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Artificial light, once a luxury, has become central to modern life, with its evolution spanning from fire to LEDs. Now, researchers have developed a new class of efficient light-emitting materials as promising candidates to be applied to lighten the darkness. They demonstrated easily accessible aluminum-based organometallic complexes that have the potential to be applied in optoelectronic devices.

The research team is from the Institute of Â鶹ÒùÔºical Chemistry, Polish Academy of Sciences in Warsaw and Warsaw University of Technology led by Prof. Janusz LewiÅ„ski in collaboration with Prof. Andrew E. H. Wheatley from Cambridge University. The paper is in the journal Angewandte Chemie International Edition.

Growing demand for artificial light spurred the development of energy-efficient solutions like fluorescent lamps and, later, light-emitting diodes (LEDs). 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.

Aluminum, 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)aluminum) in LEDs in 1987, aluminum-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.

Drawing inspiration from earlier work and benchmark materials like Alq₃, the researchers synthesized a new series unique tetrameric chiral-at-metal alkylaluminum anthranilates [(R′-anth)AlR]₄ incorporating common anthranilates as a core ligand. These aluminum-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 aluminum-stereogenic tetranuclear complexes that happen to have unique properties," claims Vadim Szejko, the first author of the work.

Comprehensive physicochemical studies, including detailed analysis of photoactivity, revealed that the aluminum-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 for aluminum complexes," remarks Dr. 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.

The work is an important step forward in 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 making it useful in practical applications, especially in technologies like OLEDs, display screens, and sensors.