​Natural processes of photosynthesis have increasingly inspired the fabrication of nanostructured molecular materials with advanced light-harvesting and electron-transfer features. [1-4] In this context, supramolecular chemistry allows diverse and disparate molecular building blocks to be amalgamated into highly ordered architectures through the process of self-assembly. These mimic the key functions of the photosynthetic reaction center; light harvesting, charge separation, charge transport, energy transfer, and catalysis. [5,6] Porphyrinoids, the basic building block of chlorophylls, have emerged as an exceptional class of light harvesters and electron donors in such supramolecular electron donor-acceptor hybrids [7-10]. A variety of significant applications from solar cells, hydrogen production to medical applications have been reported.

References:

1. M. R. Wasielewski, Chem. Rev., 1992, 92, 435-461.
2. R. E. Blankenship, Molecular Mechanisms of Photosynthesis, Blackwell Science, Oxford, U.K., 2002.
3. D. Gust, T. A. Moore and A. L. Moore, Acc. Chem. Res., 1993, 26, 198-205.
4. T. Nakanishi, Supramolecular Soft Matter, Applications in Materials and Organic Electronics, 2011.
5. D. M. Guldi, Chem. Soc. Rev., 2002, 31, 22-36.
6. F. D’Souza, Handbook of Carbon Nanomaterials, Synthesis and Supramolecular Systems, 2011.             
7. M. K. Panda, K. Ladomenou, and A. G. Coutsolelos, Coord. Chem. Rev. 256, (2012), 2601-2627.
8. K. Ladomenou, M. Natali, E. Iengo, F. Scandola, G. Charalampidis, A. G. Coutsolelos Coord. Chem. Rev., 304-305, 2015, 38-54.
9.  C. Stangel, C. Schubert, S. Kuhri, G. Rotas, J.T. Margraf, E. Regulska, T. Clark, T. Torres, N. Tagmatarchis, A. G. Coutsolelos, D. M. Guldi. Nanoscale 2015, 7, 2597-2608.
10.  V. Nikolaou, K. Ladomenou, G. Charalambidis, A. G. Coutsolelos, Coord. Chem. Rev. 306 (2016) 1–42.

Metal mediated polymerizations can be initiated from particle surfaces to provide nanocomposite materials with uniquely interesting compositions. Two logical systems with end-functional coupling agents that can be chosen to provide initiating ligands for this work are thiols on gold and silanes on silica. One might expect given the wealth of literature that the major difficulties in utilizing either system for this purpose had been overcome.  Unfortunately several tools appropriate for gold nanoparticles are not effective for silica nanoparticles and vice versa. Nonetheless we have prepared well defined structures using surface initiated polymerizations from gold and silica nanoparticles where the polymerizations have been mediated by either ruthenium alkylidenes or titanium alkoxide organometallic species.

Efforts in our laboratory have also shown that the rate of initiation is sensitive to the structure of a layer of tethered initiators when polymerizations are initiated from particle surfaces.  The results of this range from broadened molecular weight distributions to no polymerization at all.  It is also desirable to make the polymerization chemistry independent of the nature of the substrate.  Both of these issues can be addressed through manipulation of the surface coverage containing the tethered initiator.