Light-Emitting Organometallic Molecules and Materials

For the last several decades, we see the rise of organometallic N-heterocyclic carbene complexes as efficient phosphorescent emitters.  Recently, research is focused on platinum and iridium carbenes because of their potentials as blue emitters. Interest in carbenes as ligands in metal (Pt and Ir) complexes originates from their ability as sigma-donors to acquire high energy triplet excited states and short (microsecond) triplet lifetime. These photophysical properties are essential for high performance blue organic light emitting diodes (OLEDs). The deep blue emission and color purity can be achieved either by breaking conjugation or by introducing strong sigma-donor acetylide ligand in the metal carbene complexes.

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X-Ray structures of platinum(II) carbene acetylide complexes

In this project, we design and synthesise new platinum N-heterocyclic carbene acetylide complexes and investigate their photophysical properties-absorption and photoluminescence (fluorescence and phosphorescence), and the lifetime of singlet and triplet excited states. These materials emit in the blue region. Figures below show a family of Pt-carbene complexes, and their photoluminescence (PL) in solution and electoluminescene color coordinates in a solid state solid device. Our study shows that in solid state (PMMA matrics), the quantum yield of the complexes is 22-56 %, and the triplet excited states life is 9-46 microsecond. OLEDs of some of the materials show deep blue electroluminescence (EL) with external quantum efficiency (EQE) of 10-15 %. The colour purity and efficiency of the OLEDs can be tuned by changing the cabene backbone and aryl substitutents of the acetylide ligand.

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Photoluminescence and electroluminescence color coordinates of N-heterocyclic carbene complexes

Related Recent References

In Search of Deeper Blues: Trans-N-Heterocyclic Carbene Platinum Phenylacetylide as a Dopant for Phosphorescent OLEDs, ACS Appl. Mater. Interfaces 2017, 9, 47, 41111-41114. DOI: 10.1021/acs.jpca.9b07079

Blue Phosphorescent trans-N-Heterocyclic Carbene Platinum Acetylides: Dependence on Energy Gap and Conformation, J. Phys. Chem. A 2019, 123, 42, 9069-9078. DOI: 10.1021/acsami.7b12107

trans-N‑(Heterocyclic Carbene) Platinum(II) Acetylide Chromophores as Phosphors for OLED Applications, ACS Appl. Electron. Mater. DOI: org/10.1021/acsaelm.0c00064