Photo- and Thermal Interconversion of Multiconfigurational Strained Hydrocarbons Exhibiting Completely Switchable Oxidation to Stable Dicationic Dyes

Abstract

Highly strained hydrocarbons with two di-/tri-benzocycloheptatriene units were designed as electrochromic overcrowded ethylenes that undergo reversible interconversion with stable dicationic dyes. Due to severe steric repulsion, two configurational isomers (anti,anti-folded and syn,anti-folded forms) were isolated as stable entities. Photo-and thermal interconversion of these isomers proceeded cleanly: one-way photoisomerization occurred from anti,anti-to syn,anti-form and one-way thermal isomerization was observed from syn,anti-to anti,anti-form. Even though both isomers undergo twoelectron oxidation into the same twisted dications, quite different oxidation potentials enable completely selective oxidation of syn,anti-isomers. Thus, the present multi-configurational strained hydrocarbons are capable of switching of activation/deactivation of their electrochromic properties by light/heat.

Flexible C−C Bonds: Reversible Expansion, Contraction, Formation, and Scission of Extremely Elongated Single Bonds

“…Thekey point is the DBCHT unit, which has been used to construct photoresponsive molecules based on overcrowded ethylenes through syn/anti isomerization. [21,22] Another aspect is astructurally fixed cis-stilbene moiety in the DBCHT unit, and thus the intramolecular [2+ +2] cycloaddition reaction could proceed as in DBCHT-dimer to produce ac aged molecule. [23] Thel atter reactivity is more interesting from at opochemical point of view,s ince the solid-state reaction would be applicable for stimuli-responsive systems toward potential applications such as photoswitching,optical recording, and sensing materials.…”

“…The key point is the DBCHT unit, which has been used to construct photoresponsive molecules based on overcrowded ethylenes through syn / anti isomerization [21, 22] . Another aspect is a structurally fixed cis ‐stilbene moiety in the DBCHT unit, and thus the intramolecular [2+2] cycloaddition reaction could proceed as in DBCHT‐dimer to produce a caged molecule [23] .…”

Molecular Recognition by Chalcogen Bond: Selective Charge‐Transfer Crystal Formation of Dimethylnaphthalene with Selenadiazolotetracyanonaphthoquinodimethane

“…The small separation between E1 and E2 in 1 and 2 than in 3 (+0.04, -0.43 V) and 4 (+0.12, -0.38 V) without a fused benzene ring can be explained by the nonplanar structures [20] of 1 and 2. Thus, upon two-electron transfer, a change in geometry [21] from a folded neutral form to a twisted dianionic form (Scheme 3a) is expected, as in other benzo-fused quinodimethane derivatives. The DFT calculation also predicted a curved -skeleton for 1 and 2 (Scheme 3b), which is characterized by the dihedral angles summarized in Table 1.…”

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. Owing 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 and molecular switches . As exemplified by bianthrones I and bisthiaxanthylidenes II , which are classified as bistricyclic aromatic enes (BAEs; Figure a), in many cases the F form is more stable than the corresponding T form by about 5–20 kcal mol −1 .…”