Nanostructured materials as template for porphyrin J- aggregates

The widespread interest into organic- inorganic hybrid nanocomposites takes advantage by the emergence of new optical properties and chemical behavior, both in solution and on solid surface, coming from the conjunction of chemically different building blocks. This class of materials have been extensively exploited in several scientific fields, as imaging, catalysis, photonics and optoelectronics. In this framework, due to their interesting spectroscopic properties and their ability to form self-assembled structures, porphyrins represent interesting candidates as organic building blocks to realize hybrids nanocomposite materials. In particular, tetrakis (4- sulphonatophenyl) porphyrin (TPPS4) is an intriguing compound due to its ability to form self- assembled J- aggregates with different shape and size extremely dependent on the experimental conditions as, pH medium, reactant concentrations, addition of salt and templating agents [1-2]. Here, wefocus on the TPPS4 aggregation process assisted and/or catalyzed by the presence of inorganic nanostructured materials such as gold nanostructures and carbon nanotubes (CNTs). Our goal is to build up new hybrids nanocomposites, whose properties merge the optical and photophysical properties of organic and inorganic nanostructures. Exploiting the class of metallic nanosized materials, we have chosen gold nanorods (Au NRs) and clusters composed of ten atoms (Au10). The presence of Au NRs prompts the formation of highly ordered structures of porphyrins in solution whereas J-aggregates trigger the interaction among Au NRs leading to the formation of a J-aggregates/ Au NRs nanohybrid material [3]. Self- assembled structures can be also formed in the presence of Au10 clusters, obtaining nanohybrid materials composed of nanostructured gold and the aggregated porphyrin both in solution and on glass surface. Experimental findings have shown the growth of Au10 clusters forming a metallic layer on the glass surface whose properties are strictly related to experimental conditions. The optical and photophysical properties of these components make them interesting candidates for a range of potential applications. Moreover, the aggregation process has also been examined in the presence of amine functionalized CNTs showing the importance of the alkyl chain length and the number of amine groups in promoting the porphyrin aggregation process. All the investigated nanocomposites have been examined by a detailed spectroscopic and morphologic characterization in solution and on solid state.