Transition Metal Complexes in Light Emitting Applications

Transition metal complexes have become pivotal emissive materials across a range of light-emitting technologies, from organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LEECs) to sensors and photonic devices. Their versatile coordination geometries and tunable ligand fields enable precise control over excited-state energies, emission wavelengths and photophysical lifetimes. Heavy d6 metals such as iridium(III), platinum(II) and osmium(II) have historically dominated phosphorescent emitters, achieving high internal quantum efficiencies by harvesting both singlet and triplet excitons. Recent advances extend this paradigm to more abundant first-row metals, achieving competitive luminescence and device stability. Key challenges remain in suppressing non-radiative decay pathways, managing charge-transfer character and ensuring operational longevity. Progress in ligand design, molecular aggregation control and host–guest architectures continues to drive performance towards commercial viability, offering routes to cost-effective, colour-tunable and energy-efficient light sources with broad societal impact.

Research from Nature Portfolio

Recent studies have demonstrated that strategic substitution on tetradentate platinum(II) frameworks can suppress deleterious metal–metal-to-ligand charge transfer, yielding dopant films with photoluminescence quantum yields approaching 99% and external quantum efficiencies above 26%. Device lifetimes are extended eightfold by minimising structural distortion between triplet metal-centred and ligand-centred states. In parallel, novel chromium(0) complexes have been shown to rival traditional ruthenium(II) and osmium(II) luminophores: careful ligand engineering produces metal-to-ligand charge-transfer states with long excited-state lifetimes and high photoluminescence yields, opening first-row d6 metals to both photoredox catalysis and electroluminescent applications under low-energy illumination.

Transition Metal Complexes in Light Emitting Applications publication trend

The graph below shows the total number of articles in transition metal complexes in light emitting applications across all publications each year (not limited to Nature Index journals).

Technical terms

Phosphorescence: Radiative emission from a triplet excited state to the ground state, typically longer-lived than fluorescence. Photoluminescence quantum yield (PLQY): Fraction of absorbed photons re-emitted as light. External quantum efficiency (EQE): Ratio of emitted photons to injected electrons in a device. Metal-to-ligand charge transfer (MLCT): Electronic transition involving electron density shift from metal centre to ligand orbitals. Intersystem crossing: Non-radiative transition between electronic states of different spin multiplicity.

References

1. Modified t-butyl in tetradentate platinum (II) complexes enables exceptional lifetime for blue-phosphorescent organic light-emitting diodes. Nature Communications (2024).
2. Photoredox-active Cr(0) luminophores featuring photophysical properties competitive with Ru(II) and Os(II) complexes. Nature Chemistry (2023).
3. A simple and efficient approach toward deep-red to near-infrared-emitting iridium( iii ) complexes for organic light-emitting diodes with external quantum efficiencies of over 10%. Chemical Science (2020).
4. Enhancing Molecular Aggregations by Intermolecular Hydrogen Bonds to Develop Phosphorescent Emitters for High‐Performance Near‐Infrared OLEDs. Advanced Science (2019).
5. Highly luminescent palladium( ii ) complexes with sub-millisecond blue to green phosphorescent excited states. Photocatalysis and highly efficient PSF-OLEDs. Chemical Science (2016).