Photoinduced energy- and electron-transfer processes in molecular assemblies combining phenothiazine (PTZ) donors (D), Ru(II) bisterpyridine photosensitizer (P) and fullerene (C60) acceptors (A) have been studied. A series of covalently linked dyads (i.e., D–P and P–B–A) and triads (i.e., D–P–B–A) was prepared and the donor-to-acceptor distance was varied in the range from 18 to 37 Å by using para-phenyleneethynylene bridging units (B) of different lengths. The modular synthesis of Ru(II) bisterpyridine complexes was used to incorporate donor- and the acceptor-functionalized terpyridine ligands, which resulted in linear assemblies in which the donor and the acceptor units were separated by the Ru(II) complex. The photophysical properties were investigated by steady-state and time-resolved spectroscopy. Upon light excitation of the Ru(II) complex, the emission was strongly quenched by the phenothiazine and the fullerene units. Transient absorption spectroscopy revealed characteristic absorption changes that were ascribed to a fast decay of the lowest triplet metal-to-ligand charge transfer (3MLCT) transition states of the Ru(II) complex. In the case of the dyads P–B–A, energy transfer with a distance-dependent rate constant to the lowest excited triplet state of the C60 unit was observed. On the other hand, the decay of the 3MLCT state in the dyad D–P was caused by an electron-transfer process from the PTZ unit to the Ru(II) center, which yielded a charge-separated state (CSS) between the donor and the photosensitizer. In the triads D–P–B–A, energy- as well as electron-transfer processes were observed, whereby the ratio could be controlled by the excitation wavelength and a long-lived CSS between the donor and the acceptor could be populated.

Molecular dyads and triads based on phenothiazine, Ru(II) bisterpyridine complexes and fullerene

254th National Meeting (2017)

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