Mechanoresponsive luminescent (MRL) hydrogels, which convert mechanical stimuli into detectable optical signals, have attracted significant attention in fields of flexible sensing and damage monitoring. The integration of mechanochromic mechanophores with the hydrogel matrix plays a decisive role in determining the mechano-responsive luminescent performance of the hydrogels. The response signals in physically doped systems often suffer from low contrast. To address the issue, herein two types of cyano-oligo(p-phenylene vinylene) (cyano-OPV) derivatives, Vin-OPV-Vin and UPy-OPV-Vin, were designed and synthesized as chemically bonded mechanophores. Vin-OPV-Vin contains two polymerizable vinyl groups and serves as a permanent covalent crosslinking point, while UPy-OPV-Vin contains one vinyl group and one ureidopyrimidinone unit, providing covalent anchoring and reversible quadruple hydrogen bonding. In solution, when aggregated, Vin-OPV-Vin readily formed ordered π-π stacked excimer, whereas the bulky UPy group and hydrogen-bonding interactions suppressed compact face-to-face stacking and produced more diverse aggregates. The hydrogel matrix was optimized through orthogonal experiments and prepared by in situ photopolymerization combined with repeated freeze-thaw treatment. By varying the functionality of the mechanophores, chemically crosslinked (Vin-OPV-Vin-PGASMM) and dynamically crosslinked (UPy-OPV-Vin-PGASMM) hydrogels were constructed, respectively. The former exhibited higher fracture stress and Young’s modulus due to permanent covalent crosslinking, while the latter showed better deformation recoveribility because the reversible quadruple hydrogen bonds dissipated energy and allowed chain rearrangement. Upon stretching, both types of hydrogels exhibited MRL properties, and UPy-OPV-Vin-PGASMM showed a higher color contrast, with the CIE coordinates varying from (0.39, 0.59) to (0.33, 0.60) under 0-250% tensile strain. Notably, the dynamically crosslinked system achieved synergistic optimization of mechanoresponsive sensitivity and network adaptability.

Key words: Mechanoresponsive luminescence, hydrogel, mechanochromic mechanophore, chemical crosslinking, dynamic crosslinking