Tu Thi Kim Cuc, a Yun-Chen Tso, a Ting-Chi Wu, a Pham Quoc Nhien, b Trang Manh Khang, a Bui Thi Buu Hue, b Wei-Tsung Chuang c and Hong-Cheu Lin * ad
a Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 300093, Taiwan
E-mail: linhc@nycu.edu.tw
b Department of Chemistry, College of Natural Sciences, Can Tho University, Can Tho City 94000, Vietnam
c National Synchrotron Radiation Research Center, Hsinchu 300092, Taiwan
d Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu 300093, Taiwan
The first integration of dual slide-ring motion of [c2] daisy chain molecules (as backbones) and α-cyclodextrin (α-CD)-based polyrotaxanes (as cross-linkers) into mechanofluorophoric polyurethane (PU) frameworks was successfully proceeded through step-growth polymerization to yield PU films with distinctive mechanical and optical properties under stress. The intrinsic elastic and stretchable capabilities of the PU films consisting of both mechanically interlocked molecules (MIMs) via the molecular design of daisy chain backbones and polyrotaxane cross-linkers with long gliding movements were evidently enhanced, where the contributions of both extended/contracted forms in daisy chains and different α-CD numbers in polyrotaxane cross-linkers were also investigated. Moreover, reversible ratiometric fluorescence and energy transfer features between green-emitting naphthalimide donors and yellow-orange-emitting mechanofluorophoric rhodamine acceptors could be attained during stretching and relaxation processes. In addition, the stretching deformation of PU films was studied using X-ray diffraction (XRD) techniques for confirming the correlated morphological properties of stretching states in the oriented PU films. Appealingly, notable shape recovery and reversible ratiometric mechanofluorescence behavior of PU films could be achieved upon heating, signifying the potential of PU films with artificial molecular muscle functions of daisy chains accompanied by pulley effects of polyrotaxane cross-linkers, offering excellent mechanical and optical characteristics for various applications in advanced functional materials.