Abstract:We present the synthesis and characterization of a new family of perfectly alternating conjugated polymers, obtained through different methodologies (Stille, Direct Arylation, and Horner–Wadsworth–Emmons polymerizations). The polymers comprise either 2,5‐dialkoxybenzene or benzodithiophene electron rich units, and 1,2,4,5‐tetrafluorobenzene as the electron‐deficient unit, eventually separated by a vinylene bridge, if suitable monomers and HWE polymerization procedures are used. As shown by NMR spectroscopy, th… Show more
“…Synthetic methodologies that achieve well‐defined conjugated polymers have received considerable attention owing to their ability to control lengths, sequences, and regioregularity. For applications in organic electronics, polymers typically comprise donor‐acceptor (D‐A) sequences that promote narrow band gaps . To date, methods to engineer D‐A conjugated polymers are generally step‐growth polymerizations (e.g., Pd‐catalyzed Stille condensation) that afford ill‐defined architectures and sequences, variable molecular weights, and high dispersities ( Đ ), which impede both crystallization and self‐assembly.…”
Reported are well‐defined donor‐acceptor alternating copolymers prepared using ring‐opening metathesis polymerization (ROMP). Unsymmetrical cyclophanedienes comprising electron‐donating (4‐methoxy‐1‐(2‐ethylhexyl)oxy)benzene (MEH) and electron‐accepting benzothiadiazole (BT) rings were synthesized from the corresponding [3.3]dithiaparacyclophanes. ROMP of the strained unsymmetrical and “electronically‐ambiguous” cyclophanedienes proceeded in a controlled manner in the presence of either Hoveyda–Grubbs II or Grubbs II initiator in wake of both steric and electronic encumbrance. The resulting polymers, comprising alternating BT and MEH‐PPV units, are achieved in molecular weights exceeding 20k with Đ values ranging from 1.1–1.4. The living nature of the polymerization is verified through the formation of rod‐coil and rod‐rod block copolymers. Our strategy to develop previously unrealized polymers from functional building blocks featuring a locked‐in D‐A unit is significant in a field striving to achieve well‐defined and sequence‐specific materials.
“…Synthetic methodologies that achieve well‐defined conjugated polymers have received considerable attention owing to their ability to control lengths, sequences, and regioregularity. For applications in organic electronics, polymers typically comprise donor‐acceptor (D‐A) sequences that promote narrow band gaps . To date, methods to engineer D‐A conjugated polymers are generally step‐growth polymerizations (e.g., Pd‐catalyzed Stille condensation) that afford ill‐defined architectures and sequences, variable molecular weights, and high dispersities ( Đ ), which impede both crystallization and self‐assembly.…”
Reported are well‐defined donor‐acceptor alternating copolymers prepared using ring‐opening metathesis polymerization (ROMP). Unsymmetrical cyclophanedienes comprising electron‐donating (4‐methoxy‐1‐(2‐ethylhexyl)oxy)benzene (MEH) and electron‐accepting benzothiadiazole (BT) rings were synthesized from the corresponding [3.3]dithiaparacyclophanes. ROMP of the strained unsymmetrical and “electronically‐ambiguous” cyclophanedienes proceeded in a controlled manner in the presence of either Hoveyda–Grubbs II or Grubbs II initiator in wake of both steric and electronic encumbrance. The resulting polymers, comprising alternating BT and MEH‐PPV units, are achieved in molecular weights exceeding 20k with Đ values ranging from 1.1–1.4. The living nature of the polymerization is verified through the formation of rod‐coil and rod‐rod block copolymers. Our strategy to develop previously unrealized polymers from functional building blocks featuring a locked‐in D‐A unit is significant in a field striving to achieve well‐defined and sequence‐specific materials.
“…Despite the wealth of methods, typical cross-coupling-based polymerizations afford higher dispersity and can lack control over sequence. 31 Recent focus has been placed on realizing well-defined (low dispersity) conjugated polymers. The advent of Kumada catalyst transfer polymerization (KCTP), 43 while still in its infancy, has equipped chemists with advanced tools for polymer synthesis and design.…”
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
“…E factor values for organic semiconductors are often in the excess of 10 4 , in some cases largely surpassing those for organic small molecules, which are active components of pharmaceutical formulations [20][21][22]. Our group has recently introduced a one-pot cascade methodology, comprising direct arylation (DHA) [23][24][25][26][27] and cross aldol condensations as the sequence of two alkalinemediated reactions in a single process. The DHA step, occurring regio-specifically on the 2-position of 3-thiopheneacetic acid, facilitates the subsequent cross aldol step, which completes the formation of an annulated aromatic ring.…”
The synthesis and characterization of four novel donor-acceptor-donor π-extended oligomers, incorporating naphtha(1–b)thiophene-4-carboxylate or benzo(b)thieno(3,2-g) benzothiophene-4-carboxylate 2-octyldodecyl esters as end-capping moieties, and two different conjugated core fragments, is reported. The end-capping moieties are obtained via a cascade sequence of sustainable organic reactions, and then coupled to benzo(c)(1,2,5)thiadiazole and its difluoro derivative as the electron-poor π-conjugated cores. The optoelectronic properties of the oligomers are reported. The novel compounds revealed good film forming properties, and when tested in bulk-heterojunction organic photovoltaic cell devices in combination with PC61BM, revealed good fill factors, but low efficiencies, due to their poor absorption profiles.
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