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.
Highlights
Despite the significant progress achieved since the first preparation of organic light-emitting diodes (OLEDs) by Tang[1] and Burroughes,[2] the lack of cheap and processable electro-luminophores still represents immediate needs
Zinc Schiff base complexes with benzoheterocycles are of considerable interest, the synthesis of which has recently been intensified owing to their very intense blue photoluminescence emission.[22−24] In addition, the zinc complexes of azomethine ligands exhibit good electron transport ability, high fluorescence quantum yields, and excellent thermostability ease of sublimation
The spectral properties of such complexes are tunable by ligand functionalization, which makes them promising active layer materials for OLED devices.[25−35] Most of the azomethine’s zinc complexes described in the literature, which can be used as a source of blue electroluminescence, derive from salicylic aldehyde.[29]
Summary
Despite the significant progress achieved since the first preparation of organic light-emitting diodes (OLEDs) by Tang[1] and Burroughes,[2] the lack of cheap and processable electro-luminophores still represents immediate needs. Fully organic molecules are insufficiently stable, which shortens their durability and requires a more elegant molecular engineering solution and elaboration of protective encapsulating coatings.[18] an inexpressive band with a large half-width at a maximum of ∼200−100 nm is often seen in the luminescence spectrum of organic polymers, which does not allow them to reproduce pure colors.[19−21] Coordination compounds of platinoids demonstrate high stability and excellent brightness during exploitation in OLEDs, but given the high cost and small world reserves of Ir, Pt, and Os, the search for new cheaper sources of blue electroluminescence is still relevant In this respect, zinc Schiff base complexes with benzoheterocycles are of considerable interest, the synthesis of which has recently been intensified owing to their very intense blue photoluminescence emission.[22−24] In addition, the zinc complexes of azomethine ligands exhibit good electron transport ability, high fluorescence quantum yields, and excellent thermostability ease of sublimation. 4-acylpyrazolone derivatives have become increasingly interesting as structural and functional analogs of salicylic aldehyde and have proven to be useful for the creation of new Received: May 6, 2021 Accepted: August 4, 2021 Published: August 11, 2021
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