Modulating the Lewis Acidity of Boron Using a Photoswitch

Abstract

Light turns the Lewis acid on: The Lewis acidity of a boron atom integrated into a cyclic dithienylethene photoswitch is modulated by light: 1 a has low Lewis acidity since the p orbital of the boron center is partially occupied by delocalized π electrons, whereas the rearrangement of the π electrons in 1 b reduces the electron density at the boron center and turns the Lewis acid “on”.

Light‐Controllable Ionic Conductivity in a Polymeric Ionic Liquid

“…This decrease in electronic density upon photocyclization is supported by the 13 C NMR where the C2 carbon of the imidazolium shifts from 136.6 ppm to 150.6 ppm (Supporting Information, Figure S3). A similar effect of decreasing the electron density and breaking aromaticity upon photocyclization has been reported by Kawai, Bielawski, and Branda …”

“…Moreover, the photoinduced rearrangement of the π bond in the bridging imidazolium ring can be used to control the electronic properties and chemistry of the imidazolium ring. Photochromic diarylethenes bearing an imidazolium ring have found applications in different areas such as photoswitchable organocatalysts, chemical sensors, and as a new type of Lewis acid . For example, the Bielawski group used a DAE‐based organocatalyst with photoswitchable electron density at the C2 position of the imidazole ring in N ‐heterocyclic carbene adducts to regulate the rate of transesterification reactions .…”

Isomerization and rearrangement of boriranes: from chemical rarities to functional materials

“…In particular, -BMes 2 substitution has proven to be an effective strategy for controlling the color and state-switching of DTEs via the introduction/removal of fluoride ions (F − ), which bind strongly to three-coordinated boron atoms and disrupt the π-conjugation of the molecule [43][44][45]. This approach has also been successfully implemented in the development of diboron- based photoswitches [46] capable of changing between four different states (Fig.…”

Syntheses and Photochromic Studies of Dithienylethene‐Containing Imidazolium Derivatives and Their Reactivity towards Nucleophiles

“…Photochromic dithienylethene‐containing 2‐(2‐pyridyl)imidazoles and their rhenium(I) complexes were reported by Yam and co‐workers in 2007 5. Diarylethene systems based on cationic imidazolium salt6 and electron‐deficient dioxaborole7 were both found to be photoregulated electrophiles. At almost the same time, Yam and co‐workers reported a series of dithienylethene‐containing N , N′ ‐dialkylimidazolium salts, and their metal N ‐heterocyclic carbene (NHC) complexes; the photochromic properties were also studied 8.…”