An effective strategy to obtain near-infrared emission from shoulder to shoulder-type binuclear platinum(ii) complexes based on fused pyrene core bridged isoquinoline ligands

Abstract

With the meteoric progress of near-infrared (NIR) emission materials for solution-processed polymer light-emitting diodes (PLEDs), exploring efficient NIR materials is still a key science issue. Herein, acceptor (A)–donor (D)–acceptor (A) rigid backbone 2,7-di(isoquinolin-1-yl)pyrene (BIQPy) as a cyclometalated ligand was treated with the anion of dipivaloyl methane (DPM) to afford a novel shoulder to shoulder-type binuclear platinum(II) complex, (BIQPy)[Pt(DPM)]₂; the complex and its mononuclear analogue (BIQPy)Pt(DPM) were successfully strategically designed and synthesized. The photophysical, electrochemical and electroluminescent performances of complexes were primarily systematically studied. Upon introducing a second platinum(II) ion, the relevant binuclear platinum(II) complex displays notably red-shifted emission characteristics. Strong deep-red (DR) emission at 630 nm with a quantum efficiency (Φ_PL) of 21.44% and a lifetime of 0.45 μs is obtained in (BIQPy)Pt(DPM) solution. Conversely, an outstandingly red-shifted NIR emission at 704 nm with a Φ_PL of 16.94% and a lifetime of 0.39 μs is observed in (BIQPy)[Pt(DPM)]₂ solution. Solution-processed PLEDs employing (BIQPy)Pt(DPM) as a dopant exhibit a stable electroluminescence (EL) emission of 630 nm and a shoulder at around 672 nm in the DR area, along with an efficient external quantum efficiency (EQE) of 8.84% and a brightness of 3328 cd m⁻². Encouragingly, an NIR emission peak at 700 nm with an efficient EQE of 6.06% and a radiance of up to 24 259 mW Sr⁻¹ m⁻² was observed in (BIQPy)[Pt(DPM)]₂-doped PLEDs. Results demonstrate that high-efficiency NIR-emitting binuclear platinum(II) complexes can be afforded by designing a shoulder to shoulder-type N^C–C^N tetradentate cyclometalating ligand with a fused rigid planar ligand.