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A series of monometallic and homo- and hetero-bimetallic RuII and OsII complexes with the polyphosphines 1,1′-bis(diphenylphosphino)ethene (bppe) and 1,1′,3,3′-tetrakis(diphenylphosphino)allene (tppa) have been prepared and characterized by 31P-{1H} NMR spectroscopy, elemental analysis and fast atom bombardment mass spectral analysis. Their ground-state properties (including electrochemical behavior and electronic absorption) and excited-state properties (including luminescence, quantum yields and MLCT excited state lifetimes) are reported herein. All complexes exhibit room-temperature luminescence, with long-lived 3MLCT excited states observed for monometallic and homobimetallic OsII complexes with both bppe and tppa ligands. In the heterobimetallic RuII–OsII complex [Ru(bpy)2(µ-tppa)Os(bpy)2][PF6] (bpy 4;= 4;2,2′-bipyridine) the luminescence of the Ru(bpy)2-based unit is quenched by the connected Os(bpy)2-based unit via energy transfer across the tppa spacer containing the allene bridge. Two overlapping one-electron oxidations, corresponding to the two MII-based moieties (M 4;= 4;Ru or Os) bridged by the tppa spacer, are observed in the homobimetallic complexes.