Artificial light has become central to modern life, with its evolution spanning from fire to LEDs. Now, researchers from the Institute of Physical Chemistry, Polish Academy of Sciences in Warsaw and Warsaw University of Technology led by Janusz Lewiński in collaboration with Andrew E. H. Wheatley from Cambridge University have developed a new class of efficient light-emitting materials as the promising candidates to be applied to lighten the darkness. They demonstrated easily accessible aluminium-based organometallic complexes that have the potential to be applied in optoelectronic devices.

Once production costs dropped, LEDs became ubiquitous in homes and portable devices. Today, researchers pursue even more efficient technologies such as organic LEDs (OLEDs) and novel fluorescent materials. Fluorophores based on main-group metal complexes have attracted considerable interest in recent years, where their development is driven by the possibility of the practical potential application in optoelectronic devices, chemosensors or bioimaging. Aluminium, being abundant, lightweight, and conductive, is gaining attention as an alternative to rare or toxic metals. Since the breakthrough use of Alq₃ (tris(8-hydroxyquinolinato)aluminium) in LEDs in 1987, aluminium-based complexes have been explored for their promising photophysical properties, particularly in OLEDs and light-emitting sensors. Nowadays, researchers are actively seeking novel and more efficient materials to enhance lighting technologies.

Recently, the researchers have developed a new class of highly-luminescent organoaluminium complexes. Drawing inspiration from earlier work and benchmark materials like Alq₃, the researchers synthesized a new series unique tetrameric chiral-at-metal alkylaluminium anthranilates [(R′-anth)AlR]₄ incorporating common anthranilates as a core ligand. These aluminium-based complexes demonstrate promising optoelectronic properties due to the coordination between the metal core and tailored ligands. “In this work, we focus on commercially available anthranilic acid (anth-H₂) and its N- methyl (Me-anth-H₂) and N-phenyl (Ph-anth-H₂) derivatives, as model proligands. The reaction between each of these acids and appropriate R₃Al compound in toluene has resulted in the formation of a series of aluminium-stereogenic tetranuclear complexes that happen to have unique properties”, claims Vadim Szejko.

Comprehensive physicochemical studies, including detailed analysis of photoactivity, revealed that the aluminium-based anthranilates exhibit photoluminescence quantum yields of up to 100 % in the solid state, enabled by their unique electronic structure and non-covalent interactions that stabilize excited states. Subtle ligand modifications were shown to significantly boost emission efficiency, opening new pathways for designing advanced photoactive materials. These findings contribute valuable insight into the still underexplored photochemistry of multinuclear complexes and their potential applications in optoelectronics.

“By changing the N-substituents from H to Me and Ph, we have developed a series of luminophores that exhibit poor-to-excellent performance, providing a [(Ph-anth)AlEt]₄ derivative that achieves a unity photoluminescence quantum yield in the condensed phase, which is unprecedented foraluminium complexes”, says Iwona Justyniak. Quantum-chemical calculations provided insights into the nature of electronic transitions and identified specific fragments at the molecule level that most strongly contribute to the material’s photophysical properties. Ligand modifications suppressed unwanted relaxation pathways, enhancing emission efficiency. In the solid state, non-covalent intra- and intermolecular interactions help preserve structural integrity during excitation, minimizing distortions that would otherwise reduce fluorescence. Moderate molecular aggregation adds rigidity, supporting high luminescence.

This work is an important step forward the design of the novel, easily accessible effective fluorescent materials. The simplicity of the ligand framework modification offers the possibility of further upgrading of the system to achieve greater chemical stability and enables modulation of the optical properties which brings us closer to make it useful in practical applications, especially in technologies like OLEDs, display screens, and sensors. (Source: IPC PAS)

Reference: V. Szejko et al.: Luminescent Alkylaluminium Anthranilates Reaching Unity Quantum Yield in the Condensed Phase, Ang. Chem. 64, e202501985 (2025); DOI: 10.1002/anie.202501985

Link: Organometallic and Materials Chemistry, Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland