Cyclophanediene and Cyclophanetriene‐Based Conjugated Polymers

Abstract

Poly(p-phenylene vinylene)s (PPVs) and poly(arylene vinylene)s are key materials for a variety of applications ranging from organic light emitting diodes to fluorescent optical probes. Their syntheses, however, have been hampered by non-living or step-growth polymerization techniques. The development of functional-group tolerant olefin metathesis catalysts has enabled the use of living ring-opening metathesis polymerization (ROMP) of cyclophane monomers yielding PPVs and poly(p-phenylene-co-arylene vinylene)s in a living manner. Low dispersity and soluble PPVs are afforded with control over the number of repeat units with easy incorporation of different end-groups at their heads or tails. In this review, a comprehensive overview of tetrasubstituted and disubstituted alkyl and alkoxy containing [2.2]paracyclophane-1,9-diene, [2.2]metaparacyclophane-1,9-diene, [2.2.2]paracyclophane-1,9,17-triene, and benzothiadiazole-[2.2]paracyclophane-1,9-diene is provided. The high ring strain of these monomers enables efficient polymerizations with ruthenium initiators. A particular emphasis is on [2.2]paracyclophane-1,9-dienes as it is the most investigated class of polymerized cyclophanediene since initially reported 30 years ago. Additionally, applications for soft materials synthesized by ROMP are examined, highlighting easily accessed PPV copolymers and PPV block copolymers that can be phototriggered, as well as PPVs featuring supramolecular recognition units installed at their termini to afford orthogonally self-assembled architectures.

Bent and Twisted: Synthesis of an Alkoxy-Substituted (1,5)Naphthalene-paracyclophanediene

“…To synthesize 9 , the common synthetic route toward pCpd was followed . 1,5-Bis­(bromomethyl)-2,6-bis­(octyloxy)­naphthalene 4 , which was easily synthesized using a Blanc-like bromomethylation, was combined with dithiol 5 over 3 days in dilute conditions to afford dithia[3.3]­(1,5)­naphthalenoparacyclophane 6 .…”

“…Density functional theory (DFT) computations were performed for a truncated version of 9 to examine the effect of structure on the total strain energy of the paracyclophanediene (for a discussion of methods, see SI Section 6). The strain energy, Δ G strain , of 9 was computed to be 24.3 kcal/mol, significantly lower than that of 2 (39.4 kcal/mol) when computed by the same method . To elucidate the structural features that contribute to a lower strain energy, an energy decomposition of the total strain energy was performed, similar to the method described by Grimme for paracyclophane strain energies .…”

“…pCpds have gained popularity as monomers for the living ROMP to afford poly­( p -phenylene vinylene)­s (PPV), a conjugated polymer that has substantially contributed to the fundamental science of organic semiconductors . We hypothesized that 9 would be an ideal monomer to afford poly­(1,5-naphthylenevinylene- co - p -phenylenevinylene) 10 , a previously reported polymer that is hypsochromically shifted compared to PPV, , in a living manner due to the high ring strain and n -octyloxy side-chains necessary for solubilizing the conjugated polymer.…”

“…17 While altering the aromatic decks of pCp is common, dienes like pCpd have seen much less structural diversity due to the harsher reaction conditions required for their synthesis. 18 Compounds related to pCp and pCpd are [2.2]naphthalenophane and [2.2]naphthalenophane-1,13-diene, where both benzene moieties are replaced with naphthalene, which is typically substituted at the (1,4), 23 (1,5), 24 (2,6), 25,26 or (2,7) 27 positions. Mixing the arenes affords [2.2]naphthalenoparacyclophanes (such as 3), a highly strained class of cyclophane that has been studied by Haenel and Reiss.…”

“…Many applications have been found for pCp such as ligands for chiral catalysts used in stereoselective synthesis, , chiroptics and optoelectronics, ,− pharmaceuticals, , and materials science. ,− The much more strained structural analog of 1 is [2.2]­paracyclophane-1,9-diene (pCpd) 2 , which has ethynylene bridges instead of ethylene bridges, bringing the benzene decks closer together than in the parent compound 1 resulting in more-bent benzenes . While altering the aromatic decks of pCp is common, dienes like pCpd have seen much less structural diversity due to the harsher reaction conditions required for their synthesis …”