Sensitive Mechanocontrolled Luminescence in Cross-Linked Polymer Films

Abstract

Direct translation of mechanical force into changes in chemical behavior on a molecular level has important implication not only for the fundamental understanding of mechanochemical processes, but also for the development of new stimuli-responsive materials. In particular, detection of mechanical stress in polymers via non-destructive methods is important in order to prevent material failure and to study the mechanical properties of soft matter. Herein, we report that highly sensitive changes in photoluminescence intensity can be observed in response to the mechanical stretching of cross-linked polymer films when using stable, (pyridinophane)Cu-based dynamic mechanophores. Upon stretching, the luminescence intensity increases in a fast and reversible manner even at small strain (< 50%) and applied stress (< 0.1 MPa) values. Such sensitivity is unprecedented when compared to previously reported systems based on organic mechanophores. The system also allows for the detection of weak mechanical stress by spectroscopic measurements or by direct visual methods.<br>

Triboluminescence of a new family of CuI–NHC complexes in crystalline solid and in amorphous polymer films

“…Due to our interest in exploring mechanoresponsive materials such as polymer lms modied with co-polymerized photoluminescent metal complexes, 25 we decided to see if TL properties can also be observed when these triboluminescent Cu(NHC) complexes were blended into amorphous polymer lms. Using polymer lms may provide a convenient way to make bulk mechanoresponsive material or coating via simple synthetic methods, avoiding the limited repeatability and fabrication method limitations associated with the use of a crystalline solid.…”

“…This is in contrast to previously reported NHC Cu I complexes cross-linked into elastomeric, stretchable polybutylacrylate lms, which do not show detectable triboluminescence. 25 Thus, these ndings represent the rst example of Cu complexes that display TL properties when simply blended into amorphous polymer lms. 53 There are several reports on TL polymers lms containing Eu complexes.…”

“…We previously synthesized a series of photoluminescent (PL) and air-stable Cu-NHC complexes containing N4 pyridinophane ligands, which can be cross-linked into polybutylacrylate lms. 25 The resulting Cu-containing polymers enable sensitive detection and visualization of mechanical stress via reversible changes in PL intensity when the elastic lm is stretched under UV light irradiation (Fig. 1).…”

From Molecules to Polymers—Harnessing Inter‐ and Intramolecular Interactions to Create Mechanochromic Materials

“…[176] Finally, these mechanoresponsive complexes were also used as cross-linkers in poly(butyl acrylate) (PBA), and spectroscopic analysis of samples during deformation showed that stresses as low as 0.1 MPa could be detected, providing further evidence for the sensitivity of the organometallic complexes to mechanical stimuli. [177] Moreover, the emission wavelength of [CuN 4 -NHC](BF 4 ) was successfully tuned by modifying the excited state geometry, i.e., by employing an NHC ligand with bulky diisopropyl (DIP) moieties. [178] PUs in which this complex was covalently integrated responded to tensile elongation by an increase in PL intensity as well as a blue shift of the emission band, which was attributed to an increasing separation of the BF 4 − counterion from the complex as the surrounding polymer matrix deformed.…”

Activation of a Copper Biscarbene Mechano‐Catalyst Using Single‐Molecule Force Spectroscopy Supported by Quantum Chemical Calculations

“…[8] However, the exact force acting on a mechanophore is difficult to ascertain, as many factors during cavitation or within a material influence the transmittance of the force to the mechanophore, such as the molecules overall rigidity, [3f,9] the length of attached residues [10] or the material's morphology. [11] Thus, recent activities on metallocenes, [7] Cu-pyridine, [12] and BÀ N bonds [13] demonstrated metal/ligand-cleavage in polymeric bulk-systems or in solution, which finally did not allow for a precise, direct quantification of the individual metal/ligandbond upon mechanical stressing.…”