Two-dimensional conjugated polymers with weakened interlayer interaction for highly sensitive visible responsiveness to compression stresses

Abstract

Detection of mechanical stresses requires microscopic molecular motion triggered by macroscopically applied force. Polydiacetylene (PDA), a stimuli-responsive color-changing material, generally has no responsiveness to compression stresses. We found that a layered PDA with weakened interlayer interactions exhibits direct visible color changes in response to compression stresses. An amphiphilic diacetylene (DA) monomer, 1-(10,12-pentacosadiynyl) pyridinium bromide (PCPy⁺Br⁻), formed a lamellar structure with weakened interlayer and intermolecular interactions originating from the bulky cations and anions in the interlayer space. The resultant PDA exhibited blue-to-red color changes in response to compression stresses (P) in the range of 2.5–125 MPa. In previous works, visible detection of P < 50 MPa without excitation light has not been achieved using only mechanoresponsive materials. Moreover, the compression-stress distribution was visualized using the PDA-coated paper substrate.