The Quest for Molecular Grippers: Photo‐Electric Control of Molecular Gripping Machinery

Abstract

The quest for nanoscale molecular machines has inspired the search for their close relatives, molecular grippers. This path was paved by the development of resorcin[4]arene cavitands and their quinone‐based redox‐active congeners. In this Concept article, the efforts to design and establish the control of quinone‐functionalized resorcin[4]arenes by electronic and electromagnetic stimuli is described. This was achieved by relying on paramagnetic semiquinone radical anions formed electrochemically or by photoredox catalysis. The gripper‐like motion of such species could not be studied by conventional NMR spectroscopy. Instead, an entirely different approach had to be developed that included various electroanalytical and spectroelectrochemical methods, including UV/Vis/NIR spectroelectrochemistry, pulsed EPR and Davies 1H ENDOR spectroscopy, transient absorption spectroscopy, and time‐resolved luminescence measurements, besides density functional theory calculations and X‐ray crystallography. The conceptual breakthroughs are reviewed as well as the current state and future perspectives of photoredox‐switchable molecular grippers.

Smart Polymers for Advanced Applications: A Mechanical Perspective Review

“…The so-called mechanophores, i.e., mechanically sensitive chemical groups built into the chemical structure of the polymer, are considered first; they usually have photochromic properties, since on mechanical stress the chemical structure of the molecule changes and so a different color light is emitted (Brown and Craig, 2015). However, other kinds of groups exist whose mechanical sensibility manifests through a geometric conformational change (Milić and Diederich, 2019).…”

“…The transition between the two stable conformation states triggered by environmental stimuli (such as temperature, light, electric and/or magnetic fields, chemical agents, mechanical stress, biological agents, etc.) enables the development of molecular-level actuators and materials, regardless of the dimensional requirement of the application (Randolph et al, 2012;Kocak et al, 2017;Milić and Diederich, 2019). Such state of materials are ubiquitous in biology, such as in immunoglobulin (Prigogine and Nicolis, 1971), where the unfolding of molecular segments is triggered by mechanical actions (Marszalek et al, 1999).…”

Mechanically‐Driven Vase–Kite Conformational Switch in Cavitand Cross‐Linked Polyurethanes

“…Much effort has been devoted to the development of molecular architectures capable to perform mechanical‐like movements (output) as a consequence of external stimuli (input) . Among the variety of switches that mimic different macroscopic objects, molecular grippers stand out for the uptake/release of molecular objects . To act as a gripper, a molecule should close and open upon external stimulation to grab and release molecular objects.…”

“…The energy barrier for a single flap interconversion has been estimated in 7.6 kcal mol −1 by DFT calculations . The vase‐kite interconversion has been extensively investigated in solution via different stimuli, such as pH, temperature, Zn 2+ coordination and redox …”

Stimuli‐Responsive Resorcin[4]arene Cavitands: Toward Visible‐Light‐Activated Molecular Grippers

“…Stimuli‐responsive molecules, such as molecular machines and switches, are molecules that upon stimulation can move their submolecular components in a defined manner to produce a specific function. Molecular grippers are a type of switch that upon stimuli activation can encapsulate or release smaller molecules . Such a feature is highly desired for the development of next‐generation sensors, receptors, energy conversion devices, and catalysts.…”