Two novel D–A (donor–acceptor) and one D–A–D small molecules containing mesitylborane as an acceptor and triphenylamine as a donor, linked through a thieno[3,2-b]thiophene π-conjugated spacer, are synthesized and characterized.
TPE units at the periphery of two TTs and a DTT affect the structures, properties and OLED characteristics of these three synthetically easily accessible novel conjugated compounds for materials chemistry.
Applying thienothiophenes (TT) as a linker, a bulky bifunctional thienothiophene, TT-TPA-TPE3, possessing triphenylamine (TPA) and tetraphenylethylene (TPE) units, was designed, synthesized, and fully characterized. Its optical and electronic properties were explained by UV-Vis spectroscopy, cyclic voltammetry (CV) and Aggregation-Induced Emission (AIE) study. TT-TPA-TPE3 exhibited positive solvatochromism in the range of solvent polarities from DMF to toluene, displaying emissions from yellowish to bluish between 480-525 nm. Utilizing TT-TPA-TPE3 as a hole-transporting layer, its organic light emitting devices (OLEDs) were fabricated and their performances were investigated. The synthesized emitter exhibited green and blue emissions in device applications. A mega Stoke's shift of 114 nm in THF and a large Stoke's shift of 78 nm on ITO were observed. A maximum luminance of 580 cd m À 2 and a turn-on voltage of 7.01 V were obtained, indicating that TT-TPA-TPE3 has a good hole-transporting ability.
Functionalization from nonperipheral
positions of triazatruxene
is representing a challenge. Triarylation of the nonperipheral positions
(1, 6, and 11) in triazatruxene scaffold has been achieved for the
first time via two approaches. The transformations involve arylation/cyclotrimerization
and cyclotrimerization/arylation sequences. POCl3-mediated
direct cyclotrimerization of oxindoles containing electron-deficient
substituents on the aryl group at the C7-position resulted in the
formation of 2-chloroindoles, whereas oxindoles containing electron-donating
substituents gave the triazatruxenes. Furthermore, desired triazatruxenes
were achieved through cyclotrimerization of 7-bromooxindole followed
by coupling with arylboronic acids. NMR structural analysis exhibited
that two of the suitably substituted oxindole and triazatuxene may
have atropisomerism at room temperature. As a representative triazatruxene
scaffold, the optoelectronic properties of 9a have also
been studied via ultraviolet–visible (UV–vis) absorption
spectra and fluorescence spectra of 9a thin films. Also,
density functional theory calculation was realized to get knowledge
about frontier molecular orbitals. In the light of the information
obtained, an organic light-emitting diode (OLED) device utilizing 9a as an emissive layer was applied to obtain white emission.
In brief, this study provides the first examples of the synthesis
of triazatruxenes bearing aryl substituents at the nonperipheral positions
as candidate compounds for organic electronics, optoelectronics, and
material chemistry.
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