Implementation of redox gradients in hydrogen bonded complexes containing N,N-dimethylaniline, flavin and fullerene derivatives

Abstract

A variety of supramolecular complexes were formed by associating an electron donor-substituted flavin dyad (10-[4′-(N,N-dimethylamino)phenyl]isoalloxazine: DMA–Fl) and a family of fullerene derivatives that contain single and double hydrogen bond receptors (SRC₆₀ and DRC₆₀). The stoichiometry of the corresponding complexes, that is, DMA–Fl and SRC₆₀ or DRC₆₀, were examined by Job's plot analysis of the absorption changes linked to DMA–Fl at 470 nm. To this end, 1 : 1 and 1 : 2 complex stoichiometries were determined for DMA–Fl-SRC₆₀ and (DMA–Fl)₂-DRC₆₀, respectively. Molecular aggregates in the form of remarkably stable clusters were formed by the fast injection method. Insights into these clusters came from transmission electron microscopy (TEM) measurements, which revealed network configurations for (DMA–Fl-SRC₆₀)_n with diameters in the range between 200 and 500 nm, while uniform nanoparticles of about 40 nm diameter were discernible for [(DMA–Fl)₂-DRC₆₀]_n. The highly colored composite clusters were assembled onto an optically transparent electrode covered with nanostructured SnO₂ films by the electrophoretic deposition technique. Important are the photocurrent action spectra providing maximum IPCE values that are twice as high for [(DMA–Fl)₂-DRC₆₀]_n than for (DMA–Fl-SRC₆₀)_n. To complement these studies the dynamics of electron transfer were investigated by femtosecond laser flash photolysis in the supramolecular clusters (i.e., (DMA–Fl-SRC₆₀)_n and [(DMA–Fl)₂-DRC₆₀]_n). As a matter of fact, for the first time we were able to demonstrate the unidirectional electron transfer from the terminal electron donor (N,N-dimethylaniline) moiety to the terminal electron acceptor (fullerene) moiety.