Conjugated oligomers with alternating heterocycles from a single monomer: synthesis and demonstration of electroluminescence

Conjugated oligomers based on two different heterocycles are typically prepared by step growth polycondensation cross-coupling methods from two monomers X-Cycle1-X and M-Cycle2-M with no control of the regioselectivity. In this work, we used a new synthetic strategy that involves an extremely chemoselective reaction of a dielectrophilic compound, X1-Cycle1-X2, with a dinucleophilic component, M1-Cycle2-M2, under Stille conditions. The resulting monomers, X1-Cycle1-Cycle2-M2 are di-heterocyclic push–pull monomers that still contain a nucleophilic site (boronic acid) and electrophilic site (bromide) and are set up for a controlled polymerization under Suzuki conditions. In this way, two semiconducting oligomers, based on thiophene/benzene and thiophene/pyridine motifs were synthesized. Both oligomers were characterized in terms of their thermal, electrochemical, absorption, emission and electroluminescence properties.