Electronically Governed ROMP: Expanding Sequence Control for Donor–Acceptor Conjugated Polymers

Abstract

Controlling the primary sequence of synthetic polymers remains a grand challenge in chemistry. A variety of methods that exert control over monomer sequence have been realized wherein differential reactivity, pre-organization, and stimuli-response have been key factors in programming sequence. Whereas much has been established in nonconjugated systems, π-extended frameworks remain systems wherein subtle structural changes influence bulk properties. The recent introduction of electronically biased ring-opening metathesis polymerization (ROMP) extends the repertoire of feasible approaches to prescribe donor–acceptor sequences in conjugated polymers, by enabling a system to achieve both low dispersity and controlled polymer sequences. Herein, we discuss recent advances in obtaining well-defined (i.e., low dispersity) polymers featuring donor–acceptor sequence control, and present our design of an electronically ambiguous (4-methoxy-1-(2-ethylhexyloxy) and benzothiadiazole-(donor–acceptor-)based [2.2]paracyclophanediene monomer that undergoes electronically dictated ROMP. The resultant donor–acceptor polymers were well-defined (Đ = 1.2, Mn > 20 k) and exhibited lower energy excitation and emission in comparison to ‘sequence-ill-defined’ polymers. Electronically driven ROMP expands on prior synthetic methods to attain sequence control, while providing a promising platform for further interrogation of polymer sequence and resultant properties.1 Introduction to Sequence Control2 Sequence Control in Polymers3 Multistep-Synthesis-Driven Sequence Control4 Catalyst-Dictated Sequence Control5 Electronically Governed Sequence Control6 Conclusions

Cyclophanediene and Cyclophanetriene‐Based Conjugated Polymers

“…[3,14] Synthe- sis of donor-acceptor polymers, however, are typically accomplished by poorly-controlled cross-coupling/polycondensation methods (or the use of iterative synthetic techniques) that do not lend themselves to the formation of high-molecular weight polymers. [34,35,88] Recent advances have been made toward living chain-growth polymerizations for donor-acceptor polymers with the newly reported BTD-pCpd. Incorporating BTD (an acceptor motif) with a substituted phenyl moiety (a donor motif) into a cyclophanediene enables living ROMP to access a donor-acceptor poly(p-phenylene-co-arylene vinylene).…”