: We present an efficient strategy for on-surface engineering of organic metal-free supramolecular complexes with long-term spin protection. By vacuum deposition of azafullerene (C59N•) monomers on a pre-deposited template layer of [10]cycloparaphenylene ([10]CPP) nanohoops on Au(111) surface we exploit the molecular shape matching between the C59N• and [10]CPP for the azafullerene encapsulation with nanohoops in a guest-host complexation geometry. C59N•⊂[10]CPP supramolecular complexes self-assemble into an extended two-dimensional hexagonal lattice yielding a high density network of stable spin-1/2 radicals. We find compelling evidence for electronic coupling between the guest C59N• and the host [10]CPP in supramolecular species. At the same time, [10]CPP effectively protects the radical state of encapsulated azafullerenes against dimerization and inhibits C59N• coupling to the Au substrate. Azafullerene encapsulation by nanohoops represents a viable realization of molecular spin protection while simultaneously demonstrating exceptional self-assembling properties by which large-scale 2D architectures of molecular spins can be realized.
