Schiff Base Zinc(II) Complexes as Promising Emitters for Blue Organic Light-Emitting Diodes

Organometallic blue
fluorescent Zn­(II) Schiff base complexes are
synthesized and explored computationally in order to use them in organic
electroluminescent heterostructures. Characterization of these pyrazolone-based
azomethine–zinc complexes was accomplished by various physicochemical
techniques to get insight into their applicability as an active layer
in light-emitting diodes. All the complexes demonstrate high thermal
stability and remarkable photoluminescence both in solution and in
the solid state with maximum in the blue region. Quantum chemical
calculations of the first exited electronic state and vertical singlet–singlet
electronic transitions by means of time-dependent density functional
theory calculations and results show that the origin of the luminescence
for the target complexes refers to the intraligand charge transfer
within the Schiff bases. The constructed light-emitting diodes demonstrate
low input voltage (3.2–4.0 V), brightness at a level of 4300–11,600
Cd m–2, and external quantum efficiency of up to
3.2%, which is a good value for purely fluorescent organic light-emitting
diodes.