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Fluorescent dye based nanoparticles (NPs) have received increased interest due to their high brightness and stability. In fluorescence microscopy and assays, high signal to background ratios and multiple channels of...

 

Subcomponent self-assembly relies on cation coordination whereas the roles of anions often only emerge during the assembly process. When sites for anions are instead pre-programmed, they have the potential to be used as orthogonal elements to build up structure in a predictable and modular way. We explore this idea by combining cation (M + ) and anion (X − ) binding sites together and show the orthogonal and modular build up of structure in a multi-ion assembly. Cation binding is based on a ligand (L) made by subcomponent metal-imine chemistry (M + = Cu + , Au + ) while the site for anion binding (X − = BF 4 − , ClO 4 − ) derives from the inner cavity of cyanostar (CS) macrocycles. The two sites are connected by imine condensation between a pyridyl-aldehyde and an aniline-modified cyanostar. The target assembly [LM-CS-X-CS-ML], + generates two terminal metal complexation sites (LM and ML) with one central anion-bridging site (X) defined by cyanostar dimerization. We showcase modular assembly by isolating intermediates when the primary structure-directing ions are paired with weakly coordinating counter ions. Cation-directed (Cu + ) or anion-bridged (BF 4 − ) intermediates can be isolated along either cation–anion or anion–cation pathways. Different products can also be prepared in a modular way using Au + and ClO 4 − . This is also the first use of gold( i ) in subcomponent self-assembly. Pre-programmed cation and anion binding sites combine with judicious selection of spectator ions to provide modular noncovalent syntheses of multi-component architectures. 

Dipolar interactions are ever‐present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge‐to‐edge tiling and face‐to‐face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge‐to‐edge contacts to reorder the stability of two surface‐bound 2D polymorphs. The impact on dipole‐enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short‐range (3.4 Å)anti‐parallel dipole contacts. Despite this situation, the reduction in self‐association was attributed to long‐range (~6.4 Å) dipolar repulsions between π‐stacked macrocycles. This work highlights our ability to control the build‐up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self‐assembly.

 

A bistable [2]pseudorotaxane 1⊂CBPQT·4PF 6 and a bistable [2]rotaxane 2·4PF 6 have been synthesised to measure the height of an electrostatic barrier produced by double molecular oxidation (0 to +2). Both systems have monopyrrolotetrathiafulvalene (MPTTF) and oxyphenylene (OP) as stations for cyclobis(paraquat- p -phenylene) (CBPQT 4+ ). They have a large stopper at one end while the second stopper in 2 4+ is composed of a thioethyl (SEt) group and a thiodiethyleneglycol (TDEG) substituent, whereas in 1⊂CBPQT 4+ , the SEt group has been replaced with a less bulky thiomethyl (SMe) group. This seemingly small difference in the substituents on the MPTTF unit leads to profound changes when comparing the physical properties of the two systems allowing for the first measurement of the deslipping of the CBPQT 4+ ring over an MPTTF 2+ unit in the [2]pseudorotaxane. Cyclic voltammetry and 1 H NMR spectroscopy were used to investigate the switching mechanism for 1⊂CBPQT·MPTTF 4+ and 2·MPTTF 4+ , and it was found that CBPQT 4+ moves first to the OP station producing 1⊂CBPQT·OP 6+ and 2·OP 6+ , respectively, upon oxidation of the MPTTF unit. The kinetics of the complexation/decomplexation process occurring in 1⊂CBPQT·MPTTF 4+ and in 1⊂CBPQT·OP 6+ were studied, allowing the free energy of the transition state when CBPQT 4+ moves across a neutral MPTTF unit (17.0 kcal mol −1 ) or a di-oxidised MPTTF 2+ unit (24.0 kcal mol −1 ) to be determined. These results demonstrate that oxidation of the MPTTF unit to MPTTF 2+ increases the energy barrier that the CBPQT 4+ ring must overcome for decomplexation to occur by 7.0 kcal mol −1 . 

The prevalence of anion‐cation contacts in biomolecular recognition under aqueous conditions suggests that ionic interactions should dominate the binding of anions in solvents across both high and low polarities. Investigations of this idea using titrations in low polarity solvents are impaired by interferences from ion pairing that prevent a clear picture of binding. To address this limitation and test the impact of ion‐ion interactions across multiple solvents, we quantified chloride binding to a cationic receptor after accounting for ion pairing. In these studies, we created a chelate receptor using aryl‐triazole CH donors and a quinolinium unit that directs its cationic methyl inside the binding pocket. In low‐polarity dichloromethane, the 1 : 1 complex (logK_1 : 1~ 7.3) is more stable than neutral chelates, but fortuitously comparable to a preorganized macrocycle (logK_1 : 1~ 6.9). Polar acetonitrile and DMSO diminish stabilities of the charged receptor (logK_1 : 1~ 3.7 and 1.9) but surprisingly 100‐fold more than the macrocycle. While both receptors lose stability by dielectric screening of electrostatic stability, the cationic receptor also pays additional costs of organization. Thus even though the charged receptor has stronger binding in apolar solvents, the uncharged receptor has more anion affinity in polar solvents.