Unprecedented conformational modulation of the efficiency of luminescence in Ru(II) bipyridyl complexes containing a bis(bidentate) phosphine

We report the first observation of conformational modulation of the efficiency of luminescence of a chelating phosphine containing a saturated backbone and combined with [Ru(bpy)2]2+. The observed luminescent lifetimes are very long: 910(20) ns in CD3CN and 794(20) ns in CH3CN at 298 K. The bimetallic structure of rac-(ΔΔ/ΛΛ)-[Ru2(dppcb)(bpy)4](PF6)4 (1) and meso-(ΔΛ/ΛΔ)-[Ru2(dppcb)(bpy)4](PF6)4 (2), where dppcb is cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane, is responsible for this dramatic effect. An enhanced folding of the cyclobutane rings drastically reduces the efficiency of luminescence as observed in the new monometallic complexes [Ru(dppcb)(bpy)2](PF6)2 (3) and [Ru(dppcbO2)(bpy)2](PF6)2 (4), where dppcbO2 is cis, trans, cis-1,2-bis(diphenylphosphinoyl)-3,4-bis(diphenylphosphino)cyclobutane.