The Green Box: An Electronically Versatile Perylene Diimide Macrocyclic Host for Fullerenes [component]

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 centre. 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 unfavourable. To address this, we
more » ... t the strategic design and synthesis of a novel large, macrocyclic receptor comprised of two covalently strapped electron-rich bis-pyrrolidine PDI panels, nicknamed the "Green Box" due to its colour. Through the principle of electronic complementarity, the Green Box exhibits strong recognition of pristine fullerenes (C60/70), with the non-covalent ground and excited state interactions that occur upon fullerene guest encapsulation characterised by a range of techniques including electronic absorption, fluorescence emission, NMR and time-resolved EPR spectroscopies, cyclic voltammetry and mass spectrometry. Whilst 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 Green Box to fullerene in the ground state. Both species in the ensuing charge separated radical ion paired complex are spectroscopically characterised, with thermodynamic reversibility and significant kinetic stability also demonstrated. Importantly, the Green Box represents a seminal type of C60/70 host where electron-rich PDI motifs are utilised as recognition motifs for fullerenes, facilitating novel intermolecular, solvent tuneable 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.
doi:10.1021/jacs.9b10929.s002 fatcat:ktrpvwhghzhpjhwid5oft5mzre