Bis(pyridylpyrazolate)platinum(II): a mechanochromic complex useful as a dopant for colour-tunable polymer OLEDs

The photoluminescence and mechanochromic behaviour of the bis(3-(3,5-bis(dodecyloxy) phenyl)-(5-pyridin-2-yl) pyrazolate) platinum(II) complex PT12, selected from a series of Pt(II) compounds with N,N '-pyridylpyrazolate ligands, has been investigated. The electroluminescence properties of polymer OLEDs based on PT12-doped polyfluorene (PFO) are also described. Addition of PT12 induces the formation of the PFO beta-phase, a much more ordered phase with enhanced colour stability at high bias and high photoluminescence quantum efficiency. Additionally, the characteristic blue emission of PFO is red-shifted for PT12 concentrations equal to or higher than 3%. Depending on the dopant concentration and the applied current, the colour coordinates of these polymer OLEDs undergo a broad shift in the CIE colour space. In addition, through the strategic use of keto defect sites, white-emitting devices can be fabricated with a very small addition of PT12.