Half-lantern Pt(II) Complexes in Deep-red Hybrid Light-Emitting Diodes

A series of Pt(II) complexes [Pt(piq)(-NS)]2 (piq = 1-phenylisoquinolinate) [NS = Spy (pyridine-2-thiolate), Spy-CF3 (5-trifluoromethylpyridine-2-thiolate), S-Q (quinoline-2-thiolate) and Spy-N (pyrimidine-2-thiolate)] are presented. They display a “half-lantern” disposition with two “Pt(piq)” fragments connected by a double pyridine thiolate bridge and remarkable short Pt-Pt distances (2.8-2.9 A). The strong bonding interaction between the Pt(II) centers endows them with bright (up to 15% Quantum Yield (QY)) deep-red (down to 740 nm) phosphorescence in both powder and PMMA coatings. Theoretical calculations based on time-dependent density functional theory (TD-DFT) point out that the nature of the emitting exciting state is related to a 3MMLCT [ds*(Pt-Pt)-pi*(piq)] transition. However, the emission shifts noticeably towards the NIR region (up to 850 nm) in solution, depending on the type of complex and the concentration. Besides, a dual emission was noted related to a high-energy 3MLCT [d(Pt)-pi*(piq)] structured emission feature and the low-energy and broad 3MMLCT emission band, highlighting the versatility of the half-lantern structure. Given their photophysical properties, the complexes were applied as color down-converting filters for the fabrication of deep-red hybrid light-emitting diodes (HLEDs), achieving external quantum efficiencies of ca. 1 %.