Mechanochemical Reactivity of a 1,2,4‐Triazoline‐3,5‐dione‐Anthracene Diels‐Alder Adduct

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 adduct TAD‐An of 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 of TAD‐An to another Diels‐Alder adduct MAL‐An obtained from maleimide and anthracene. The susceptibility to undergo rDa reaction correlates well with bond energy, such that C−N bond containing TAD‐An degrades faster C−C bond containing MAL‐An because C−N bond is weaker than C−C bond. Specifically, the results from polymer degradation kinetics under pulsed ultrasonication shows that polymer containing TAD‐An has a rate constant of 1.59×10−5 min−1, while MAL‐An (C−C bond) has a rate constant of 1.40×10−5 min−1. Incorporation of TAD‐An in a crosslinked polymer network demonstrates the feasibility to utilize TAD‐An as an alternative force‐responsive probe to visualize mechanical damage where fluorescence can be “turned‐on” due to force‐accelerated retro‐Diels‐Alder reaction.