Photoinduced electronic energy transfer in modular, conjugated, dinuclear Ru(II)/Os(II) complexes

Rigid, modular heterometallic dinuclear complexes containing luminescent units have been synthesized and their photophysical properties investigated. The metal complexes are derivatives of ruthenium and osmium trisbipyridine compounds and are linked by 2, 3, 4 or 5 para-phenylene units. A fast and efficient photoinduced energy transfer takes place from the excited ruthenium moiety to the osmium-based component. The rate constants of the energy transfer processes have been determined by time-resolved emission and sub-picosecond transient absorption spectroscopy. A comparison with similar systems containing substituted polyphenylene units is made in order to clarify the role of the tilt angle between the spacers on the energy transfer rates. Such investigation confirmed that a through bond Dexter type mechanism is responsible for the process