Investigation of Alkyl–Aryl Interactions Using the Azobenzene Switch – The Influence of the Electronic Nature of Aromatic London Dispersion Donors

Abstract

Herein we report the synthesis of non-symmetrically substituted azobenzene derivatives with meta-alkyl substituents on one side and meta-aryl moieties with electron donating or electron withdrawing groups on the other side. The half-lives for the thermal (Z)- to (E)-isomerization of these molecules were measured in n-octane, which allows investigation of the strength of the aryl-alkyl interactions between their substituents. It was found that the London dispersion donor strength of the alkyl substrate is the decisive factor in the observed stabilization, whereas the electronic structure of the aryl fragment does not influence the isomerization in a significant way.

Molecular Wind-Up Meter for the Quantification of London Dispersion Interactions

“…Interestingly, an investigation of aryl substituents at the AB with different electron density revealed that the nature of the aryl group has a marginal effect, while the size of the alkyl group dominates the interactions. 45 Our research group undertook the synthesis of a diverse set of meta-substituted ABs to assess the LD interactions. This comprehensive scope of compounds encompasses linear and bulky alkyl groups as well as para-substituted aryl systems.…”

“…By examining these compounds, we aimed to investigate both alkyl−alkyl and alkyl−aryl interactions in the context of LD interactions (Figure 4). [1][2][3]44,45 Initially, alkyl−alkyl interactions with varying degrees of bulkiness were studied. 1 Temperature-controlled UV−vis spectroscopy was employed for this purpose.…”

“…By examining these compounds, we aimed to investigate both alkyl–alkyl and alkyl–aryl interactions in the context of LD interactions (Figure ). − ,, …”

“…The NCI plots as well as the 2D NOESY NMR experiments suggest significant interactions between alkyl and aryl groups. Interestingly, an investigation of aryl substituents at the AB with different electron density revealed that the nature of the aryl group has a marginal effect, while the size of the alkyl group dominates the interactions …”

“…Our laboratory has established a quantification system based on azobenzenes (ABs), which do not fit the definition of a molecular balance. − ,− AB exists in two different conformers, the ( E )-isomer and the ( Z )-isomer, which can be interconverted by light and heat, respectively (Scheme ). …”