Thermally bisignate supramolecular polymerization

Abstract

One of the enticing characteristics of supramolecular polymers is their thermodynamic reversibility, which is attractive, in particular, for stimuli-responsive applications. These polymers usually disassemble upon heating, but here we report a supramolecular polymerization that occurs upon heating as well as cooling. This behaviour arises from the use of a metalloporphyrin-based tailored monomer bearing eight amide-containing side chains, which assembles into a highly thermostable one-dimensional polymer through π-stacking and multivalent hydrogen-bonding interactions, and a scavenger, 1-hexanol, in a dodecane-based solvent. At around 50 °C, the scavenger locks the monomer into a non-polymerizable form through competing hydrogen bonding. On cooling, the scavenger preferentially self-aggregates, unlocking the monomer for polymerization. Heating also results in unlocking the monomer for polymerization, by disrupting the dipole and hydrogen-bonding interactions with the scavenger. Analogous to 'upper and lower critical solution temperature phenomena' for covalently bonded polymers, such a thermally bisignate feature may lead to supramolecular polymers with tailored complex thermoresponsive properties.

Supramolecular Polymers – we've Come Full Circle

“…Two illustrating examples have been presented recently. Firstly, supramolecular polymerization of a H‐bonding porphyrin polymerization in a hydrocarbon solvent containing a minute amount of a H‐bond scavenging alcohol shows distinct pathways in a thermally bisignate supramolecular polymerization (Figure ) . Secondly, minute amounts of molecularly dissolved water molecules in apolar solvents, like methylcyclohexane, become part of the supramolecular polymer at lower temperatures, due to specific H‐bonding interaction between the monomer and water …”

A Competing Hydrogen Bonding Pattern to Yield a Thermo‐Thickening Supramolecular Polymer

“…This has contributed to the development of innovative catalysts, [6,7] fluorescent systems, [8,9] self-healing materials, [10,11] and gels, [12,13] among other potential applications.O ne fascinating consequence of the dynamic character of supramolecular assemblies is the capability of molecular building blocks to assemble into distinct thermodynamically or kinetically stable nanostructures. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes. [27][28][29] This pathway complexity in the aggregation ability of the monomers is usually revealed by spectroscopic techniques that identify the structural differences in the assemblies at the nano or mesoscale (for example,kinetics of aggregation, helicity,s tacking mode,c onformation).…”

“…[14] An umber of studies describe the possibility of selecting one of these nanostructures by carefully controlling the conditions of aggregation, namely,t ime, [15][16][17][18] concentration, [19] temperature, [20] solvent, [21][22][23][24][25] and diffusion, [26] or by tuning the nature of the monomer. [20] Thei ntroduction of competing interactions in the design of as upramolecular assembly is al ogical approach to create pathway complexity.I np ractice,t his can be done through solvents [21,34,35] and additives [19,33,36,37] or by introducing functional groups that can interfere with the main sticker.O ften, this latter approach will weaken the main assembly, [38,39] but it can also lead to an ew structure with ac ompetitive thermodynamic stability. [30,31] However,achange in the properties of the supramolecular assemblies at the macroscale has been reported for very few cases.…”

“…[30,31] However,achange in the properties of the supramolecular assemblies at the macroscale has been reported for very few cases. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes.…”

“…[20,32] In fact, the properties of SPs can be considerably diversified when they form in competition with other assemblies.I ndeed, pathway complexity can be responsible for unusual behaviors such as aself-assembly that is triggered by dilution, [19] or by both increasing or decreasing the temperature. [20] Thei ntroduction of competing interactions in the design of as upramolecular assembly is al ogical approach to create pathway complexity.I np ractice,t his can be done through solvents [21,34,35] and additives [19,33,36,37] or by introducing functional groups that can interfere with the main sticker.O ften, this latter approach will weaken the main assembly, [38,39] but it can also lead to an ew structure with ac ompetitive thermodynamic stability. [20] Thei ntroduction of competing interactions in the design of as upramolecular assembly is al ogical approach to create pathway complexity.I np ractice,t his can be done through solvents [21,34,35] and additives [19,33,36,37] or by introducing functional groups that can interfere with the main sticker.O ften, this latter approach will weaken the main assembly, [38,39] but it can also lead to an ew structure with ac ompetitive thermodynamic stability.…”