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

Abstract

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.

Aggregation-Induced Enhanced Emission-Active Zinc(II) β-Diketiminate Complexes Enabling High-Performance Solution-Processable OLEDs

“…Similarly, zinc­(II)­salphen complexes have been introduced in polymer light-emitting diodes, exhibiting an EQE of 3.18%, a maximum current efficiency of 6.2 cd A –1 , and a maximum power efficiency of 4.4 lm W –1 . Another Zn­(II) complex with the ethylenediamine Schiff base ligand exhibits electroluminance in the blue region, and the corresponding OLED exhibits a current and power efficacy of only 6.6 cd A –1 and 2.9 lm W –1 , respectively . A similar Zinc complex of the Schiff base ligand prepared by Gusev shows high-performance blue OLED, reaching an EQE of 5%, a current efficacy of 7.6 cd A –1 , albeit at a high operating voltage of 13.8 V .…”

“…46 Another Zn(II) complex with the ethylenediamine Schiff base ligand exhibits electroluminance in the blue region, and the corresponding OLED exhibits a current and power efficacy of only 6.6 cd A −1 and 2.9 lm W −1 , respectively. 47 A similar Zinc complex of the Schiff base ligand prepared by Gusev shows high-performance blue OLED, reaching an EQE of 5%, a current efficacy of 7.6 cd A −1 , albeit at a high operating voltage of 13.8 V. 48 It is also important to note that our device is energy-efficient as it exhibits a low turn-on-voltage (V on ) of 2.5 V, suggesting balanced carrier transport and injection. The well-aligned energy levels between m-MTDATA and Zn-I result in such favorable charge carrier and exciton generation in the device.…”

Synthesis, Structure, Spectral-Luminescent Properties, and Biological Activity of Chlorine-Substituted N-[2-(Phenyliminomethyl)phenyl]-4-methylbenzenesulfamide and Their Zinc(II) Complexes

“…Although the luminance and efficiency values of the resulting devices do not reach the maximum values for close structures [ 29 , 30 , 31 ], these preliminary results suggest that the title complexes have the potential for use as emissive layers in organic light-emitting diodes. However, the device architecture needs to be improved, by using perhaps a different host matrix, with better electron-transporting properties.…”

“…For example, based on Zn(II) complexes containing salicylaldiminate ligands, blue, greenish-white, and red emitters for organic photoelectronics with good stability and efficiency have been obtained [ 22 , 23 ]. Of particular interest are the Zn(II) complexes of azomethine ligands of 2-( N -tosylamino)benzaldehyde [ 24 , 25 ] and 3-methyl-1-phenyl-4-formylpyrazol-5-one [ 26 , 27 , 28 , 29 , 30 ] derivatives. Replacing the hydroxy group in the aldehyde fragment of azomethines with a 2-tosylamino group with the formation of the MN 4 coordination site leads to an increase in thermal stability (m.p.…”

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O′- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties

“…In particular, zinc complexes with phenanthroline and Schiff bases exhibit cytotoxicity and selectivity towards cancer cells, and are also characterized by the possibility of forming reactive oxygen species and inducing lipid peroxidation [ 10 ]. In addition to cytotoxic properties, zinc(II) compounds with various ligands exhibit antioxidant and luminescent properties [ 11 , 12 ].…”