Deep-Red Light-Emitting Electrochemical Cells: A Novel Ruthenium Complex Approach

This study presents the synthesis and characterization of a novel ruthenium(II) complex, [Ru (bpy)₂L][PF₆]₂ (RuBPPH), where L is a π-extended phenanthroline ligand, for application in near-infrared (NIR) light-emitting electrochemical cells (LECs). The RuBPPH complex exhibits a large Stokes shift and optimal HOMO-LUMO alignment, enabling efficient charge transfer and deep-red electroluminescence with a maximum emission wavelength of 675 nm. Photophysical and electrochemical analyses reveal that the extended π-conjugation of the ancillary ligand significantly enhances the device performance, achieving a maximum brightness of 2143 cd m⁻², an external quantum efficiency (EQE) of 0.62%, and a low turn-on voltage (V_on) of 3.4 V. Ligand design and ionic redistribution tune the emission properties of the LEC devices, resulting in a notable red shift in electroluminescence compared to solution-phase photoluminescence. These results highlight the critical role of ligand modification in optimizing deep-red LEC performance, offering insights for future material development. The study underscores the potential of ruthenium-based complexes in advancing NIR light-emitting technologies for biomedical and telecommunications applications.