A feasible approach to obtain near-infrared (NIR) emission from binuclear platinum(II) complexes containing centrosymmetric isoquinoline ligand in PLEDs

Abstract Organic light-emitting diodes (OLEDs) of deep-red (DR)/near-infrared (NIR) emission have become an emerging hot topic in applications for medical and night-vision devices. In this article, one novel symmetrical binuclear platinum(II) complexes as well as its mononuclear analogues, namely (DIQB)[Pt(DPM)]2 and (DIQB)Pt(DPM), involving big rigid planar ligand 1,4-di(isoquinolin-1-yl)benzene (DIQB) and auxiliary ligand dipivaloylmethanato (DPM), were successfully synthesized and characterized. Intrinsic DR emission peaked at 618 nm with a photoluminescence quantum yield (Φ) of 2.42% and lifetime of 0.37 μs was obtained in the (DIQB)Pt(DPM) solution. Wondrously, an outstandingly 112 nm red-shifted emission peaked at 730 nm with a Φ of 0.77% and lifetime of 0.26 μs was observed in (DIQB)[Pt(DPM)]2 solution. Density functional theory (DFT/TD-DFT) calculations were carried out to reveal the emission process and a predominant 3ILCT/3MLCT characteristics. As a result, the emission of platinum(II) complexes is tuned from DR to NIR via appending an additional platinum(II) ion. OLEDs based on (DIQB)Pt(DPM) exhibited an efficient DR emission at 666 nm with a maximum external quantum efficiency (EQE) of 2.86% and a brightness of 1632 cd/cm2 at dopant concentration of 3 wt %, In contrast, an outstandingly 80 nm red-shifted NIR emission at 746 nm with a EQE of 0.58% and a radiance of up to 10036 mW/Sr/m2 was obtained for the (DBIQ)[Pt(DPM)]2 device at the same dopant concentration. Moreover, the efficiency roll-off was efficiently inhibited in the (DIQB)[Pt(DPM)]2-doped devices. This work demonstrates that binuclear platinum(II) complexes dominated by centrosymmetric type CˆN-CˆN tetradentate big rigid planar ligand is an effective strategy for obtaining NIR luminescent materials.