Investigation of electron delocalization and ultrafast studies of Ru-II/Os-II dyads with ethynyl/butadiynyl-bridged polyphosphines

The redox characteristics, electronic absorption, steady-state emission, na nosecond laser flash photolysis, and a femtosecond laser spectroscopic stud y have been carried out for a series of monomeric, homobimetallic, and hete robimetallic complexes with M(bpy)(2)Cl-based moieties (M = Ru-II and Os-II ) and ethynyl- and butadiynyl-bridged polyphosphines, namely Ph2PC=CPPh2 (C 2P2) and Ph2PC=CC=CPPh2 (C4P2). These complexes were synthesized by reactio ns of the spacers with cis-M(bpy)(2)Cl-2 or by coupling reaction between tw o [Cl(bpy)(2)M(Ph2PC=CH)](PF6) (M = Ru-II, Os-II) molecules. Electronic com munication through poly-phosphine/polyyne spacers is found to decrease upon increase of the carbon chain length, and the comproportionation constant K -c was calculated as 14-18 for species with C2P2 and ca. 4 for the ones wit h C4P2,. In addition, fast intramolecular energy transfer from the Ru-II-ba sed donor to the Osl-based acceptor, with rate constant of (2.4-2.5) x 10(9 ) s(-1), occurs within heterobimetallic complexes via a Dexter-type mechani sm and an attenuation factor (beta) of 0.02 Angstrom (-1).