Solvent viscosity-dependent isomerization equilibrium of tetramethoxy-substituted bianthrone

Abstract

The designed and synthesized tetramethoxy-substituted bianthrone exists as an equilibrium mixture of the folded and twisted conformers in solution.

Switching of Redox Properties Triggered by a Thermal Equilibrium between Closed‐Shell Folded and Open‐Shell Twisted Species

“…Normal alkenes have a planar geometry, whereas OCEs are forced to adopt a folded (F) and/or twisted (T) form, the latter of which, in general, has a higher HOMO and a lower LUMO than the former. Due to the large difference in the electronic structure (e.g., the T-form has a smaller HOMO-LUMO gap), their dynamic structural change is accompanied by a change in physical properties, and thus many studies on OCEs have been devoted to developing chromic materials [1][2][3][4] and molecular switches. [5][6][7][8] As exemplified by bianthrone (I) [9,10] and bisthiaxanthylidenes (II), [11,12] which are classified as bistricyclic aromatic enes (BAEs) (Figure 1a), in many cases the F-form is more stable than the corresponding T-form by about 5-20 kcal mol -1 .…”

Biradicaloid Behavior of a Twisted Double Bond

“…20,21 Recently, we demonstrated that the energy gap between the bianthrone conformers can be minimized by methoxy substituents at the 3,3′,6,6′-positions, and we achieved the coexistence of both forms of 2 in equilibrium in solution. 35 We also found that the equilibrium constant depends on the solvent viscosity. On the basis of quantum chemical calculations and a statistical thermodynamic model, we proposed that the central CC bond of the twisted form has torsional elasticity and performs torsional oscillations damped by the solvent viscosity.…”

“…Bianthrone 1 is a well-studied overcrowded ethylene that contains steric repulsion arising from the bulkiness of the tricyclic aromatic rings substituted at both ends (Figure b). − The bianthrones have two structural isomers, a twisted form with a twisted CC bond and a folded form with an untwisted CC bond. The twisted form only exists as a transient species upon heating or light irradiation because the folded form is more energetically stable by about 15 kJ mol –1 . , Therefore, the twisted form has not been isolated and the electronic structure of the twisted CC bond has remained unknown. , …”

Tunable Solid‐State Thermochromism: Alkyl Chain Length‐Dependent Conformational Isomerization of Bianthrones

“…This pronounced contradictory color change was followed by diffuse reflection spectroscopy. The UV‐Vis‐NIR reflection spectra of 2G and 3G showed two bands, one in the visible region (400–500 nm) related to the folded conformer and the other in the near‐IR region (600–1100 nm) related to the twisted conformer (Figure S4) [14a] . The intensity in the near‐IR region was significantly reduced upon heating of 2G , while the intensity in the visible region was reduced upon heating of 3G .…”