Investigation of Electron Delocalization and Ultrafast Studies of RuII/OsII Dyads with Ethynyl/Butadiynyl-Bridged Polyphosphines

The redox characteristics, electronic absorption, steady-state emission, nanosecond laser flash photolysis, and a femtosecond laser spectroscopic study have been carried out for a series of monomeric, homobimetallic, and heterobimetallic complexes with M(bpy) 2 Cl-based moieties (M = Ru II and Os II ) and ethynyl- and butadiynyl-bridged polyphosphines, namely Ph 2 PC⋮CPPh 2 ( C 2 P 2 ) and Ph 2 PC⋮CC⋮CPPh 2 ( C 4 P 2 ). These complexes were synthesized by reactions of the spacers with cis -M(bpy) 2 Cl 2 or by coupling reaction between two [Cl(bpy) 2 M(Ph 2 PC⋮CH)](PF 6 ) (M = Ru II, Os II ) molecules. Electronic communication through polyphosphine/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 C 2 P 2 and ca. 4 for the ones with C 4 P 2 . In addition, fast intramolecular energy transfer from the Ru II -based donor to the Os II -based acceptor, with rate constant of (2.4−2.5) × 10 9 s -1, occurs within heterobimetallic complexes via a Dexter-type mechanism and an attenuation factor (β) of 0.02 Å -1 .