Coupling Chromophores to Metal and Semiconductor Nanoparticles for Energy Conversion

In this thesis work, we have investigated the interaction between molecular species and nanoparticles to realize organic-inorganic architectures able to perform complex photophysical and photoelectrochemical functions. In a first study, we have coupled an organic oligomer to silicon nanoparticles, demonstrating the ability of this system to act as a light harvesting antenna, considerably enhancing the ability of silicon nanoparticles to exploit visible light to generate its typical very long lived excited state. The high two photon absorption coefficient of the dye allows the system to be excited by NIR femtosecond pulsed light, improving the applicability of the system in high-resolution bioimaging applications. In a second study, we have performed the synthesis of a family of red-NIR emissive zinc complexes of benzodipyrrins, a little explored class of compounds, with the goal of a future integration with silicon nanoparticles to realize advanced photoactive systems. The complexes show good absorption and emission properties in an highly interesting spectral region for bioimaging and solar energy conversion. Moreover, a serendipitous chemical transformation has been observed and investigated, demonstrating its value to access a completely novel class of4 luminescent compounds. Finally, a supramolecular system composed of platinum nanoparticles coupled to a photoactive dendrimer has been synthesized and characterized, proving its ability to drive the evolution of hydrogen from water upon photoirradiation. This novel approach, thanks to the close spatial arrangement of the different components of a photosynthetic system (from the light absorbing units to the catalyst), opens the way to the realization of efficient systems with a wide variety of chromophores (exploiting the well developed chemistry of dendrimeric systems). This strategy overcomes the typical problems of diffusion based approaches, such as the necessity to use long-lived phosphorescent compounds containing expensive metals and the need of electron relays to transport electrons between the photosensizer and the catalyst.