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An electrochemical coupling between carboxylic acids and penta uorophenol (PFP–OH) to access synthetically versatile penta uorophenyl (PFP) esters has been developed. Novel reactivity of PFP–OH was turned on by modulating its oxidation state, leveraging both its native O-nucleophilicity and its latent, oxidation-induced C-electrophilicity to promote a unique cascade of nucleophilic aromatic and acyl substitutions. Its esteri cation with acids was thus achieved for the rst time without exogenous dehydrating agents. The acidity of PFP–OH and the oxidizability of its conjugate base enabled its mild and selective activation via deprotonation–oxidation, readily affording PFP esters that are useful in many applications (peptide synthesis, chemical biology, etc.) and that contain redox-sensitive functional groups. Finally, we verified in a unified forum that an amino-acid-derived PFP ester can be converted into a range of acyl-substitution products while retaining key stereochemical information, and we demonstrated that PFP esters have excellent stability to hydrolysis, comparing favorably even to N-hydroxysuccinimidyl (NHS) esters. 

Abstract Force‐responsive molecules that produce fluorescent moieties under stress provide a means for stress‐sensing and material damage assessment. In this work, we report a mechanophore based on Diels‐Alder adductTAD‐Anof 4,4′‐(4,4′‐diphenylmethylene)‐bis‐(1,2,4‐triazoline‐3,5‐dione) and initiator‐substituted anthracene that can undergo retro‐Diels‐Alder (rDA) reaction by pulsed ultrasonication and compressive activation in bulk materials. The influence of having C−N versus C−C bonds at the sites of bond scission is elucidated by comparing the relative mechanical strength ofTAD‐Anto another Diels‐Alder adductMAL‐Anobtained from maleimide and anthracene. The susceptibility to undergo rDa reaction correlates well with bond energy, such that C−N bond containingTAD‐Andegrades faster C−C bond containingMAL‐Anbecause C−N bond is weaker than C−C bond. Specifically, the results from polymer degradation kinetics under pulsed ultrasonication shows that polymer containingTAD‐Anhas a rate constant of 1.59×10⁻⁵ min⁻¹, whileMAL‐An(C−C bond) has a rate constant of 1.40×10⁻⁵ min⁻¹. Incorporation ofTAD‐Anin a crosslinked polymer network demonstrates the feasibility to utilizeTAD‐Anas an alternative force‐responsive probe to visualize mechanical damage where fluorescence can be “turned‐on” due to force‐accelerated retro‐Diels‐Alder reaction.