Syntheses and characterization of carbazole based new low‐band gap copolymers containing highly soluble benzimidazole derivatives for solar cell application

Kim, Jae Hong; Park, Sung Heum; Kim, Jin-Woo; Cho, Shinuk; Jin, Youngeup; Shim, Joo Young; Shin, Hyeonsook; Kwon, Sooncheol; Kim, Il; Lee, Kwang-Hee; Heeger, Alan J.; Suh, Hongsuk

doi:10.1002/pola.24435

Cited by 23 publications

(8 citation statements)

References 23 publications

(24 reference statements)

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“…However, contrary to our expectation, the new 2-EBI , 2-BBI , and 2-HBI copolymers exhibit a negligible PCE (0.45%, 0.17%, and 0.26%), and in fact their lowest-energy absorption occurs at a much shorter wavelength (λ max ∼ 420 nm ∼ 2.95 eV) (Sections –), as also found for other copolymers with the same units in our previous studies. , This anomalous side-group effect of the 22BI-containing copolymers 2 presents a striking contrast to 2BTA-based copolymers whose favorable optical and photovoltaic properties are not compromised by long alkyl side chains in 2BTA. ,, What is more intriguing is that the absorption peak at λ max of 623 nm (1.99 eV) is restored when the long dialkyl chains are replaced by a cyclohexyl group . This cyclohexyl-analogue copolymer ( 2-cHBI ; see below in Section ) shows a slightly improved PCE (1%) . It appears that only long and flexible alkyl groups of 22BI induce unfavorable side-group effects.…”

Section: Introductioncontrasting

confidence: 77%

“…A higher tendency of reaction from a quinoid -type copolymer 2 to an aromatic copolymer 4 is expected for 2-EBI , 2-BBI , and 2-HBI than for 2-MBI and 2-cHBI . This may explain the observed side-group effect on the absorption spectra and PCE of the copolymer 2 . − …”

Section: Dft Calculations and Hypothesesmentioning

confidence: 94%

“…13,26,27 What is more intriguing is that the absorption peak at λ max of 623 nm (1.99 eV) is restored when the long dialkyl chains are replaced by a cyclohexyl group. 34 This cyclohexyl-analogue copolymer (2-cHBI; see below in Section 3) shows a slightly improved PCE (1%). 34 It appears that only long and flexible alkyl groups of 22BI induce unfavorable side-group effects.…”

Section: Introductionmentioning

confidence: 99%

“…34 This cyclohexyl-analogue copolymer (2-cHBI; see below in Section 3) shows a slightly improved PCE (1%). 34 It appears that only long and flexible alkyl groups of 22BI induce unfavorable side-group effects.…”

Section: Introductionmentioning

confidence: 99%

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Palladium-Assisted Reaction of 2,2-Dialkylbenzimidazole and Its Implication on Organic Solar Cell Performances

Song

Park

et al. 2015

J. Phys. Chem. C

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A 2,2-dimethyl-2H-benzimidazole (22MBI) pulling unit has been synthesized as a potential high-solubility substitute for benzothiadiazole and incorporated into a push−pull-type copolymer used for decent-efficiency (∼3%) organic photovoltaic devices. We herein replace the two methyl side groups of 22MBI by longer alkyl (ethyl, butyl, and hexyl) side chains to further improve the solubility. However, the copolymers replaced by the new pulling units, 2,2-diethyl/dibutyl/dihexl-2H-benzimidazole (22EBI/22BBI/22HBI), lose favorable optical characteristics and exhibit negligible (<0.5%) power conversion efficiency. Intrigued by this anomalous side-group effect of 2,2-dialkyl-2H-benzimidazole (22BI), we carry out time-dependent density functional theory calculations on a series of 22BI-based copolymers with various lengths of 2,2-dialkyl side chains (methyl, ethyl, butyl, and hexyl), but no discernible difference in equilibrium structure nor in electronic structure is found between them. We hence formulate a hypothesis that 22BI may either isomerize into 1,2-dialkylbenzimidazole (12BI) or lose one of its alkyl (≥ethyl) chains as olefin to become 2-dialkylbenzimidazole (2BI) because these aromatic products, unlike the quinoidtype 22BI, would exhibit unfavorable electronic structure for organic photovoltaic (OPV) applications. Indeed, the absorption spectra measured for the 22BI-based copolymers with long dialkyl side chains are best reproduced by the calculations on 2BI-and 12BI-based copolymers, and the two side products are calculated to be more stable than 22BI, indicating the spontaneity of the proposed reactions. The activation barriers are prohibitively high (>29 kcal/mol) but could be reduced down to 8 kcal/mol in the presence of palladium-based polymerization catalysts. Indeed, the presence of the predicted 12BI-containing side products is confirmed by NMR spectra. A temperature-dependent polymerization experiment shows that 22MBI is in fact subject to the same type of isomerization when the temperature is raised to 150°C above the original polymerization temperature (90−110°C ), further supporting the hypothesis from our calculations and explaining the observed anomalous side-group effect.

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Section: Introductioncontrasting

confidence: 77%

Section: Dft Calculations and Hypothesesmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Palladium-Assisted Reaction of 2,2-Dialkylbenzimidazole and Its Implication on Organic Solar Cell Performances

Song

Park

et al. 2015

J. Phys. Chem. C

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“…The synthetic procedure of the target QI-based molecules is illustrated in Scheme 2 and Fig S1. † To prepare the key intermediates 5a-d, diisopropyl 2,3-dioxosuccinate 34 was condensed with the corresponding dibromobenzene-diamine derivatives. [35][36][37][38] The carboxylic acid compounds 6a-d were obtained by hydrolysis with sodium hydroxide and successive hydrochloric acid treatment. Subsequently, 6a-d were treated with acetyl chloride to provide anhydrides 7a-d.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

Fluorination and chlorination effects on quinoxalineimides as an electron-deficient building block for n-channel organic semiconductors

et al. 2019

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Red/NIR‐Emissive Benzo[d]imidazole‐Cored AIEgens: Facile Molecular Design for Wavelength Extending and In Vivo Tumor Metabolic Imaging

et al. 2018

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biological imaging, [3] owing to their deep tissue penetration, less biological photodamage, and minimum interference from background autofluorescence of biomolecules in living systems. [4] To date, this is still of great demand to develop new long-wavelength emissive fluorophores. Lengthening the π-electron system has been recognized as one of the general design strategy to develop fluorescent materials with long wavelength absorbing or emitting, for example, oligo-olefins and polymethine dyes. [4a,5] However, these conventional fluorophores possess thermal and photochemical instability, small Stokes shift, high interference from the excitation light and/or self-absorption, and aggregation-caused quenching (ACQ) effect (strong emission in dilute solution but quenching upon the concentration increased due to their strong intermolecular π-π interactions). All these respective and collective drawbacks limit their biomedical applications. [6] The donor-acceptor (D-A) architecture has been a broadly adopted strategy for designing the long-wavelength emissive molecules, [7] whereby electron-donating and electron-withdrawing segments are incorporated into the molecular backbone. [8] After the molecular orbitals (MOs) of the conjugated Aggregation-induced emission (AIE) luminogens (AIEgens) with red/nearinfrared (NIR) emissions are appealing for applications in optoelectronics and biomedical engineering owing to their intrinsic advantages of efficient solidstate emission, low background, and deep tissue penetration. In this context, an AIEgen with long-wavelength emission is synthesized by introducing tetraphenylethene (TPE) to the periphery of electron-deficient spiro-benzo[d] imidazole-2,1′-cyclohexane (BI). The resulting AIEgen, abbreviated as 2TPE-BI, adopts a donor-acceptor structure and shows bathochromic absorption and emission with a larger Stokes shift of 157 nm in acetonitrile than that based on benzo[c][1,2,5]thiadiazole. It also exhibits a high solid-state fluorescence quantum yield of 56.6%. By further insertion of thiophene to its molecular structure generates 2TPE-2T-BI with higher conjugation and NIR emission. 2TPE-2T-BI can be fabricated into AIE dots for in vivo metabolic labeling through bio-orthogonal click chemistry. These results open a new approach for facile construction of long-wavelength emissive AIEgens based on the BI core.Molecular construction of organic π-conjugated materials owning long-wavelength emissive properties has been of great demand and potential applications in the photoelectronic devices, such as organic light-emitting diodes [1] and luminescent solar concentrator. [2] More importantly, long-wavelength emissive fluorescent materials have many prominent merits in Scheme 1. Design strategy of quinoidal AIEgens based on benzo[d]imidazole acceptor and antistacking spiro-cyclohexane substituent.

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Syntheses and characterization of carbazole based new low‐band gap copolymers containing highly soluble benzimidazole derivatives for solar cell application

Cited by 23 publications

References 23 publications

Palladium-Assisted Reaction of 2,2-Dialkylbenzimidazole and Its Implication on Organic Solar Cell Performances

Palladium-Assisted Reaction of 2,2-Dialkylbenzimidazole and Its Implication on Organic Solar Cell Performances

Fluorination and chlorination effects on quinoxalineimides as an electron-deficient building block for n-channel organic semiconductors

Red/NIR‐Emissive Benzo[d]imidazole‐Cored AIEgens: Facile Molecular Design for Wavelength Extending and In Vivo Tumor Metabolic Imaging

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