(Invited) Subphthalocyanine-Fullerene Ensembles As Light Harvesting Systems

Abstract

A multi-SubPc hybrid comprised of a perfluorinated SubPc fused dimer (syn or anti topoisomer) axially functionalized with unsymmetrical octylthio-substituted SubPcs linked through their periphery by ethynyl linkers to the boron atoms of the dimer has been prepared. Electrochemical and steady state photophysical studies of the syn hybrid suggest the existence of an electron transfer process from SubPc units to photoexcited SubPc dimer to generate a (SubPc•+-SubPc Dimer•-) radical pair. Furthermore, the disposition that the two axial SubPc units acquire in this assembly gives rise to unique supramolecular recognition sites suitable for the complexation of shape and size complementary fullerenes. Thus, the binding ability of this hybrid towards different fullerene derivatives, namely C60, C70, C60-PCBM and C70-PCBM, has been analyzed through UV-vis absorption, fluorescence and NMR titrations. It has been demonstrated that syn compound displays a unique fullerene complexation mode. Initially, the formation of a 1:1 supramolecular complex involving the axial octylthio-substituted SubPcs embracing a guest molecule with remarkable association constants of around 106 - 105 M-1 is observed. This well-defined cavity generated by the SubPc dimer and the axial SubPcs shows higher affinity for the C70 fullerene derivatives. Then, a secondary supramolecular recognition event between the curved perfluorinated SubPc syn dimer unit and another fullerene molecule occurs, with significant binding constants of 104 - 103 M-1, depending on the size and the host-guest electrostatic interactions, leading to the formation of the final 1:2 supramolecular ensemble. Figure 1