pH-Induced Intramolecular Quenching. Ligand-Bridged Complexes Containing Osmium and Ruthenium

摘要

In the ligand-bridged complex ((tpy)(bpy)Os(II)(4,4'bpy)Ru(II)(H2O)(bpy)2)4+(tpy is 2,2':6',2 -terpyridine; bpy is 2,2'- bipyridine; 4,4'bpy is 4,4'-bipyridine) and its mixed-valence analogue, pH-induced photophysical effects are observed which are triggered by proton loss from the bound aqua ligand. In the Os(II)-Ru(II)(H2O) complex, Ru(II)-->bpy metal to ligand charge transfer (MLCT) excitation is followed by rapid, efficient energy transfer to the lower energy Os(III)(tpy.-) MLCT state. If the pH is raised so that ((tpy)(bpy)Os(II)(4,4'-bpy)Ru(II)(OH)(bpy)2)3+ is the dominant form, the Os(III)tpy.-based emission is quenched by the Ru(II)(OH) site. The mixed-valence complex ((tpy)(bpy)Os(III)(4,4'-bpy)Ru(II)(H2O)(bpy)2)(5+) can be converted from this nonemitting, Os(III)-Ru(II)(H2O), form, to its emitting form, ((tpy)(bpy)Os(II)(OH)(bpy)2)4+, by using pH changes to adjust the electronic distribution in the ground state. Reprints. (AW)