Luminescence of Pyrazinyl Pyrazolate Pt(II) Complexes Fine-Tuned by the Solid-State Stacking Interaction
Journal
Energy and Fuels
Journal Volume
35
Journal Issue
23
Pages
19112-19122
Date Issued
2021
Author(s)
Abstract
Three functional pyrazinyl pyrazolate Pt(II) complexes [Pt(fprpz)2] (1), [Pt(2fprpz)2] (2), and [Pt(5fprpz)2] (3), each with CF3, CF2H, and C2F5 substituents on pyrazolate, were synthesized from treatment of Pt(DMSO)2Cl2 and respective pyrazinyl pyrazole chelates (fprpz)H, (2fprpz)H, and (5fprpz)H in refluxing tetrahydrofuran solution. Variations of these fluorinated substituents provided a profound effect on both the photo- and electroluminescence properties of as-prepared Pt(II) metal complexes in solution and solid states, respectively. More specifically, there exists a dominant ligand-centered 3ππ∗ state contribution in both the solution state and doped thin films at a low concentration, which are strongly dependent upon the nature of the pyrazolate entity and tendency of self-aggregation. A systematic study demonstrates that the T1 state properties can be fine-tuned by altering their functional substituents. Because Pt(II) complex 2 bears the least electron-deficient CF2H substituent, its thin film has shown the longest emissive wavelength in comparison to other derivatives. Upon formation of a vacuum-deposited thin film, the transition of the titled Pt(II) complexes is dominated by metal-metal-to-ligand charge transfer transition that can be tuned by the well-aligned stacking of the Pt(II) complexes, being more delocalized hence decreasing the energy upon increasing the stacking density. Moreover, we fabricated a series of organic light-emitting diodes (OLEDs) in an attempt to probe the concentration dependence of the doped emitter versus device performances. The electroluminescence of Pt(II) complex 1 shifted from sky blue to near infrared as the doping ratio gradually increased from 1 to 100 wt %. Broad-band white emission can also be realized by adjusting the concentration for optimal monomeric and aggregate emissions. With this remarkable feature, a highly efficient white OLED with external quantum efficiency up to 21.4% and spectral coverage from 450 to 800 nm was obtained at the doping level of 10 wt %, representing ideal candidates in developing solid-state lighting luminaries. © 2021 American Chemical Society.
SDGs
Other Subjects
Charge transfer; Dimethyl sulfoxide; Electroluminescence; Infrared devices; Ligands; Light; Metal complexes; Organic light emitting diodes (OLED); Organic solvents; Platinum metals; Quantum theory; Semiconductor doping; Synthesis (chemical); Thin films; Concentration dependence; Electroluminescence properties; External quantum efficiency; Fluorinated substituents; Functional substituent; Metal to ligand charge transfers; Organic light emitting diodes(OLEDs); Tetrahydrofuran solution; Platinum compounds
Type
journal article