Photophysical study of spiro-bifluorene bridged Pt(II), Os(II) and Ir(III) luminescent complexes and supramolecular arrays

This paper describes expeditious stepwise synthesis of polynuclear complexes based on heteroleptic iridium(iii) and osmium(ii) fragments linked to a central Pt(ii) module via a spirobifluorene-bridge using a strategy based on the construction of preformed complexes. The luminescence features of the final multi-chromophoric array, i.e. a tetrad consisting of spirobifluorene-bridged Pt, Ir and Os complexes, have been studied by comparison with the features of reference complexes bearing two identical luminophores (Ir or Os) at the periphery. The 3MPtLCT and 3LC states of the Pt and spiro ligand undergo fast energy transfer into the 3MIrLCT or the 3MOsLCT state in the Pt-M2 (M = Ir or Os) arrays, whereas the 3LC and the 3MPtLCT states function as energy reservoirs for the metal excited states close in energy, resulting in a pronounced increase of the excited state lifetimes of these arrays. The tetrad efficiently works as an antenna system where the collected light energy is transferred to the Os unit acting as the final collector.