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

Abstract

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.

Anion Receptor Chemistry

“…Langton et al 32 demonstrated the utility of halogen bonding and its potential superiority to hydrogen bonding in achieving anion binding in water in a series of cyclodextrin-functionalized acyclic (57)(58)(59) and rotaxane (60-62) hosts ( Figure 20). Rotaxane 60, which bound anions via a combination of halogen bonding and hydrogen bonding, displayed a remarkably high affinity of 2,200 M À1 for I À and a selectivity of I À > Br À > Cl À > SO 4 2À in D 2 O.…”

“…A bis(carbazolyl)urea receptor 113 was immobilized onto a gold surface to produce self-assembled monolayers of 113 (113-SAM; Figure 36), which functioned as an extremely sensitive sensor for HP 2 Recently, the use of supramolecular assemblies instead of small-molecule probes has become an increasingly popular approach to creating highly responsive sensory materials. Zhang et al 59 discovered that expanded porphyrins 116 and 117 (Figure 38) formed supramolecular polymers with several diacids (including 4,4 0 -biphenyldisulfonic acid and oxalic acid) in CH 2 Cl 2 , which could be utilized for sensing organic solvents and anions. The polymerization resulted from association between protonated receptors and the anions of the diacids, leading to either 1:1 diprotonated porphyrin-dianion polymer or 1:2 diprotonated porphyrin-monoanion polymers, the latter of which was stabilized by hydrogen bonding between the remaining protonated carboxylic acid groups.…”

Selective Nitrate Recognition by a Halogen‐Bonding Four‐Station [3]Rotaxane Molecular Shuttle

“…To date only a relatively small number of nitrate‐selective tripodal acyclic, macrocyclic and cage‐like host systems have been reported that utilise convergent hydrogen bonding (HB) and/or anion–π interactions to recognise the oxoanion in polar organic solvents 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19…”

Selective Nitrate Recognition by a Halogen‐Bonding Four‐Station [3]Rotaxane Molecular Shuttle

“…[6] To date only arelatively small number of nitrateselective tripodal acyclic,m acrocyclic and cage-like host systems have been reported that utilise convergent hydrogen bonding (HB) and/or anion-p interactions to recognise the oxoanion in polar organic solvents. [7][8][9][10][11][12][13][14][15][16][17][18][19] Thec hallenge of developing synthetic receptors that can rival the anion recognition properties of biotic systems relies upon the arrangement of at hree-dimensional convergent array of numerous HB donor groups in an optimized geometry for recognition of the complementary guest. [20,21] To meet this challenge we have exploited anion-templation to construct interlocked host structures [22,23] whose unique threedimensional cavities encapsulate anionic guest species.…”