically inactive in its backbone. The transfer to an associated form is accompanied with solvatochromism and thermochromism in absorption, while significant changes in fluorescence behaviour and in the circular dichroism spectra are observed. All...

Oligoheterocycles by the Stille-coupling reaction

In this paper the applicability of the Stille-coupling reaction for the synthesis of a variety of oligoheterocyclic compounds is presented. Despite some experimental difficulties (destannylation, purification) we have been able to synthesize a wide variety of compounds based on combinations of pyrrole, thiophene and benzene units in reasonable yields.

π-Dimers of pyrrole-thiophene oligomer cation radicals

The redox states of phenyl end-capped oligomers containing pyrrole and thiophene units are characterized with optical absorption and EPR spectroscopy. The spectra give direct evidence for the π-dimerization of the corresponding cation radicals in solution.