Hybrid Photoactive Assemblies:  Electron Injection from Host−Guest Complexes into Semiconductor Nanoparticles

Novel ternary assemblies consisting of fully encapsulated host−guest complexes (hemicarceplexes) and wide band gap semiconductor nanoparticles were investigated. The water-soluble amphiphilic host (octacarboxyhemicarcerand) traps the hydrophobic chromophore within its cavity and binds to the surface of metal oxide nanoparticles. Fluorescence quenching and fast charge injection, k forward ≥ 7 × 109 s-1, from the S2 state of encapsulated azulene were observed. Charge recombination proceeds at a much lower rate of 2 × 107 s-1. Interestingly, the recombination kinetics is homogeneous, suggesting that electron tunneling through the wall of the “molecular container” is the rate-limiting step of the process.