Controllable Aggregation-Induced Emission and Förster Resonance Energy Transfer Behaviors of Bistable [2] Daisy Chain Rotaxanes for White-Light Emission and Temperature-Sensing Applications.

Bistable [2] daisy chain rotaxanes with respective extended and contracted forms of 2 and 2 containing a blue-emissive anthracene () donor and orange-emissive indandione-carbazole () acceptor were successfully synthesized via click reaction. Tunable-emission bistable [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 HO/THF) and FRET (with a compatible energy transfer of = 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 2 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 donors and orange acceptors with a proper water content of 60% HO. 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 [2] daisy chain rotaxanes. Especially, both bistable [2] daisy chain rotaxanes 2 and 2 and noninterlocked monomer 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 [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.