Enhancement of Energy Utilization in Light-Harvesting Dendrimers by the Pseudorotaxane Formation at Periphery

Abstract

A series of water-soluble naphthyl terminal-decorated dendrimers G0-3NapH were synthesized. Fluorescence studies reveal that strong interactions among peripheral chromophores occur in these dendrimers according to the intensive excimer emission and the low fluorescence quantum yields (Phi(f) = 0.12, 0.097, 0.065, and 0.062 for G0-3NapH). Through assembly of dendrimer with cucurbit[7]uril (CB[7]), the well-defined pseudorotaxane assemblies GnNapH x xCB[7] (x = 4, 8, 16, 32 for n = 0-3, respectively) form and the energy dissipation is entirely suppressed, resulting in a dramatic increase of the fluorescence quantum yields of dendrimers (Phi(f) = 0.18, 0.19, 0.19, and 0.20 for 0-3 generations, respectively). The noncovalent modification is a reversible process, and CB[7] can be unthreaded from the dendrimer periphery by adding 1-amimoadamantane, which can form a more stable complex with CB[7]. Furthermore, 9-anthracenecarboxylic acid (AN), an energy acceptor, was introduced into the dendritic system to investigate the harvested energy utilization. Steady-state fluorescence investigations demonstrate that the energy transfer efficiencies from naphthyl to AN in G3NapH x 32 CB[7]-AN and G2NapH x 16 CB[7]-AN are enhanced 100 and 70% compared with those without CB[7] complexation. This study provides a new strategy for developing controllable light-harvesting or -emitting dendritic systems.