Facile synthesis and photophysical properties of sphere-square shape amphiphiles based on porphyrin-[60]fullerene conjugates.

Molecules constructed from a combination of zero-dimensional ([60]fullerene (C60)) and two-dimensional (porphyrin (Por)) nanobuilding blocks represent an intriguing category of sphere-square "shape amphiphiles". These sphere-square shape amphiphiles possess interesting optoelectronic properties. To efficiently synthesize a large variety of C60-Por shape amphiphiles, a facile route based on Steglich esterification was developed. The synthetic strategy enables the preparation of hydroxy-functionalized Por precursors (9-12) with high purity in a one-pot procedure. All of the C60-Por shape amphiphiles (1-5) can be readily synthesized in good yields through subsequent Steglich esterification with a highly soluble carboxylic acid derivative of methanofullerene (13). Photophysical studies indicated weak electronic coupling between the C60 and Por moieties and suggest an edge-to-face alignment for the moieties. The fluorescence of electronically excited Por portions of each amphiphile was efficiently quenched, which was indicative of electron transfer from (1)Por to the C60 group(s). Increasing the number of C60 groups on the shape amphiphiles led to more pronounced quenching of the Por fluorescence, which indicated the potential for more effective generation of charge-separated species, C60(-.)Por(+.), from the photoexcited C60-Por shape amphiphiles.