Photoinduced Energy Transfer Processes in Triptycene-Based Multichromophoric Arrays

The conversion of solar energy into fuel by artificial photosynthetic systems is certainly one of the most important goal in present and future chemical research. In this context, systems able to work as antennas for light harvesting are of central interest. The use of antenna systems, thanks to their collecting light activity, may also be extended to different applications, e.g. from artificial photosynthesis to signal amplification in luminescence sensors, to photodynamic cancer therapy, electroluminescent devices, dye-sensitized solar cells and light-driven photochemical molecular devices. Efficient antenna systems can be obtained with supramolecular arrays suitably organized in energy and space, with the ability to control the rate and direction of the excitation energy flow among the system components. An important thrust of current work is driven by the need of a scaffold module not only able to orient the active units in space but also able itself to act as photoactive partner inside the supramolecular array [1]. In this communication we report on the optical properties and energy transfer features of a series of hybrid organic-inorganic supramolecular arrays based on a triptycene core (Fig. 1). The systems under investigation contain one Os(II) polypyridine and two different Ir(III) phenylpyridine units, connected to the triptycene core by rigid acetylide linkers. From spectroscopic data, it is possible to observe, upon excitation of the triptycene singlet state, fast energy transfer processes that lead to the final population of Os 3MLCT state via a multi-cascade energy flow. The likely patterns and mechanisms of photoinduced energy transfer processes in the different arrays and the role of triptycene triplet levels in the dynamics are discussed. Acknowledgements: This work has been funded by CNRS in France and by Italian CNR within the ESF-EUROCORES Programme EUROSOLARFUELS (project "SolarFuelTandem").