Intramolecular interactions and photoinduced electron transfer in isoalloxazine-naphthalene bichromophores

The synthesis, the structural characterization and electrochemical and photophysical properties of new linear (OFn) and macrocyclic (MFn) bichromophoric systems containing one flavin and one naphthalene moiety, separated by (CH2)n alkyl chains (n = 4 or 6), are reported. The electrochemical properties of OF4, OF6, MF4, MF6 were investigated by cyclic voltammetry (CV) in ultra-dry THF and compared with the model compounds containing either the flavin unit (FL6) or the monomethoxy- (mona) and dimethoxy naphthalene (dmona) derivatives, respectively. While only minor ground-state interactions were evidenced between the chromophores in the voltammetric curves and absorption spectra of bichromophores, luminescence data evidenced intramolecular photoinduced electron transfer processes as main deactivation routes of flavin-centered excited states. The rates of the intramolecular photoinduced electron transfer, involving the oxynaphthalene moieties as electron donors, were finally determined.