Synthesis and Characterization of Fully Conjugated Donor-Acceptor-Donor Triblock Copolymers

A synthetic approach is established to provide a monofunctional telechelic poly(3-octylthiophene) (P3OT) bearing a single bromine-substituted end group that is of potential use in the preparation of well-defined block copolymers. Telechelic P3OT was prepared via a chain growth process by a catalyst-transfer condensation polymerization (CTCP) of 5-bromo-4-octyl-2-thienylmagnesium iodide initiated by a phenylnickel(H) initiator. Optimization of the conditions for quenching the reaction allowed for the installation an a-bromo functionality at the terminus of the polymer. We demonstrate the utility of this well-defined monofunctional polymer, Ph-P3OT-Br, by coupling it to a poly(quinoxaline) (PQ) bearing boronate ester end groups to provided a new class of donor-acceptor-donor (D-A-D) triblock copolymers. The formation of the triblock copolymers was confirmed by gel-permeation chromatography (GPC) and (1)H NMR spectroscopy. The optical properties of the polymers were investigated using UV-visible absorption and fluorescence spectroscopy. Efficient quenching of the fluorescence from the individual blocks of the triblock copolymers is consistent with the occurrence of electron transfer. AFM images illustrate a nanoscale phase separation of the electron-rich P3OT and electron-poor PQ blocks.