title: A switchable bis-branched [1]rotaxane featuring dual-mode molecular motions and tunable molecular aggregation.
abstract: A multifunctional bis-branched [1]rotaxane containing a perylene bisimide (PBI) core and two identical bistable[1]rotaxane arms terminated with ferrocene units was prepared and characterized by (1)H NMR, (13)C NMR, and 2D ROESY NMR spectroscopies and by HR-ESI spectrometry. The system is shown to possess several key features: (1) In acetone solution, external acid-base stimuli can result in relative mechanical movements of its ring and thread, which can induce extension and contraction movements of the whole system accompanied by a rotational movement of the ferrocene units, thus realizing dual-mode molecular motions, and the optimized conformations at different states are obtained through molecular dynamics simulations employing the general Amber force field. (2) The introduction of PBI enables the system fluorescence encoding through distance-dependent photoinduced electron transfer process from the ferrocene units to the PBI fluorophore. (3) The addition of Zn(2+) can increase the degree of aggregation of the system, while adding base hinders aggregation because of the movement of the macrocycle. The tunable aggregated nanostructural morphologies of [1]rotaxane were examined by scanning electron microscopy. These results can pave the way to achieve precise control of integrated and coupling nanomechanical motions at a single-molecule level and provide more insight into controlling the aggregate behavior of switchable mechanically interlocked molecules.
authors.affiliation: Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology , Shanghai 200237, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Zhan-Qi
authors.initials: ZQ
authors.lastname: Cao
authors.forename: Da-Hui
authors.initials: DH
authors.lastname: Qu
authors.forename: Hans
authors.initials: H
authors.lastname: Ågren
authors.forename: He
authors.initials: H
authors.lastname: Tian
mesh_terms: D039301:Computers, Molecular; D005456:Fluorescent Dyes / Q000737:chemistry; D007094:Imides / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D009038:Motion; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry; D043862:Rotaxanes / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D007094:Imides; D043862:Rotaxanes; C510697:perylene bisimide; D010569:Perylene; D015032:Zinc
keywords: bistable rotaxanes; dual-mode motions; fluorescence; perylene bisimide; tunable aggregation