Redox‐Induced Transformation from an Extended to a π‐Stacked Conformer in Acyclic Bis(catecholacetal)s of Acetylacetone

Abstract

Removal of a single electron induced the extended conformers of bis(catecholacetal)s of acetylacetone to instantaneously fold into cyclophane‐like π‐stacked structures (shown schematically).

Electron transfer reactions of rigid, cofacially compressed, π-stacked porphyrin–bridge–quinone systems

“…These -stacked systems have been extensively examined in relation to the degree of intramolecular charge transfer as a function of arene conformation. Likewise, Rathore has extensively examined -stacked polyfluorenes [215,234,235]. In these systems, fluorene rings are held in a cofacial arrangement by a saturated aliphatic backbone.…”

Molecular Actuator: Redox-Controlled Clam-Like Motion in a Bichromophoric Electron Donor

“…to the stabilization of the cationic charge by the effective electronic coupling between the πstacked veratrole moieties (vide infra) and thereby significantly lowering its first oxidation potential when compared to the monochromophoric donor 6 (Eox = 1.22 V) by ∼260 mV. 13 As such, the through-space electronic coupling between the cofacially stacked aryl moieties can also be seen in the electronic spectra of their cation radicals, where characteristic chargeresonance transitions in the near-IR region are observed. 13,14 Accordingly, we generated the cation radicals of 4−6 using stable cation-radical salts [such as CRET +• , Ered = 1.14 V vs SCE and NAP +• , Ered = 1.34 V vs SCE] 15,16 as one-electron aromatic oxidants in dichloromethane as follows.…”

Vertical vs. adiabatic ionization energies in solution and gas-phase: probing ionization-induced reorganization in conformationally-mobile bichromophoric actuators using photoelectron spectroscopy, electrochemistry and theory

“…A detailed investigation of the ionization-induced actuation of V2, V2-locked, Ac2-C2H4 and Ac2-CH2 bichromophores in CH2Cl2 solution has been established in previous studies, [10][11][12] which showed that V2 in solution exists in an open conformation and undergoes ionization-induced folding into a closed conformation on a μs timescale (Fig. 2).…”

“…A series of similar veratrole-and acetal-based actuator molecules (V2, V2-locked, Ac2-C2H4, Ac2-CH2) and model compound V1 were synthesized from previously reported procedures [10][11][12] and were fully characterized by 1 H/ 13 C NMR spectroscopy. Gas-phase photoelectron spectra of all compounds were recorded at the Center for Gas-Phase Electron Spectroscopy at The University of Arizona.…”

“…While the enthalpy gain of a complete cofacial approach of two aromatic systems may reach ∼0.35 V, 7 the overall free energy gain depends significantly on the linker connecting the two chromophores as well as the surrounding environment (i.e., solvent). In this context, an oxidation-induced molecular actuation, [10][11][12] i.e., reversible change in structure, conformation and/or physical properties in response to external stimuli, [13][14][15] represents an ideal case to probe the extent of cationic charge (i.e., hole) stabilization and structural/conformational reorganization in a set of model bichromophoric electron donors.…”