Chapter 10:Interlocked Artificial Photosynthetic Model Systems Composed of Electron-Donor and [60]Fullerene Units

This chapter summarises the work carried out in the past 15 years on the synthesis and photophysical properties of organic photosynthetic model systems in which electron-donor groups are mechanically linked to fullerenes, usually [60]fullerene (C60), in topologically diverse interlocked architectures. The chapter focuses particularly on rotaxanes, in which a chain with bulky end groups passes through a macrocyclic ring, and catenanes, with two or more interlocked rings. The special techniques used for efficient synthesis of these large supramolecular systems involves molecular recognition and self-assembly based on hydrogen bonding, π–π interactions, and coordination to metal cations, most importantly Cu+. The goal of research in this area has been to manipulate interlocked organic structures through synthesis so as to maximise the lifetimes of charge-separated states produced upon excitation using light corresponding to the solar spectrum. The ways in which interlocked systems can be structurally manipulated using external stimuli so as to alter positions of noncovalently linked electron-donor (D) and electron-acceptor (A) groups will be described, including shuttle motions in D–A rotaxanes. While much of the discussion concerns rotaxanes with a C60 moiety, for which numerous synthetic protocols have been developed, the last section focuses on D–A catenanes containing C60, which are much more challenging synthetic targets. It has recently been demonstrated that photoinduced electron transfer takes place in a zinc(II)porphyrin-C60[2]catenane through an intervening Cu(I) complex that was used to assemble the system, to generate a charge-separated state whose lifetime is in the microsecond time domain.