Spectacular luminescent behaviour of tandem terpyridyl platinum(II) acetylide complexes attributed to solvent effect on ordering of excited states, "ion-pair'' formation and molecular conformations

A series of oligomeric tandem terpyridyl platinum(II) complexes, namely [((t)Bu(3)tpy)Pt(C equivalent to Ctpy)PtCl](OTf)(2) (3), [((t)Bu(3)tpy)Pt(C equivalent to Ctpy)PtC equivalent to(CBu)-Bu-t](OTf)(2) (4), [(tBu(3)tpy)Pt(C equivalent to Ctpy)PtC equivalent to Ctpy](OTf)(2) (5), and [((t)Bu(3)tpy)Pt(C equivalent to Ctpy)Pt(C equivalent to Ctpy)PtCl](OTf)(3) (6), were prepared and their spectroscopic properties and self-aggregating behaviour were examined. In particular, complex 4 exhibits unusually higher emission quantum yield in CH2Cl2 (phi = 0.43) than that in CH3CN (phi < 0.1), which is attributed to the formation of a "contact ion pair'' in chlorinated solvents, such as CHCl3, CH2Cl2 and C6H5Cl. DFT calculations revealed that both intersystem crossing (ISC) and radiative decay of this complex are less effective in CH3CN than in CH2Cl2, thus accounting for the low emission quantum yield in CH3CN.