Alkyl-Spacer Enhancement in Performance of Light-Emitting Electrochemical Cells

Synthetic, structural, photophysical, and electrochemical study of [Ir(ppy)(2)(py)(2)](BF4) (1(BF4)) and four di-N-N-bridged complexes of [Ir(ppy)(2)(bpa)](2)(BF4)(2)(2A(BF4)(2)), [Ir(ppy)(2)((cis-bpe))](2)(BF4)(2)(2B(BF4)(2)), [Ir(ppy)(2)(tmp)](2)(BF4)(2)(2C(BF4)(2)), and [Ir(ppy)(2)(bpy)](4)(BF4)(4)(3(BF4)(4)) are described with Hppy = 2-phenylpyridine, py = pyridine, N-N= dipyridyl ligands of 1,2-bis(4-pyridyl)ethane (bpa),cis-1,2-bis(4-pyridyl)ethylene (cis-bpe), 1,3-di(4-pyridyl)propane (tmp), and 4,4'-dipyridine (bpy). Five single-crystal structures of1(PF6),2A(NO3)(2),2A(PF6)(2),2B(PF6)(2), and3(NO3)(4)were determined, supporting the dibridged structures and presence of a variety of stereoisomers. Application of four luminescent complexes,1(BF4),2A(BF4)(2),2C(BF4)(2), and3(BF4)(4), in solid-state light-emitting electrochemical cells (LECs) is reported. The work demonstrates an effective approach to realize efficient LECs based on dibridged di- and multinuclear cationic transition-metal complexes with a suitably long alkyl spacer in the bridging ligand.