Multi-mode-driven molecular shuttles : photochemically and chemically reactive benzoxazole-containing rotaxanes

• Main Author: Sun, Weiquan
• Published: University of Edinburgh 2008
• Subjects: 547.05
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662606

Chapter Two describes the use of intercomponent interactions between the benzoxazole-containing motif in the thread and the benzylic amide macrocycle which provides an accessible and efficient method for the synthesis of a model <i>E</i>-[2]rotaxane. Irradiation of this <i>E</i>-isomer produces the corresponding <i>Z</i>-[2]rotaxane, in which the maximum number of intercomponent hydrogen bonds changes from four (<i>E</i>) to two (<i>Z</i>), considerably reducing the binding strength between the thread and the macrocycle. Lying in the macrocycle discrimination between the ‘matched’ (<i>E</i>) and ‘mismatched’ (<i>Z</i>) binding sites, two reversible light-driven molecular shuttles have been generated. Both shuttles exhibit remarkable positional integrity of the macrocycle on the thread before and after the photo stimulus. The synthesis of a hydrogen-bonded benzimidazole-motif-templated [2]rotaxane with excellent yield is reported in Chapter Three. Upon UV irradiation of this <i>E</i>-[2]rotaxane, none of the corresponding <i>Z</i>-isomer is produced and its heavily suppressed photoisomerisation reveals some effects of hydrogen-bonding and/or mechanical interlocking on the benzimidazole-containing binding site. Chapter Four describes how a chemically driven molecular machine has been designed, based on a switchable [2]rotaxane with two different recognition sites. Switching can occur using either the adjustment of pH or addition of zinc ions. This molecular shuttle can switch the macrocycle between two distinct translational forms with high positional integrity and relatively fast dynamics. The study of such a simple process is useful for the future design of molecular devices that mimick the actions of extremely complex bio-motor molecules. Furthermore, the proton- or Zn²⁺-induced large amplitude motion in this bistable molecular shuttle implies that it can act as a potential probe to detect protons or zinc ions. Chapter Five describes the first synthesis and characterisation of a [2]rotaxane containing an octanuclear heterometallic {Cr₇Ni] wheel. As {Cr₇Ni} is an antiferromagnetically coupled wheel with a nondiamagnetic ground state (<i>S</i> = ½), this methodology will make it possible to examine such fascinating magnetic properties within interlocked structures for the first time.