A Visible‐Light‐Triggered Conformational Diastereomer Photoswitch in a Bridged Azobenzene

Abstract

Ketal-substituted bridged azobenzenes have been synthesized; these display a symmetrical boat conformation with the ketal in pseudo-equatorial positions. These bridged Z-azobenzenes (Z1 ) readily photoisomerize to the E-isomer as well as another Z-conformer (Z2 ) with ketal function on the pseudo-axial position upon irradiation at 406 nm. The two diastereomeric conformers display distinct physicochemical characteristics. Spectroscopic and NMR investigations supported that interconversion of two conformers occurs via the E-isomer, with good photochemical quantum yield (ΦZ1→E =0.45±0.03, ΦE→Z1 =0.33±0.05, ΦE→Z2 =0.37±0.06 and ΦZ2→E =0.36±0.04). The system shows high photostability and no thermal equilibrium between the two stable Z1 and Z2 conformers.

Kinetic study of azobenzene E/Z isomerization using ion mobility-mass spectrometry and liquid chromatography-UV detection

“…Note also that due to silver complexation, the central CNNC moiety within Z2_Ag1 is slightly more distorted (2.6°) as compared to the neutral crystal structure (0.6°). 17 The effect is much less pronounced for Z1_Ag4, the CNNC moiety being planar (0.02°). NNC angles are smaller for (118.5-118.6°)…”

“…16 The synthesis and isomerization properties of ketal-substituted bridged azobenzenes, presenting a highly twisted unstable E isomer has recently been reported. 17 A particularity of this system is the existence of two stable Z diastereoisomers namely Z1 and Z2 (Scheme 1), whose relative proportions can be varied depending on the irradiation wavelength. 17 This uncommon threecomponent switching system proved especially challenging to analyze by UV-VIS absorption spectroscopy, because no characteristic wavelength allows the quantitation for E→Z thermal back relaxation process.…”

“…Thermal-and photo-induced isomerization pathways of the bridged azobenzene derivative presently studied. 17 hν corresponds to irradiation with UV or visible light, and Δ to heating.…”

Reversible light-driven magnetic switching of salen cobalt complex

“…Powder samples of o-1-Co(II) undergo abrupt, complete and hysteretic SCO, which is possibly due to the crystallographic phase change and the associated intermolecular interaction change [38,39]. o-1-Co (II) possesses photoactive anti-parallel (ap-) configuration and photoinactive parallel (p-) configuration [40][41][42][43][44][45][46][47]. Due to the typical rapid rotation of flexible aryl groups, the two conformers present anti-parallel:parallel with ratio of 3:2 in this system, thus resulting in difficulty of structured inter- Meanwhile, we cannot exclude the influence of crystallized water molecules and counter ions on the SCO properties.…”

Water-Soluble Colorimetric Amino[bis(ethanesulfonate)] Azobenzene pH Indicators: A UV–Vis Absorption, DFT, and 1H–15N NMR Spectroscopy Study

“…1,2 Their relative ease of synthesis and photocontrollable cis/trans isomerization 3,4 make them useful components in smart materials, 5,6 metal–organic frameworks (MOFs), 7,8 self-assembled monolayers, 9,10 nonlinear optical materials, 11 and supramolecular devices. 12−16 Azobenzenes are also a classic scaffold for pH indicators and metal ion chemosensors. 17−24 In fact, the chromophore represents the largest percentage of commercially available pH indicators.…”