From red to near infra-red OLEDs: the remarkable effect of changing from X = -Cl to -NCS in a cyclometallated [Pt(N^C^N)X] complex {N^C^N = 5-mesityl-1,3-di-(2-pyridyl)benzene}

[PtL(6)X] {X = Cl or NCS and L(6) = 5-mesityl-1,3-di(2-pyridyl)-benzene} display similar luminescence in solution but, in the solid state, the packing of the molecules is different, with short PtPt interactions for X = NCS, leading to a red-shifted emission band. The effect has been used to generate OLEDs that emit squarely in the NIR region (855 nm).