Guest-host interaction of C$_{60}$ adsorbed on an ordered layer of phthalocyanine derivatives

Symmetrically substituted phthalocyanines (Pcs) with eight peripheral di-(tert-butyl)phenoxy (DTPO) groups self-organize on noble metal substrates. The rotational degrees of freedom, specific for the DTPO substituents, allow a bowl-like conformation of the Pc derivatives and thus, hosting of the C$_{60}$ molecules in two clearly distinguishable binding sites. Moreover, controlled manipulation of the C$_{60}$ by the STM tip enables switching from one site to the other. Since Pcs are well-known electron donors and C$_{60}$ molecules are good acceptors, it can be conceived as a system with two morphologically different donor-acceptor complexes, individually addressable by an STM tip. Preliminary STS analysis shows vast differences in the electronic properties. Exploration of such a system is of great interest because of its similarity to fundamental biological processes (photosynthesis, respiration), as well as its potential for application in energy storage, conversion, nanoelectronics, etc.