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Herein, we report a series of azobenzene-substituted triptycenes. In their design, these switching units were placed in close proximity, but electronically separated by a sp 3 center. The azobenzene switches were prepared by Baeyer-Mills coupling as key step. The isomerization behavior was investigated by 1 H NMR spectroscopy, UV/Vis spectroscopy, and HPLC. It was shown that all azobenzene moieties are efficiently switchable. Despite the geometric decoupling of the chromophores, computational studies revealed excitonic coupling effects between the individual azobenzene units depending on the connectivity pattern due to the different transition dipole moments of the π→π* excitations. Transition probabilities for those excitations are slightly altered, which is also revealed in their absorption spectra. These insights provide new design parameters for combining multiple photoswitches in one molecule, which have high potential as energy or information storage systems, or, among others, in molecular machines and supramolecular chemistry., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Predictive models based on incremental systems exist for many chemical phenomena, thus allowing easy estimates. Despite their low magnitude in isolated systems London dispersion interactions are ubiquitous in manifold situations ranging from solvation to catalysis or in biological systems. Based on our azobenzene system, we systematically determined the London dispersion donor strength of the alkyl substituents Me, Et, iPr up to tBu. Based on this data, we were able to implement an incremental system for London dispersion for the azobenzene scheme. We propose an equation that allows the prediction of the effect of change of substituents on London dispersion interactions in azobenzenes, which has to be validated in similar molecular arrangements in the future., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Azobenzenes are widely utilized as molecular photoswitches for control of nanoscale processes. Their photoisomerization reaction is highly robust and is retained even in extremely rigid systems. Currently, it is not clear what geometric restrictions are required to block this isomerization successfully. We present here a combined experimental and theoretical study on the ultrafast dynamics of cyclotrisazobenzene (CTA) and demonstrate that the structural constraints in CTA prevent isomerization of the photoswitch units. In the developed molecular picture, the N=N bonds respond elastically to the motion along the isomerization coordinates, which leads to ultrafast and complete dissipation of the UV excitation as heat. Based on this property, CTA and possibly other similarly designed molecules can be utilized as UV absorbers, for example in sunscreens; other potential applications are also envisioned., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Photoswitchable ligands are powerful tools to control biological processes at high spatial and temporal resolution. Unfortunately, such ligands exist only for a limited number of proteins and their development by rational design is not trivial. We have developed an in vitro evolution strategy to generate light-activatable peptide ligands to targets of choice. In brief, random peptides were encoded by phage display, chemically cyclized with an azobenzene linker, exposed to UV light to switch the azobenzene into cis conformation, and panned against the model target streptavidin. Isolated peptides shared strong consensus sequences, indicating target-specific binding. Several peptides bound with high affinity when cyclized with the azobenzene linker, and their affinity could be modulated by UV light. The presented method is robust and can be applied for the in vitro evolution of photoswitchable ligands to virtually any target.

Two bands make light work: since the isomerization of azobenzenes is usually induced by UV light, its application is limited in living systems. A new azobenzene switch now operates entirely in the visible range. The new design is based on the introduction of OMe groups in the ortho positions, which splits the n-π* transition into two absorption bands. The two isomeric forms can be obtained with more than 80 % enrichment from the respective photostationary state., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Azobenzenes have attracted great interest in recent years because of their ability to change conformation upon irradiation. This property has been featured in several applications not only in organic chemistry but also in biology. Even though monoazobenzenes have been extensively studied and documented in the literature, only a few methods are available for the synthesis of oligo-ortho-azobenzenes. Also, their photochemical properties have not been reported so far. This study shows an efficient strategy for the preparation of oligo-ortho-azobenzenes and the investigation of their photochemical properties. It is demonstrated that the absorption spectra are highly influenced by the substituents. Interestingly, none of the ortho-bis-, tris-, or tetra-azobenzenes showed any E → Z isomerization. Only the ortho-nitrogen-substituted monoazobenzenes' photochromic behavior upon UV irradiation was observed., (© 2011 American Chemical Society)

Azobenzenes (ABs) are versatile compounds featured in numerous applications for energy storage systems, such as solar thermal storages or phase change materials. Additionally, the reversible one‐electron reduction of these diazenes to the nitrogen‐based radical anion has been used in battery applications. Although the oxidation of ABs is normally irreversible, 4,4'‐diamino substitution allows a reversible 2e− oxidation, which is attributed to the formation of a stable bis‐quinoidal structure. Herein, we present a system that shows a bipolar redox behaviour. In this way, ABs can serve not only as anolytes, but also as catholytes. The resulting redox potentials can be tailored by suitable amine‐ and ring‐substitution. For the first time, the solid‐state structure of the oxidized form could be characterized by X‐ray diffraction. [ABSTRACT FROM AUTHOR]

Herein, we report a series of azobenzene‐substituted triptycenes. In their design, these switching units were placed in close proximity, but electronically separated by a sp3 center. The azobenzene switches were prepared by Baeyer–Mills coupling as key step. The isomerization behavior was investigated by 1H NMR spectroscopy, UV/Vis spectroscopy, and HPLC. It was shown that all azobenzene moieties are efficiently switchable. Despite the geometric decoupling of the chromophores, computational studies revealed excitonic coupling effects between the individual azobenzene units depending on the connectivity pattern due to the different transition dipole moments of the π→π* excitations. Transition probabilities for those excitations are slightly altered, which is also revealed in their absorption spectra. These insights provide new design parameters for combining multiple photoswitches in one molecule, which have high potential as energy or information storage systems, or, among others, in molecular machines and supramolecular chemistry. [ABSTRACT FROM AUTHOR]

By combination of two photochromic molecules as multistate photoswitches new properties regarding to molecular solar thermal (MOST) energy storage systems and information storage capacity of smart materials are expected. By fusing the azobenzene with the norbornadiene system, new multinary photoswitches were designed. A successful synthesis towards different analogues was developed via Suzuki coupling reaction as key step. The isomerization behaviour of these norbornadiene‐azobenzene fusions was studied by UV‐Vis and 1H NMR spectroscopy in different solvents investigating the electronic communication within these multinary‐photochromic systems. [ABSTRACT FROM AUTHOR]

Large substituents are commonly seen as entirely repulsive through steric hindrance. Such groups have additional attractive effects arising from weak London dispersion forces between the neutral atoms. Steric interactions are recognized to have a strong influence on isomerization processes, such as in azobenzene-based molecular switches. Textbooks indicate that steric hindrance destabilizes the Z isomers. Herein, we demonstrate that increasing the bulkiness of electronically equal substituents in the meta-position decreases the thermal reaction rates from the Z to the E isomers. DFT computations revealed that attractive dispersion forces essentially lower the energy of the Z isomers. [ABSTRACT FROM AUTHOR]

Azo compounds, computational chemistry, excitonic coupling, isomerization, photochemistry Keywords: azo compounds; computational chemistry; excitonic coupling; isomerization; photochemistry EN azo compounds computational chemistry excitonic coupling isomerization photochemistry 1 1 1 07/08/22 20220706 NES 220706 B You can't separate this couple b : One of the azo-substituted tripycenes synthesized in this work is highlighted in front of its UV-Vis absorption spectrum. Cover Feature: Azobenzene-Substituted Triptycenes: Understanding the Exciton Coupling of Molecular Switches in Close Proximity (Chem. Eur. J. 38/2022). [Extracted from the article]