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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. [ABSTRACT FROM AUTHOR]

Bistable [ c 2] daisy chain rotaxanes with respective extended and contracted forms of [ c 2 ]A and [ c 2 ]B containing a blue-emissive anthracene ( AN ) donor and orange-emissive indandione-carbazole ( IC ) acceptor were successfully synthesized via click reaction. Tunable-emission bistable [ c 2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H 2 O/THF) and FRET (with a compatible energy transfer of E FRET = 33.2%) behaviors after the shuttling process (by adding base), the brightest white-light emission at CIE (0.31, 0.37) with a quantum yield of Φ = 15.64% was obtained in contracted [ c 2 ]B with good control of molecular shuttling to possess higher photoluminescence (PL) quantum yields and better energy transfer efficiencies (i.e., the manipulation of reduced PET and enhanced FRET processes) due to their intramolecular aggregations of blue AN donors and orange IC acceptors with a proper water content of 60% H 2 O. Furthermore, dynamic light-scattering (DLS) and time-resolved photoluminescence (TRPL) measurements, along with theoretical calculations, were utilized to investigate and confirm AIE and FRET phenomena of bistable [ c 2] daisy chain rotaxanes. Especially, both bistable [ c 2] daisy chain rotaxanes [ c 2 ]A and [ c 2 ]B and noninterlocked monomer M could be exploited for the applications of ratiometric fluorescence temperature sensing due to the temperature effects on the AIE and FRET features. Based on these desirable bistable [ c 2] daisy chain rotaxane structures, this work provides a potential strategy for the future applications of tunable multicolor emission and ratiometric fluorescence temperature-sensing materials.