Regioisomer-Specific Mechanochromism of Naphthopyran in Polymeric Materials

Abstract

Transformation of naphthopyran into a colored merocyanine species in polymeric materials is achieved using mechanical force. We demonstrate that the mechanochemical reactivity of naphthopyran is critically dependent on the regiochemistry, with only one particular substitution pattern leading to successful mechanochemical activation. Two alternative regioisomers with different polymer attachment points are demonstrated to be mechanochemically inactive. This trend in reactivity is accurately predicted by DFT calculations, reinforcing predictive capabilities in mechanochemical systems. We rationalize the reactivity differences between naphthopyran regioisomers in terms of the alignment of the target C-O pyran bond with the direction of the applied mechanical force and its effect on mechanochemical transduction along the reaction coordinate.

High-intensity focused ultrasound-induced mechanochemical transduction in synthetic elastomers

“…The advantage of the proposed method over existing triggering methods is the capability to achieve spatiotemporal control of mechanophore activation. In particular, while previous studies have demonstrated mechanochemical activation in bulk polymers using compression and tension (3,4,8,45), the HIFU-based triggering system demonstrated here is a remote energy source capable of localizing the region of activation and triggering polymer mechanochemistry noninvasively. These advances enable mechanoactivation of two different mechanophore systems.…”

“…In this work, we evaluate the ability of HIFU to trigger polymer mechanochemistry in a polydimethylsiloxane (PDMS) elastomeric network through mechanical deformation. Our group has previously reported naphthopyran (NP) as a colorless mechanophore that undergoes electrocyclic ring opening, generating an orange-colored merocyanine in response to mechanical force (4). The visible color change associated with NP mechanoactivation provides a simple readout for initial investigations of the HIFU-triggered polymer mechanochemistry.…”

“…Particularly, mechanophores, i.e., mechanically sensitive molecules, have attracted attention due to their role in eliciting various chemical transformations in polymers (2). Extensive work in molecular design has revealed a rich library of mechanophores, which when subjected to mechanical stress undergo selective bond cleavage to unveil color change (3,4), fluorescence (5), new reactive functionality (6), catalytic activity (7), light emission (8), and small-molecule release (9), among other responses. The ability of mechanochromic mechanophores to "visualize" the mechanical response to applied force provides insight for identifying the damage location and the material state in polymeric materials.…”

“…Of particular importance to extending functionality of these mechanophores is the development of novel force-control tools capable of noninvasively triggering their activation. Mechanochemical responses have been observed when mechanical energy is applied to bulk-phase materials via mechanisms such as compression (10, 11), tension (3,4), and shock wave (12,13), or to solution-phase polymers and polymer interfaces via ultrasonic cavitation (3,14,15). The ability to access a wide range of chemical reactivity via mechanical force has led researchers to consider the applicability of polymer mechanochemistry in biomedical applications as a platform for drug delivery (16)(17)(18)(19) or sensing and selfreporting materials (20)(21)(22).…”

Tuning the Photophysical Properties of Symmetric Squarylium Dyes: Investigation on the Halogen Modulation Effects

“…[12] Fluorochromicm aterials with reversiblec olor changet riggered by external stimuli are an important category of smart materials. [13] Up to now,s everalt ypes of fluorochromic materials have been developed such as photochromic, [14] electrochromic, [15] thermochromic, [16] mechanochromic, [17] solvatochromic, [18] and vapochromic [19] materials. Among them, mechano-chromic materials with reversiblef luorescence change by mechanical stress have made rapid progress.…”