A Simple Mechanochromic Mechanophore Based on Aminothiomaleimide

Abstract

Mechanochromic mechanophores have promising applications in stress sensing and damage detection. Here we report a simple mechanofluorochromic mechanophore based on aminothiomaleimide (ATM). Poly­(methyl acrylate) containing this mechanophore (ATM-PMA) was synthesized by atom transfer radical polymerization (ATRP) using an ATM-derived difunctional initiator. To investigate its mechanofluorochromism, the solution of ATM-PMA was subjected to ultrasonication, and size exclusion chromatography (SEC) and fluorescence spectroscopy were employed to monitor the changes in molecular weight and fluorescence emission. The results showed that the molecular weight of ATM-PMA decreased upon ultrasonication, accompanied by a shift of fluorescence emission from bright yellow to light blue. This mechanophore of a simple functional group of ATM has great potential to be used in mechanochromic polymer materials.

Quantifying Activation Rates of Scissile Mechanophores and the Influence of Dispersity

“…The rate of ultrasound-induced polymer chain scission, which indirectly reports on the activity of a scissile mechanophore located near the chain midpoint, is routinely characterized using a linearization function applied to time-dependent changes in average molecular weight. ,,− The theoretical eq , which was originally developed to describe random polymer degradation processes, , was applied by Sato and Nalepa to the ultrasonic degradation of cellulose derivatives as early as 1978 where M n, t and M n,0 are the number-average molecular weight at time t and t = 0, respectively, and k ′ is the apparent rate constant for polymer chain scission. While values of k ′ with units of mol kg –1 min –1 are often reported in the literature, ,,− ,, the actual rate constant from this linearization analysis is provided by eq where k L has units of min –1 after adjusting for the molecular weight of the polymer repeat unit, m 0 .…”

Concurrent and Mechanochemical Activation of Two Distinct and Latent Fluorophores via Retro-Diels–Alder Reaction of an Anthracene–Aminomaleimide Adduct

“…Compared to traditional polymer mechanochemistry that is typically destructive, modern polymer mechanochemistry can be productive and effective by introducing force-sensitive chemical groups called mechanophores . Externally applied mechanical stress is transduced to mechanophores via covalently tethered polymer chains, resulting in selective and specific chemical transformation of the mechanophores, which has been shown to either reveal novel mechanochemical phenomena or realize desired material functions, e.g., changing color, − regulating chemical reactions, − releasing small molecules, − activating drugs, , switching polymer conductivity, − etc. , Especially, mechanochromic mechanophores that alter absorption and/or emission color in response to applied mechanical stress have been capturing increasing research interest owing to their potential applications in stress sensing and damage detection. − …”

Fluorogenic Mechanophore Based on Dithiomaleimide with Dual Responsiveness

“…Meanwhile, the ultrasonication-induced chain scission was accompanied by a corresponding increase in the fluorescence emission peak at 510 nm, and the final solution of PMA-1 after 120 min of ultrasonication showed strong and green emission under 365 UV light, in contrast to the solution prior to ultrasonication that was weakly fluorescent, as shown in Figure 4c. This suggested fluorescence turn-on of the dansyl fluorophore, which was because the C−S bond (not adjacent to the maleimide core) was believed to break upon mechanochemical activation as predicted by the CoGEF method, 30,47 leading to the dissociation of the dansyl group from the quencher of maleimide. To be mentioned, the PMA-1 solution exhibited a ∼5.3-fold increase in the emission peak intensity at 510 nm after 120 min of ultrasonication, compared to that prior to ultrasonication (Figure 4d).…”

“…Polymer mechanochemistry has been capturing increasing research interest and has experienced a rapid growth over the past two decades, thanks to the innovation and development of mechanophores that are force-sensitive chemical groups . Generally, mechanophores are covalently incorporated into polymer backbones and undergo selective and specific chemical transformation under applied mechanical stress, which enables desired material functions, including regulation of chemical activity, − release of small molecules/drugs, − switch in polymer conductivity, − etc . − Development of mechanochromic mechanophores that change color or luminescence upon mechanochemical activation has become a research focus − owing to their potential applications in mechanosensing and damage detection in polymers. − A typical mechanochromic mechanophore changes its color through force-induced chemical transformation into one or two new chromophores/fluorophores. Interestingly, however, Weder and co-workers developed a fluorogenic mechanophore based on a rotaxane with a fluorophore-carrying macrocycle and a dumbbell-shaped molecule containing a matching quencher and incorporated it into a polyurethane elastomer, the fluorophore was turned on upon deformation of the polymer due to its spatial separation from the quencher and became quenched again after strain release .…”

“…Furthermore, it has been reported by Baker and co-workers that the dansyl fluorophore can be quenched when attached via a thioether bond to the maleimide core as well . Therefore, we expect that fluorogenic mechanophores can be designed based on thiomaleimides of which the relatively weak C–S bond is believed to break upon mechanical activation despite the lack of direct structural evidence of the mechanochemical products. ,− To develop a proof-of-concept, we choose dansyl-dithiomaleimide (Dansyl-DTM) as the fluorophore-quencher pair. As shown in Figure , it is assumed that the C–S bond can be selectively cleaved under applied mechanical force, resulting in the removal of the maleimide conjugation and thus turn-on of the dansyl fluorophore.…”