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) 2 L][PF 6 ] 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.