It is foreseeable that artificial photosynthetic systems that will ultimately power practical solar fuels production must be based on molecular and supramolecular assemblies. Specific requirements that such assemblies must meet include the collection of light energy, separation of charges, and transport of charges to catalytic sites, where water oxidation and CO2 reduction will occur. Notable progress has been made on each aspect of these complex problems – yet researchers have not developed components that are both efficient and robust, and have not integrated the existing functional components into a working system. The design and development of light harvesting, photoconversion, and catalytic modules capable of self-ordering and self-assembling into an integrated functional unit will make it possible to realize efficient artificial photosynthetic systems based on nanometer scale carbon structures.
Our current research covers the timely topic of designing, devising, synthesizing, and testing novel nanometer scale structures – fullerenes, carbon nanotubes and nanoparticles – in combination with metalloporphyrins and other electron donors as integrative components for electron-donor-acceptor ensembles. These ensembles are typically probed in condensed media and at semitransparent electrode surfaces. In particular, we test a variety of covalent (i.e., nanoconjugates) and non-covalent linkages (i.e., nanohybrids) to demonstrate how to govern / fine-tune the electronic interactions in the resulting electron-donor-acceptor ensembles. In the context of covalent bridges, different spacers are considered, which range from pure “insulators” (i.e., amide bonds, etc.) to sophisticated “molecular wires” (i.e., p -phenylenevinylene units, etc.). Furthermore, we are interested in the fundamental impact that these vastly different spacers may exert on the rate, efficiency, and mechanism of short- and long-range electron transfer reactions. Additionally, a series of non-covalent motifs are studied: hydrogen bonding, complementary electrostatics, π-π stacking and metal coordination – to name a few. These motifs are successfully employed by us and our collaborators en route towards novel architectures (i.e., linear structures, tubular structures, rotaxanes, catenanes, etc.) that exhibit unique and remarkable charge transfer features.
Our largely interdisciplinary strategy focuses on well-defined molecular architectures: we start with building blocks (i.e., at an atomic and / or molecular scale) that give access to a priori design of multifunctional molecular materials and their integration into 2- or 3-dimensional solid electron-donor-acceptor ensembles.