Excited state processes of dinuclear Pt() complexes bridged by 8-hydroxyquinoline

Dinuclear d 8 Pt( ii ) complexes, where two mononuclear square planar Pt( ii ) units are bridged in an "A-frame" geometry, possess photophysical properties characterised by either metal-to-ligand-(MLCT) or metal-metal-ligand-to-ligand charge transfer (MMLCT) transitions determined by the distance between the two Pt( ii ) centres. When using 8-hydroxyquinoline (8HQH) as the bridging ligand to construct novel dinuclear complexes with general formula [C^NPt(μ-8HQ)] 2 , where C^N is either 2-phenylpyridine ( 1 ) or 7,8-benzoquinoline ( 2 ), triplet ligand-centered ( 3 LC) photophysics results echoing that in a mononuclear model chromophore, [Pt(8HQ) 2 ] ( 3 ). The lengthened Pt-Pt distances of 3.255 Å ( 1 ) and 3.243 Å ( 2 ) results in a lowest energy absorption centred around 480 nm assigned as having mixed LC/MLCT character by TD-DFT, mirroring the visible absorption spectrum of 3 . Additionally, 1 and 2 exhibit 3 LC photoluminescence with limited quantum yields (0.008) from broad transitions centred near 680 nm. Photoexcitation of 1-3 leads to an initially prepared excited state that relaxes within 15 ps to a 3 LC excited state centred on the 8HQ bridge, which then persists for several microseconds. All the experimental results correspond well with DFT electronic structure calculations. Two novel dinuclear Pt( ii ) complexes featuring 8-hydroxyquinoline bridges were synthesized and found to have photophysical properties dominated by ligand-centered transitions mirroring that of a mononuclear model system, [Pt(8HQ) 2 ].