We report a system in which three distinct dynamic linkages, disulfide (S-S), imine (C=N), and coordinative (N-->metal) bonds were shown to be capable of simultaneous reversible exchange. The "disulfide layer" of the system under study consists of two homo-disulfides, bis(4-aminophenyl) disulfide 1 and bis(4-methoxyphenyl) disulfide 2 that equilibrate in the presence of catalytic amount of triethylamine to favor the formation of a hetero-disulfide product, 4-aminophenyl-4'-methoxyphenyl disulfide 3. The addition of 2-formylpyridine and a metal salt strongly perturbed this 1+2<-->3 equilibrium through the formation of metal complexes incorporating disulfide 1 as a subcomponent. CuI perturbed the equilibrium by a factor of 3.3, and FeII by a factor of 179, in both cases in favor of the homo-disulfides. The disulfide equilibrium could be further modified, following metal-complex formation, by coordinative (transmetallation: substitution of FeII for CuI) or covalent (imine exchange: the substitution of one amine residue for another) exchange. Thus, although the three kinds of dynamic linkages were demonstrated to be mutually compatible, changes at one kind of linkage could be used to predictably perturb an equilibrium involving another.
Isonicotinic acid anthracen-9-ylmethylene-hydrazide (AI), prepared from anthracene-9-carboxaldehyde and isoniazid, exhibited mechano-responsive luminescent emissions; for instance, gentle pressing of the weakly emissive crystals of AI (λ em 527 nm) produced a yellow-green emissive material (λ em 540 nm). Also, the mechano-luminescent emissions of AI could be easily switched "off" upon exposure to N,N-dimethylformamide. Contrastingly, under the same conditions, benzoic acid anthracen-9-ylmethylene-hydrazide (AB) did not exhibit mechano-responsive luminescent emissions. On the basis of UV−vis, fluorescence, Fourier transform infrared spectroscopy, and powder X-ray diffraction (XRD) studies, we suggest that mechano-luminescent emissions of AI were triggered by mechanically induced deformations in the lattice, which affected the intermolecular interactions and aromatic stacking behavior. Again, the mechano-luminescent emissions of AI were switched off when mixed with oxalic acid, although accompanied by a concomitant change in color, from yellow-green to red. Single crystal XRD studies provided vital insights into the interactions of AI with oxalic acid, highlighting the role of hydrogen bonding and anion-mediated aromatic-π interactions.
Three polymorphs of 2-hydroxynaphthaldehyde semicarbazone (2-NOH-S) have been identified, and their mechano-responsive luminescent emissions and interconversions are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.