Thioether‐Functionalized Quinone‐Based Resorcin[4]arene Cavitands: Electroswitchable Molecular Actuators

Abstract

The utility of molecular actuators in nanoelectronics requires activation of mechanical motion by electric charge at the interface with conductive surfaces. We functionalized redox‐active resorcin[4]arene‐quinone cavitands with thioethers as surface‐anchoring groups at the lower rim and investigated their propensity to act as electroswitchable actuators that can adopt two different conformations in response to changes in applied potential. Molecular design was assessed by DFT calculations and X‐ray analysis. Electronic properties were experimentally studied in solution and thin films electrochemically, as well as by X‐ray photoelectron spectroscopy on gold substrates. The redox interconversion between the oxidized (quinone, Q) and the reduced (semiquinone, SQ) state was monitored by UV‐Vis‐NIR spectroelectrochemistry and EPR spectroscopy. Reduction to the SQ state induces a conformational change, providing the basis for potential voltage‐controlled molecular actuating devices.

Vase‐Kite Equilibrium of Resorcin[4]arene Cavitands Investigated Using Molecular Dynamics Simulations with Ball‐and‐Stick Local Elevation Umbrella Sampling

“…[62] Finally, in EPR, the distance between flaps involving functional groups presenting unpaired electrons can be characterized. [57][58][59][60] Based on these experiments, the VASE-KITE interconversion of various resorcin [4]arenes in different solvents was found to take place on a time scale of about 0.1 -1 ms at room temperature. [34] The KITE1 and KITE2 conformations interconvert on a time scale that is shorter by about an order of magnitude.…”

Spectro-electrochemical toolbox for monitoring and controlling quinone-mediated redox-driven molecular gripping

“…The experimental details are based on previously reported procedures [9][10][11][12][30][31][32][33][34][35][36][37].…”

“…For instance, Echegoyen and co-workers explored the multiple redox states of calix [4]quinones by using cyclic and rotating disc voltammetry, illustrating the possibility to control their properties in response to the electric charge [22][23][24]. Whereas the flexibility of calixquinones prevented their utility in bistable gripper-like switching, the corresponding electrochemical analytical approach was directly applicable to quinone-based resorcin [4]arenes, which were proven ideal platforms for developing molecular gripper analogues [4,[10][11][12]15,16,31].…”

Redox‐Responsive Macrocyclic Hosts Based on Calix[4]arene and Calix[4]resorcinarene Scaffolds

“…Attachment of the thioester groups to the switching diquinone cavitands allowed their electrochemical investigation in monolayers on gold surfaces. [176] Increasing the scope of available switching stimuli, the photoredox-controlable molecular grippers were reported in 2018. [177] The vase-kite switching process is induced by the intermolecular transfer of the photochemically generated electron from a dissolved photoreductant, [Ru(bpy) 3 ] 2 + , to the two quinone walls of the cavitand generating the bis-SQ cavitand intermediate, in the presence of a sacrificial electron donor to regenerate the photoreductant.…”