Chromogenic guest-responsive host compounds which allow rapid guest screening

Abstract

Azo host compounds undergo rapid and clearly visible colour changes from yellow to bright orange/red on complexation with guest molecules, while no colour change is noted in the absence of complexation. This provides a rapid screening method for potential guest compounds as the first step towards the development of guest specific host compounds for use in sensors relying only on a simple, visible colour change readout mechanism.

Guest Signaling Compound: trans-3,3‘-Bis(diphenylhydroxymethyl)azobenzene

“…Recently, Kaftory and co-workers have described a group of bisimidazole derivatives that show solvate-dependent chromogenicity, as well as photochromism, piezochromism, and thermochromism . The latter is associated with loss of the guest from the crystal lattice with concomitant rearrangement and, in this sense, is similar to systems we have described that exhibit crystal-structure-dependent, guest-responsive chromogenicity due to shift in absorption maximum, increased or quenched fluorescence, or color development on irradiation via a mechanism similar to charge-transfer complex formation (photochromism) …”

“…Terminal phenyl groups of nonsolvated 2 form 4-fold phenyl embraces of the type described by Scudder and Dance, as well as participating in π-stacking interactions, Figure a, whereas the predominant concerted aromatic/aromatic interactions in the pyridine solvate include both the aromatic guest and, somewhat unusually in these types of compounds, the aromatic rings of the azobenzene core, Figure b. The dioxane solvate exhibits only weak aromatic/aromatic interactions and is dominated by CH···π interactions between guest and host.…”

Photo-mechanical azobenzene cocrystals and in situ X-ray diffraction monitoring of their optically-induced crystal-to-crystal isomerisation

“…Cocrystallisation has previously been employed to tune solid-state physicochemical properties of molecules, especially for pharmaceutical applications and photochemical synthesis. 24,25 Whereas the formation of azo cocrystals was previously explored through p/p-stacking, 26,27 molecular inclusion, 28,29 hydrogen [30][31][32][33] and halogen bonding, [34][35][36] there have been no reports of photo-mechanical activity in the resulting solids. Moreover, there have not yet been any reports of design or structural characterisation of cocrystals of cis-azobenzenes, most likely due to oen short lifetimes preventing the isolation of single crystals.…”