Deep-blue phosphorescence from platinum(ii) bis(acetylide) complexes with sulfur-bridged dipyridyl ligands

Abstract

New approaches to prepare rarer emitters such as those that are deep-blue are needed to advance OLED technologies. Here, we demonstrate that a series of new platinum(II) bis(acetylide) complexes [Pt(N–N)(CCPh)₂] containing sulfur-bridged dipyridyl ligands (N–N) with various sulfur oxidation states: sulfide (S), sulfoxide (SO) and sulfone (SO₂) give access to variable emission colors from green to deep-blue. Spectroscopic, electrochemical and computational studies show that mixed character excited states have energies which are significantly influenced by the oxidation state of sulfur and the presence of substituents. The sulfide and sulfoxide complexes are non-emissive in the solution state, while the sulfone complexes display ³MLCT/³LLCT excited-state yellow phosphorescence. In PMMA films the sulfide and sulfoxide complexes show intense deep-blue phosphorescence and green phosphorescence for the sulfone complexes, with photoluminescence quantum yields ranging from 0.35–0.91. Here we demonstrate the capability of changing the photophysical properties of these metal emitters by varying the oxidation state of sulfur to achieve intense deep-blue and green emitters.