Dioxaborin Compounds with Terminal Carbazole Groups: Enhancing Electron Acceptor in Organic Photovoltaics
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Abstract Three donor−acceptor−donor dioxaborin compounds containing carbazoles as the terminal electron donor groups were synthesized. Their electronic and photovoltaic properties were compared with those of an analog with terminal triphenylamine groups. The HOMO and LUMO levels of the N ‐phenylcarbazole derivative were 0.3 and 0.1 eV lower, respectively, than those of the triphenylamine analog. During the evaluation of organic photovoltaic characteristics, the N ‐phenylcarbazole derivative exhibited a power conversion efficiency (PCE) of 2.06 % when combined with a conducting polymer (PTB7‐Th). Contrarily, the triphenylamine analog exhibited a PCE of 2.85 % when combined with a fullerene acceptor (PC 61 BM). The results showed that the N ‐phenylcarbazole and triphenylamine derivatives functioned as electron acceptor and donor materials, respectively. The conversion from the electron donor to the acceptor was achieved via a slight change in the structure of the terminal donor groups of the dioxaborin compounds. This study will prove valuable for the development of nonfullerene acceptors.Keywords:
Triphenylamine
Acceptor
Carbazole
Electron acceptor
Electron donor
HOMO/LUMO
Triphenylamine
Carbazole
Quantum yield
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Triphenylamine
Carbazole
Thermal Stability
HOMO/LUMO
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Carbazole
Triphenylamine
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Three new carbazole copolymers, poly(9-(2,5-diarene-[1,3,4]oxadiazole)-carbazole-alt-9-(2-ethylhexyl)-carbazole-3,6-diyl)s (P1), poly(9-(2,5-diarene-[1,3,4]oxadiazole)-2, 7-carbazole-alt-9-(2-ethylhexyl)-3, 6-carbazole-diyl)s (P2), and poly(9-(2,5-diarene-[1,3,4]oxadiazole)-carbazole-alt-9-(2-ethylhexyl)-carbazole-2,7-diyl)s (P3), were synthesized by the Suzuki coupling reaction. The copolymers were characterized by 1H NMR, 13C NMR, and elements analysis, and their molecular weights were estimated using gel permeation chromatography. The TGA and DSC results revealed their good thermal stability with high glass-transition temperatures (Tg) at 211 °C (P1), 194 °C (P2), and 208 °C (P3), respectively. The copolymers exhibited blue emission with significantly improved fluorescence quantum efficiencies compared to their analogous polymers. The triplet energies of P1, P2, and P3 were determined to be 2.52, 2.42, and 2.32 eV, respectively, from their phosphorescent spectra at 77 K. The HOMO/LUMO levels of the carbazole copolymers can be tuned by different coupling positions and substitution at the 9-position of carbazole. P1 by connecting carbazole units via their 3 (6) positions shifts the HOMO/LUMO levels to higher energy compared to P2 via 2 (7) positions, whereas replacing alkyl groups at the 9-position of carbazole with electron-withdrawing diaryl-1,3,4-oxadiazole group shifts the HOMO/LUMO levels to lower energy. Finally, polymer light-emitting diodes employing the P1−3 as host and bis(2,4-diphenylquinolinato-N,C2′)iridium(acetylacetonate) (Ir(ppq)2(acac)) as guest were constructed and characterized electrically.
Carbazole
HOMO/LUMO
Oxadiazole
Thermal Stability
Proton NMR
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New organic materials containing a cyano‐functionalized carbazole moiety at one end linked to different chromophores such as fluorene, carbazole, and triphenylamine at the other end through an acetylene spacer are synthesized and characterized by photophysical, electrochemical, thermal, and electroluminescence studies. A meta ‐like linkage at the C‐2 and C‐7 atoms of the central carbazole moiety and the choice of chromophore restricted the emission to the near‐ultraviolet region. The photophysical properties of the compounds depend on the nature of the chromophore attached to the carbazole unit. A triphenylamine‐substituted derivative exhibited the longest wavelength emission in the series, attributable to the elongated conjugation and electron richness of triphenylamine, whereas the phenyl‐ and fluorene‐functionalized molecules showed the shortest wavelength emissions with vibronic patterns. The compounds containing carbazole and triphenylamine units exhibited positive solvatochromism in their fluorescence spectra, and this behavior is characteristic of charge transfer from a donor to an acceptor. A fluorene derivative containing cyano substituents at the carbazole and fluorene moieties exhibited the best electroluminescence characteristics in the series, probably because of balanced charge transport and effective confinement of the excitons in the emissive layer.
Triphenylamine
Carbazole
Chromophore
Moiety
Solvatochromism
Acceptor
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The 2,7- and 3,6-substituted carbazole and triphenylamine chalcogenophene (Se, Te) derivatives and their electrodeposited polymers are investigated using electrochemical and UV–vis–NIR/ESR spectroelectrochemical methods. Major differences in the case of oxidation and electropolymerization behavior between monomers and related polymers are shown. Se and Te atoms do not conjugate their lone electron pairs with the π-conjugated system and therefore only increase the contribution of the quinoid form of the chalcogenophene unit. The 2,7- substituted carbazole derivatives present stronger carbazole–chalcogenophene conjugation than 3,6-substituted derivatives. One 3,6-substituted carbazole derivative and triphenylamine derived polymers were found to have promising electrochromic properties with black electrochromism.
Triphenylamine
Carbazole
Lone pair
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Triphenylamine
Moiety
Electron donor
Acceptor
Electron acceptor
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Carbazole-based diamines, E-Cz or K-Cz, were unexpectedly synthesized via the hydrogenation reaction in one pot, where the reduction of the nitro group, the deprotection of the benzyl group, and the coupling of triphenylamine happen simultaneously.
Carbazole
Triphenylamine
Coupling reaction
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Electron donor
Electron acceptor
Acceptor
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Triphenylamine
Carbazole
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