Deep red light-emitting electrochemical
cells were prepared based
on a blend of [Ru(bpy)
3
]
2+
, a cationic complex,
and a neutral Zn(II)-complex based on diphenylcarbazone ligands, named
Zn(DPCO). The crystal structure of the Zn(DPCO)
2
(bpy)]
molecule revealed that the DPCO ligand has been deprotonated to form
DPCO
–
and coordinated to the Zn center metal through
the C=O and N=N moieties of DPCO. From the cyclic voltammetry
results and controlled potential coulometry data of the diphenylcarbazide
(DPC) ligand, it is possible to establish that DPC is oxidized in
an irreversible process at +0.77 V, giving DPCO and later oxidized
at a higher potential (+1.32 V) to produce diphenylcarbadiazone (DPCDO).
A detailed assignment of UV–vis spectra futures to determine
the origin of ground- and excited-state transitions was achieved by
time-dependent density functional theory calculations, which showed
good agreement with the experimental results. Using a simple device
architecture, we obtained deep red electroluminescence (EL) with high
brightness (740 cd m
–2
) and luminous efficiency
of 0.39 cd/A at a low turn-on voltage of 2.5 V. The favorable configuration
of the cell consists of only a blend of complexes of indium tin oxide
as the anode electrode and molten alloy cathode (Ga/In) without any
polymer as the transporting layer. The comparison between [Ru(bpy)
3
]
2+
and [Ru(bpy)
3
]
2+
/Zn(DPCO)
demonstrates a red shift in the EL wavelength from 625 to 700 nm in
the presence of Zn(DPCO), revealing the importance of using blends
for future systems.