Design preparation and properties of regularly alternating conjugated low molecular weight copolymers based on thienylene-azomethine moietics

A series of low molecular weight copolymers, composed of a sequence of thienylenic (low energy gap) and phenylenic (high energy gap) residues linked together by azomethinic moieties, was prepared and extensively characterized. The semicrystalline materials, showing a weight loss of about 20% up to 450 °C, are soluble in H2SO4 and, when complexed with GaCl3, in CH3NO2. The molecular structure was derived from FT-IR, viscosity, 1H NMR and electron spin resonance analyses. The reversible complexation with either strong or Lewis acids allowed us to characterize the electronic properties of the oligomers in different conformations (red ↔ blue). An approximate structural model consistent with the experimental data (X-ray diffraction) is presented and discussed. The energy gaps (close to 2 eV) indicated a fully conjugated structure for the oligomers. Electronic localization effects are detected in the terms of the series with the longest thienylenic sequence, therefore indicating the realization of a quantum-dot polymeric structure. χ(3) values observed under resonance conditions are about 10−9 e.s.u.