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

Abstract

A series of oligomeric tandem terpyridyl platinum(II) complexes, namely [(^tBu₃tpy)Pt(CCtpy)PtCl](OTf)₂ (3), [(^tBu₃tpy)Pt(CCtpy)PtCC^tBu](OTf)₂ (4), [(^tBu₃tpy)Pt(CCtpy)PtCCtpy](OTf)₂ (5), and [(^tBu₃tpy)Pt(CCtpy)Pt(CCtpy)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 (ϕ = 0.43) than that in CH₃CN (ϕ < 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.