New Boron(III) Blue Emitters for All‐Solution Processed OLEDs: Molecular Design Assisted by Theoretical Modeling

Abstract

Luminescent boron(III) complexes have recently been employed as emitters in organic light‐emitting diodes (OLEDs) with reasonable success. They are easy to prepare and sufficiently stable to be used in such devices, being of great interest as a simple molecular emissive layer. Although emitters for this class with all colors have already been reported, highly efficient and stable blue emitters for applications in solution processed devices still pose a challenge. Here, we report the design, synthesis, and characterization of new boron complexes based on the 2‐(benzothiazol‐2‐yl)phenol ligand (HBT), with different donor and acceptor groups responsible for modulating the emission properties, from blue to red. The molecular design was assisted by calculations using our newly developed formalism, where we demonstrate that the absorption and fluorescence spectra can be successfully predicted, which is a powerful technique to evaluate molecular photophysical properties prior to synthesis. In addition, density functional theory (DFT) enables us to understand the molecular and electronic structure of the molecules in greater detail. The molecules studied here presented fluorescence efficiencies as high as Φ = 0.88 and all solution processed OLEDs were prepared and characterized under an ambient atmosphere, after dispersion in the emitting layer. Surprisingly, even considering these rather simple experimental conditions, the blue emitters displayed superior properties compared to those in the present literature, in particular with respect to the stability of the current efficiency.

Accurate Computation of the Absorption Spectrum of Chlorophyll a with Pair Natural Orbital Coupled Cluster Methods

“…This approach essentially amounts to calculating Fermi’s golden rule by Fourier transforming it into the time domain and applying the path integral formula for the harmonic oscillator to evaluate the resulting time-correlation function. The resulting composite method has been used with success to characterize and interpret a variety of spectroscopic measurements. − ,− It is also worthwhile to mention a similar approach used by Barone and co-workers on a variety of chemical compounds. − …”

Synthesis of a Boronic Acid Anhydride Based Ligand and Its Application in Beryllium Coordination

“…The latter signal is in the typical range of three-coordinate boron nuclei and this is also supported by the broad linewidth of 415 Hz. [34] Related threecoordinate phenylboronic acid and phenylboroxine also exhibit broad 11 B NMR signals around 30 ppm [35] and derivatized boronic acids are observed from 26.9 to 32.0 ppm. [36] The signal at 8.4 ppm with a linewidth of 113 Hz is typical for a four-coordinate boron nucleus [34] and related 2,6-dimethanolpyridine arylboronic acid esters show chemical shifts of 8.0-8.4 ppm.…”

“…[1][2][3][4][5] With the help of O,O-chelating ligands, devices with an emission in the red/near-infrared were realized, [6] while C,N-chelated boron yields blue-green to red, [7,8] and N,O-chelation yields blue emission respectively. [9][10][11][12] While at the beryllium center. Incorporation of a beryllium atom in a six-membered ring causes no more distortion than the corresponding boron atom, suggesting that analogous ligand systems could be used in boron and beryllium coordination chemistry.…”

“…Over the last decade boron‐based dyes for OLEDs have gained much attention and through the use of N , N ‐chelating ligands, devices could be constructed which – depending on the ligand design – emit within the near‐UV to the orange region . With the help of O , O ‐chelating ligands, devices with an emission in the red/near‐infrared were realized, while C , N ‐chelated boron yields blue‐green to red,, and N , O ‐chelation yields blue emission respectively . While an abundance of boron compounds have been investigated as potential components of OLED devices, the number of related beryllium compounds is extremely limited, even though these compounds show promise in the construction of white emitting OLEDs .…”

Enhanced Performance of All‐Solution Processed Multilayer OLEDs by Photoluminescence Lifetime Reduction of Cu(I) Complex Emitters Containing Chalcogenolate‐Diimine Ligands

“…Initially, the device structure was systematically varied and improved to obtain an optimized OLED performance. C2 was used as emitter due to its relatively high photoluminescence quantum yield (PLQY) and dispersed in two different hosts, TcTA (μ h = 2 × 10 À 5 cm 2 V À 1 s À 1 ; T 1 = 2.78 eV) and OXD: 7 (μ e = 4 × 10 À 5 cm 2 V À 1 s À 1 ; T 1 = 2.72 eV), [19,20] chosen due to their high triplet energy (T 1 ) to facilitate the exciton confinement on the emitter, and their good charge carrier mobility (μ h and μ e ) and excellent thin film formation. [21] 3) to evaluate the electron injection effects on the OLED performance.…”