Dinuclear platinum(ii) complex dominated by a zig-zag-type cyclometalated ligand: a new approach to realize high-efficiency near infrared emission

Abstract

Two new zig-zag type di- and mono-nuclear platinum(II) complexes of (BuPh-BDIQ)Pt₂(dpm)₂ and (BuPh-BDIQ)Ptdpm were synthesized and characterized by using a zig-zag type cyclometalating ligand 3,10-di(tert-butyl)-5,12-bis(4-(tert-butyl)phenyl)-benzodiisoquinoline (BuPh-BDIQ). Their single-crystal structures, and photophysical, electrochemical and electroluminescent properties were primarily investigated. Compared with (BuPh-BDIQ)Ptdpm, (BuPh-BDIQ)Pt₂(dpm)₂ exhibited a significantly increased photoluminescent efficiency of 3.64% and a red-shifted near-infrared (NIR) emission peak at 718 nm owing to its enhanced rigid planar structure in a nitrogen atmosphere. As a result, only (BuPh-BDIQ)Pt₂(dpm)₂ presented NIR electroluminescent emission in a doped polymeric light-emitting diode. The highest external quantum efficiency of 0.97% and a radiant intensity of 146 μW cm⁻² were observed for the device at 2 wt% dopant concentration, which is higher than the values of previous NIR-emitting di-nuclear platinum complexes constructed with cyclometalated ligands. Furthermore, efficiency roll-off was efficiently inhibited. This indicates that high-efficiency NIR-emitting di-nuclear platinum complexes can be obtained by designing a zig-zag type C^N–C^N tetradentate cyclometalating ligand with a big rigid planar saw band.