Rigidified tetrathiafulvalene-[60]fullerene assemblies: towards the control of through-space orientation between both electroactive units

Our recent works on fused TTF-C-60 dyads. (TTF)(n)-C-60-polyads and C-60-TTF-C-60 dumbbell triads in which the acceptor Coo is doubly tethered to the donor tetrathiafulvalene through a rigidified cyclohexene ring are presented. This approach was developed in order to control the relative orientation as well as the distance between both donor and acceptor entities. Thereby, through-space interactions which are of great importance for photoinduced electron- and/or energy-transfer processes are expected to dominate because of the special topology of the molecules. The two linked C-60 and TTF chromophores in such adducts are not only in close proximity but also have optimal orbital orientations, thus facilitating these through-space electronic interactions. These new C-60-based assemblies were synthesized by [4 + 2] Diels-Alder cycloaddition reactions. The different methodologies considered for their synthesis are discussed. their analytical, spectroscopic characterizations and electrochemical properties are also described. The selective etectro-oxidation or reduction afforded the corresponding radical cation and radical anion which were characterized by EPR. These C-60-based assemblies were studied for their nonlinear optical and optical limiting applications. Moreover, intramolecular photoinduced charge-separation and charge-recombination processes in a fused C-60-TFF-C-60 dumbbell triad which was designed to be soluble in organic solvents were investigated by time-resolved absorption and fluorescence techniques. Appreciable interaction between the C,() moiety and TTF moiety in the ground state was suggested by steady-state absorption spectra and the fluorescence spectra showed considerable interaction in the singlet excited state. The nanosecond transient absorption spectra displayed the formation of the charge-separated radical pair C-60-TTF.+-C-60(.-). characterized by a lifetime of ca. 20 ns in benzonitrile.