Changing Mechanical Strength in Cr(III)- Metallosupramolecular Polymers with Ligand Groups and Light Irradiation

Abstract

We have demonstrated the ability to control the mechanical properties of metallosupramolecular materials via choice of ligand binding group, as well as with external light irradiation. These photoresponsive Cr(III)-based materials were prepared from a series of modified hydrogenated poly(ethylene-co-butylene) polymers linked through metal-ligand interactions between a Cr(III) metal center and pyridyl ligand termini of the polymers. The introduction of these Cr(III)-pyridine bonds gave rise to new mechanical and optical properties of the polymer materials. Depending on the type of pyridyl ligand, density functional theory calculations revealed changes in coordination to the Cr(III), which ultimately led to materials with significantly different mechanical properties. Electronic excitation of the Cr(III) materials with 450 and 655 nm CW lasers (800 mW/cm(2)) resulted in generation of excited state photophysical processes which led to temporary softening of the materials up to 143 kPa (41.5%) in storage modulus (G') magnitude. The initial mechanical strength of the materials was recovered when the light stimulus was removed, and no change in mechanical properties was observed with light irradiation where there was no absorbance by the Cr(III) moiety. These materials demonstrate that introduction of metal-ligand bonding interactions into polymers enables the design and synthesis of photoresponsive materials with tunable optical-mechanical properties not seen in traditional polymeric materials.

Recyclable Cu(II)‐Coordination Crosslinked Poly(benzimidazolyl pyridine)s as High‐Performance Polymers

“…In the addition of Cu 2+ from 2.0 × 10 −6 to 1.0 × 10 −5 m , the λ max underwent a slight redshift to 441 nm along with a distinct enhancement in absorbance, which was ascribed to the charge transfer between the electron accepting Cu 2+ and electron donating pyridine units . The results indicated the formation of MeBIP–Cu(II) coordination bonds …”

“…Ostrowski and co‐workers have developed a series of metal‐coordination crosslinked soft materials. The mechanical and optoelectronic properties of such materials could be successfully tuned via a supramolecular coordination strategy . Inspired by the findings mentioned above, in this paper, our aim is to use the noncovalent metal‐coordination interaction as crosslinking for synthesizing an infusible and insoluble stiff crosslinked high‐performance polymer.…”

“…The mechanical and optoelectronic properties of such materials could be successfully tuned via a supramolecular coordination strategy. [34] Inspired by the findings mentioned above, in this paper, our aim is to use the noncovalent metal-coordination interaction as crosslinking for synthesizing an infusible and insoluble stiff crosslinked high-performance polymer. Meanwhile, we expect that this crosslinking can be further removed via external stimuli to recover the linear polymer, which could endow the resulting material with a recyclable behavior.…”

Supramolecular elastomers: Switchable mechanical properties and tuning photohealing with changes in supramolecular interactions

“…It is a challenge to make these materials have stimuli‐responsive properties, however, since the key design feature of this class of supramolecular materials is based on complex interactions of multiple hydrogen‐bonding motifs, which suffer from non‐ideal photochemical properties such as a lack of visible light absorption. This limits them as stimulus‐responsive materials, significantly reducing the capacity to respond to light stimuli . Alternatively, in supramolecular materials using metal coordination motifs, the metal coordination center can also serve as chromophore so that visible light irradiation can be used to control the metal–ligand interactions …”

“…This limits them as stimulus‐responsive materials, significantly reducing the capacity to respond to light stimuli . Alternatively, in supramolecular materials using metal coordination motifs, the metal coordination center can also serve as chromophore so that visible light irradiation can be used to control the metal–ligand interactions …”