Synthesis and Photophysics of Fully π-Conjugated Heterobis-Functionalized Polymeric Molecular Wires via Suzuki Chain-Growth Polymerization

Abstract

We present a fast and efficient in situ synthetic approach to obtain fully π-conjugated polymers with degrees of polymerization up to 23 and near quantitative (>95%) heterobis-functionalization. The synthesis relies on the key advantages of controlled Suzuki chain-growth polymerization: control over molecular weight, narrow polydispersity, and ability to define polymer end groups. The first end group is introduced through the initiator metal complex tBu(3)PPd(X)Br, while the second end group is added by quenching of the chain-growth polymerization with the desired boronic esters. In all cases, polymers obtained at 50% conversion showed excellent end group fidelity and high purity following a simple workup procedure, as determined by MALDI-TOF, GPC, and (1)H and 2D NMR. End group functionalization altered the optoelectronic properties of the bridge polymer. Building on a common fluorene backbone, and guided by DFT calculations, we introduced donor and acceptor end groups to create polymeric molecular wires exhibiting charge transfer and energy transfer as characterized by fluorescence, absorption, and transient absorption spectroscopy as well as by fluorescence lifetime measurements.