Photoinduced Memory Effect in a Redox Controllable Bistable Mechanical Molecular Switch

Abstract

Mechanically interlocked molecules [1] (MIMs) in the form of multi-and bistable rotaxanes in which the ring component can be switched between different co-conformations in response to external stimuli, constitute an artificial molecular switch. [2] They are of importance when it comes to the development of integrated systems and devices, [3] such as responsive surfaces, [4] molecule-based muscles and actuators, [1d, 5] nanovalves for controlled drug delivery, [6] and molecular electronic devices [7] (MEDs). Although the operation of bistable molecular switches is based on classical switching processes between thermodynamically stable states, it has become clear that the fulfillment of useful functions will only become possible if the rates of the mechanical movement between such states can also be controlled. This approach was used [8] recently to implement ratchet-type mechanisms [9] which are essential ingredients for the construction of molecular motors, [10] and is of considerable relevance for the development of sequential logic devices such as flip-flops and memories.[11] For all these purposes, the ability to be able to adjust the shuttling kinetics [12] by modulating the corresponding energy barriers through external stimuli in a convenient, efficient, and reversible manner [13] is a goal which still poses a considerable challenge to chemists.Herein, we discuss the performance of a molecular switch in the form of a bistable [2]rotaxane (Scheme 1), which 1) undergoes relative mechanical movements of its ring and dumbbell components under redox control and thus can be switched between two states thermodynamically, and wherein 2) the energy barriers between these two states can be controlled kinetically by photochemical means.The design of [2]rotaxane 1 4+ (Scheme 1) is based on a well-studied architecture [7b, 14] in which the ring component is cyclobis(paraquat-p-phenylene) (CBPQT 4+ ) and the dumbbell component is comprised of 1) a tetrathiafulvalene (TTF) Scheme 1. Synthesis of [2]rotaxane trans-1·4 PF 6 and the corresponding dumbbell trans-2.

Photoresponsive Molecular Memory Films Composed of Sequentially Assembled Heterolayers Containing Ruthenium Complexes

“…[33,[46][47][48] Multilayer structures based on Zr IV -phosphonates have been applied for the development of high-k gate dielectrics for low-voltage organic field-effect transistors. [14,26,34,[49][50][51][52][53] In order to build surface-confined molecular devices towards molecular sensora pplications,w eh ave studied redox-active Ru complexest hat bear multipodal phosphonate groups and that have been surface-immobilized on an indium-tin oxide (ITO) electrode. [52] The judiciousd esign of the anchoring ligand in these redox-activec omplexes has allowed us to control the molecular inclusion by redox reactions [54] and to achieve DNA trapping on these immobilized Ru complexes.…”

Single-molecule electronics: from chemical design to functional devices

“…The lifetime of the MSCC can be controlled by isomerization of the TMeAB unit from its trans to cis configuration. Reprinted by permission from John Wiley and Sons, copyright (2012) 391. …”

The eternal youth of azobenzene: new photoactive molecular and supramolecular devices

“…5 [32] . In this species, orthogonal chemical and photochemical stimuli are used to gain full control on the thermodynamics (i.e., the distribution of the rings between the two sites located along the axle) and the kinetics (i.e., the translation rate of the rings between the sites) of molecular shuttling.…”