The Green Box: An Electronically Versatile Perylene Diimide Macrocyclic Host for Fullerenes.

The powerful electron accepting ability of fullerenes makes them ubiquitous components in biomimetic donor-acceptor systems that model the intermolecular electron transfer processes of Nature's photosynthetic center. Exploiting perylene diimides (PDIs) as components in cyclic host systems for the noncovalent recognition of fullerenes is unprecedented, in part because archetypal PDIs are also electron deficient, making dyad assembly formation electronically unfavorable. To address this, we report the strategic design and synthesis of a novel large, macrocyclic receptor composed of two covalently strapped electron-rich bis-pyrrolidine PDI panels, nicknamed the "Green Box" due to its color. Through the principle of electronic complementarity, the Green Box exhibits strong recognition of pristine fullerenes (C60/70), with the noncovalent ground and excited state interactions that occur upon fullerene guest encapsulation characterized by a range of techniques including electronic absorption, fluorescence emission, NMR and time-resolved EPR spectroscopies, cyclic voltammetry, mass spectrometry, and DFT calculations. While relatively low polarity solvents result in partial charge transfer in the host donor-guest acceptor complex, increasing the polarity of the solvent medium facilitates rare, thermally allowed full electron transfer from the Green Box to fullerene in the ground state. The ensuing charge separated radical ion paired complex is spectroscopically characterized, with thermodynamic reversibility and kinetic stability also demonstrated. Importantly, the Green Box represents a seminal type of C60/70 host where electron-rich PDI motifs are utilized as recognition motifs for fullerenes, facilitating novel intermolecular, solvent tunable ground state electronic communication with these guests. The ability to switch between extremes of the charge transfer energy continuum is without precedent in synthetic fullerene-based dyads.

Contrasting anion recognition behaviour exhibited by halogen and hydrogen bonding rotaxane hosts.

A rotaxane host system containing a novel halogen bonding (XB) 5-iodo-1,2,3-triazole functionalised pyridinium motif, within its axle component, has been prepared via a ring closing metathesis reaction, using chloride as a template. Proton NMR titration experiments, in competitive 1 : 1 CDCl3-CD3OD solvent media, showed the XB rotaxane selectively bound halides over larger, more basic oxoanions. An all hydrogen bonding proto-triazole containing rotaxane analogue was also prepared, which in stark contrast demonstrated a reversal in the anion selectivity trend, with a preference for dihydrogen phosphate over the halides which is unprecedented for an interlocked host system.

Synthesis and EPR studies of the first water-soluble N@C60 derivative.

The first water-soluble derivative of the paramagnetic endohedral fullerene N@C60 has been prepared through the covalent attachment of a single addend containing two permethylated ß-cyclodextrin units to the surface of the carbon cage. The line width of the derivative's EPR signal is highly sensitive to both the nature of the solvent and the presence of Cu(ii) ions in solution.

Selective perrhenate recognition in pure water by halogen bonding and hydrogen bonding alpha-cyclodextrin based receptors.

Alpha-cyclodextrin based anion receptors functionalised with pendant arms containing halogen and hydrogen bond donor motifs display selective association of perrhenate in aqueous media at neutral pH. NMR and ITC anion binding investigations reveal the halogen bonding receptor to be the superior host.