A photoactive molecular triad as a nanoscale power supply for a supramolecular machine

A tetrathiafulvalene-porphyrin-fullerene (TTF-P-C-60) molecular triad, which generates electrical current by harnessing light energy when selfassembled onto gold electrodes, has been developed. The triad, composed of three unique electroactive components, namely, 1) an electron-donating TTF unit, 2) a chromophoric porphyrin unit, and 3) an electron-accepting C-60 unit, has been synthesized in a modular fashion. A disulfide-based anchoring group was tagged to the TTF end of the molecule in order to allow its selfassembly on gold surfaces. The surface coverage by the triad in a self-assembled monolayer (SAM) was estimated to be 1.4 nm(2) per molecule, a density which is consistent with hexagonal of a pi-electron-deficient tetracationic cyclobis(paraquat-p-phenylene) (CBPOT4+) cyclophane and a pi-electron-rich 1,5-bis[(2-hydroxyethoxy)ethoxy] naphthalene (BHEEN) thread. The redox-induced dethreading of the CBPQT(4+) cyclophane from the BHEEN thread can be monitored by measuring the increase in the fluorescence intensity of the BHEEN unit. A gradual increase in the fluorescence intensity of the BHEEN unit concomitant with the photocurrent generation, even at a potential (OV) much lower than that required (-300mV) for the direct reduction of the CBPQT(4+) unit, confirms that the dethreading process is driven by the photocurrent generated by the triad-SAM.