their photophysical properties are compared with a corresponding new monometallic species , indicating oxidative quenching . the related intramolecular electron transfer within these dyads occurs despite the presence of saturated cyclobutane rings .
for the first time oxidative quenching of osp2n4 chromophores by reactive ptii or pdii sites containing cis , trans , cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane ( dppcb ) is directly observed despite the presence of a saturated cyclobutane backbone  bridge  . 
 this dramatic effect is measured as a sudden temperature - dependent onset of a reduction in phosphorescence lifetime in [ os(bpy)2(dppcb)mcl2](sbf6)2 ( m  =  pt , 1 ; pd , 2 ) . 
 the appearance of this additional energy release is not detectable in [ os(bpy)2(dppcbo2)](pf6)2 ( 3 ) , where dppcbo2 is cis , trans , cis-1,2-bis(diphenylphosphinoyl)-3,4-bis(diphenylphosphino)cyclobutane . obviously , the square - planar metal centers in 1 and 2 are responsible for this effect . in line with these observations , the emission quantum yields at room temperature for 1 and 2 
 are drastically reduced compared with 3 . since this luminescence quenching implies strong intramolecular interaction between the osii excited states and the acceptor sites and depends on the metalmetal distances , also 
 the single crystal x - ray structures of 13 are given .