Expanded Porphyrin-Anion Supramolecular Assemblies: Environmentally Responsive Sensors for Organic Solvents and Anions

Porphyrins
have been used frequently to construct supramolecular
assemblies. In contrast, noncovalent ensembles derived from expanded
porphyrins, larger congeners of naturally occurring tetrapyrrole macrocycles,
are all but unknown. Here we report a series of expanded porphyrin-anion
supramolecular assemblies. These systems display unique environmentally
responsive behavior. Addition of polar organic solvents or common
anions to the ensembles leads to either a visible color change, a
change in the fluorescence emission features, or differences in solubility.
The actual response, which could be followed easily by the naked eye,
was found to depend on the specifics of the assembly, as well as the
choice of analyte. Using the ensembles of this study, it proved possible
to differentiate between common solvents, such as diethyl ether, THF,
ethyl acetate, acetone, alcohol, acetonitrile, DMF, and DMSO, identify
complex solvent systems, as well as distinguish between the fluoride,
chloride, bromide, nitrate, and sulfate anions.