Engineering Control over the Conformation of the Alkyne−Aryl Bond by the Introduction of Cationic Charge
摘要:
A novel arylene-ethynylene molecule has been synthesized. This molecule is more stable in a coplanar form than in a twisted form as in the cases of typical arylene-ethynylene molecules. When the cationic charge was introduced into the pi-conjugated system, the perpendicularly twisted form became more stable than the coplanar state. The conformational change was controlled by introduction and removal of cationic charge, confirmed by the absorption and fluorescence spectroscopy and DFT calculation.
Photo-, Solvent-, and Ion-Controlled Multichromism of Imidazolium-Substituted Diarylethenes
摘要:
AbstractSeeing red: Imidazolium‐substituted diarylethenes show solvent‐ and ion‐controlled chromisms in addition to reversible photochromic reactions. The shift of equilibrium between two closed‐ring isomers with different π‐conjugation length by interaction with nucleophilic species is responsible for the multichromic property (see scheme).magnified imageCationic diarylethenes with an imidazolium ring are synthesized for the first time. The imidazolium cationic moiety is connected directly to the ethene unit as one of the aryl units that take part in the photoinduced pericyclization reaction. The imidazolium‐substituted diarylethenes undergo reversible photochromic reactions in a variety of organic media, including ionic liquids, even though they have a delocalized cationic charge in one of the five‐membered aromatic rings. The closed‐ring isomer shows solvatochromism depending on the solvent donor numbers. Addition of some tetraalkylammonium salts, such as tetrabutyl ammonium nitrate, into the colored organic solution of diarylethene also causes a color change, indicating its ionochromic property. These solvato‐ and ionochromic properties are considered in connection with the shift of chemical equilibrium between the closed‐ring isomers, one with an extended π‐conjugation system and one with limited π‐conjugation due to the strong interaction with solvent molecules and anions with high donor number.