Mechanochemical unzipping of insulating polyladderene to semiconducting polyacetylene

Abstract

Biological systems sense and respond to mechanical stimuli in a complex manner. In an effort to develop synthetic materials that transduce mechanical force into multifold changes in their intrinsic properties, we report on a mechanochemically responsive nonconjugated polymer that converts to a conjugated polymer via an extensive rearrangement of the macromolecular structure in response to force. Our design is based on the facile mechanochemical unzipping of polyladderene, a polymer inspired by a lipid natural product structure and prepared via direct metathesis polymerization. The resultant polyacetylene block copolymers exhibit long conjugation length and uniform trans-configuration and self-assemble into semiconducting nanowires. Calculations support a tandem unzipping mechanism of the ladderene units.

Mechanical Force Induces Ylide‐Free Cycloaddition of Nonscissible Aziridines

“…These polymers have found several applications, including in structure engineering, catalysis, sensors, patterning, recycling of resources, materials transfer, and gating to regulate other reactions . Such systems can activate covalent and coordination bonds,– and change the electrical and optical properties of polymers . The activation of mechanophores also allows one to steer chemical reactions toward routes that are inaccessible under traditional thermal and photochemical conditions –.…”

“…The common approach for mechanochemical studies is to harness vulnerable chemical structures that have weak bond energies or high strains as mechanophores. Thus, most mechanophores usually exhibit irreversible bond scission upon exposure to mechanical forces . A limited number of mechanophores often undergoes isomerization (see Figure A for examples) …”

“…Thus, most mechanophores usually exhibit irreversible bond scission upon exposure to mechanical forces. [9,12] A limited number of mechanophores often undergoes isomerization (see Figure 1 A for examples). [2c,f] Highly strained ring structures, like gem-dihalocyclopropanes [13] and epoxides, [14] are attractive mechanophores.…”

Enzymatic construction of highly strained carbocycles

“…The intrinsic energy of these strained structures can also be relieved in response to exogenous force, which leads to radical changes in physical properties ( e.g . conductivity), a feature highly desirable for stimulus-responsive materials (9, 10). …”

The Intrinsic Mechanochemical Reactivity of Vinyl‐Addition Polynorbornene

“…Mechanophore activation can also be used as as ynthetic strategy to lower the thermal or photochemical energy input required for known reaction pathways,such as ring-opening isomerization. Examples of these customdesigned multimechanophore polymers include those containing strained rings along the polymer backbone,s uch as cyclopropanes [5,[13][14][15] and cyclobutanes, [16] which have been shown to exhibit high mechanochemical activity. Additionally,s mall deviations in mechanophore location relative to the center of the polymer chain may also affect activation efficiency.…”