Amphoteric Redox Research Articles

ProDOT-Assisted Isomerically Pure Indophenines.

Reactions between 3,4-propylenedioxythiophenes (ProDOTs) and N-alkyl isatins under ambient conditions result in isomerically pure indophenine materials as confirmed by TLC and 1H NMR analysis. The resulting low band gap materials exhibit favorable inter- and intramolecular interactions, high thermal stabilities, low energy electronic transitions, and amphoteric redox behavior.

Dicyclopenta[4,3,2,1- ghi:4',3',2',1'- pqr]perylene: A Bowl-Shaped Fragment of Fullerene C70 with Global Antiaromaticity.

Solution-phase synthesis of buckybowls remains a big challenge, and there are limited reports on the fragments of C70. Herein, we report a new basic subunit of C70 with C2v symmetry, the dicyclopenta[4,3,2,1- ghi:4',3',2',1'- pqr]perylene (2CP-Per). Its aryl-substituted derivative 2CP-Per-Ar was synthesized and shows a bowl-shaped geometry according to X-ray crystallographic analysis. A fast bowl-to-bowl inversion process was observed above 183 K by variable temperature nuclear magnetic resonance (NMR), with a small inversion energy barrier. 2CP-Per-Ar displays amphoteric redox behavior with a small electrochemical energy gap (1.29 eV). Different from many other aromatic buckybowls, 2CP-Per exhibits global antiaromaticity with a strong paratropic ring current associated with the 16π-electrons rim, as revealed by NMR measurements and theoretic calculations. Its dianion is aromatic, similar to its isoelectronic structure coronene. Its dication is predicted to be aromatic, with a [6]annulene-within-[14]annulene structure.

Bowl-Shaped Carbon Nanobelts Showing Size-Dependent Properties and Selective Encapsulation of C70.

The synthesis of carbon nanobelts (CNBs) with well-defined size and structure remains a challenging topic in nanocarbon chemistry and materials science. Herein, we report the synthesis, physical characterization, and supramolecular properties of two fully conjugated bowl-shaped CNBs (CNB1/CNB2), in which six/eight cyclopenta-rings are fused onto a macrocycle containing three/four alternately linked 2,7-pyrenyl and 2,7-phenanthryl units. The existence of five-membered rings results in a bowl-shaped geometry, as revealed by X-ray crystallographic analysis and density functional theory calculations. Both molecules contain an alternate aromatic phenanthrene- co-quinoidal pyrene structure to satisfy Clar's aromatic sextet rule. The smaller size CNB1 has a deeper bowl depth ( d = 4.997 Å) than CNB2 ( d = 3.682 Å) and cannot undergo bowl-to-bowl (BTB) inversion below 373 K in toluene. However, the larger size CNB2 shows a smaller BTB inversion barrier (∼12 kcal/mol) at the coalescent temperature (248 K), which was estimated by variable-temperature NMR measurements. Both compounds exhibit a small energy gap and amphoteric redox behavior with multiple redox waves. The dications of CBN1 and CBN2, and the tetracation of CBN2, are experimentally accessible by chemical oxidation with NO·SbF6, all displaying unusual open-shell singlet diradical character with a small singlet-triplet energy gap (Δ ES-T = -2.71 kcal/mol for CBN12+, -2.50 kcal/mol for CBN22+, and -2.00 kcal/mol for CBN24+). The dications are globally aromatic while the tetracations are globally antiaromatic according to NMR measurements and theoretical calculations (anisotropy of the induced current density, nucleus independent chemical shift, and 2D isochemical shielding surface). The small bowl-shaped CNB1 demonstrates selective encapsulation of fullerene C70 over C60, with a large association constant ( Ka = 8.066 × 105 M-1 in toluene). However, the larger size CNB2 does not exhibit any encapsulation with both C60 and C70.

Synthesis and photophysical properties of azuleno[1′,2′:4,5]pyrrolo[2,1-b]quinazoline-6,14-diones: Azulene analogs of tryptanthrin

Azulene analog of tryptanthrin, azuleno[1′,2′:4,5]pyrrolo[2,1-b]quinazoline-6,14-dione, was successfully prepared by the condensation reaction of azuleno[2,1-b]pyrrole-2,3-dione with isatoic anhydride in the presence of sodium hydride or diisopropylethylamine (DIPEA). Its 2-halo derivatives were also obtained in high yields by the condensation reaction with 5-haloisatoic anhydrides in the presence of DIPEA. Reactivity toward electrophilic reagents was revealed by halogenation with N-bromosuccinimide (NBS) or N-iodosuccinimide (NIS) to afford 12-halo derivatives in high yields. Among the halo derivatives, 2-iodo and 12-iodo derivatives were reactive enough to afford phenylethynyl derivatives under Pd-catalyzed Sonogashira cross-coupling conditions. Within the phenylethynyl derivatives, only 12-phenylethynyl derivative was transformed into its 1,1,4,4-tetracyanobutadiene (TCBD) derivative by the reaction with TCNE. Amphoteric redox properties of the novel azulene analogs of tryptanthrin were characterized by spectroscopic and voltammetric analyses.

Anthracene‐Fused Dibenzo[def,mno]chrysenes with a Helical Structure

AbstractScholl‐type oxidative cyclodehydrogenation reactions were conducted for an anthryl‐substituted dibenzo[def,mno]chrysene (DBC) precursor with the intention to prepare anthracene‐fused DBCs with extended conjugation. The compound ADBC‐1 with one cyclized ring and its two chloro‐ and oxy‐ derivatives (ADBC‐Cl and ADBC‐O) with good stability were successfully isolated and characterized. They showed largely red‐shifted absorption spectra and amphoteric redox behavior. XRD analysis revealed that they can be regarded as large polycyclic aromatic hydrocarbons (PAHs) containing [5]helicene substructures with large twist angles of 67.8°–73.7° owing to steric congestion. Further cyclization to form newer C−C bonds failed, which can be explained by an open‐shell diradical character and high HOMO energy levels of the products according to spin‐unrestricted DFT calculations.

Construction of Polycyclic π-Conjugated Systems Incorporating an Azulene Unit Following the Oxidation of 1,8-Diphenyl-9,10-bis(phenylethynyl)phenanthrene.

Polycyclic aromatic hydrocarbons (PAHs) that incorporate either heptagons or pentagons consist of non-planar molecular structures with unusual optoelectronic properties, and the design of a relatively simple and efficient method to construct these highly fused π-conjugated systems with odd-membered rings is in high demand. This work describes the use of silver(I) cations to promote the efficient synthesis of azulene-embedded PAH 2, which is a structural isomer of tribenzo[fg,ij,rst]pentaphene 3, via tandem oxidative transannulation between the phenyl and arylethynyl moieties. This method involves a carbophilic interaction of the silver(I) cation with the acetylene units, which facilitates an electron transfer in the initial step. The synthesized PAH 2 and the protonated cation 2 H⋅BF4 were fully characterized by X-ray crystallographic analysis, electronic absorption, electrochemical measurement, and quantum chemical calculation. The azulene-embedded PAH 2 exhibited a low-energy absorption band and amphoteric redox events, which were characterized as non-alternant characteristics originating from the azulene unit.

π-Conjugated Polymers Incorporating a Novel Planar Quinoid Building Block with Extended Delocalization and High Charge Carrier Mobility.

Two novel conjugated polymers incorporating quinoidal thiophene are successfully synthesized. By combining 1D nuclear magnetic resonance (NMR) and 2D nuclear Overhauser effect spectroscopy analyses, the isomeric form of the major quinoid monomer is clearly identified as the asymmetric Z, E-configuration. The quinoidal polymers are synthesized via Stille polymerization with thiophene or bithiophene. Both quinoidal polymers exhibit the low band gap of 1.45 eV and amphoteric redox behavior, indicating extended conjugation owing to the quinoidal backbone. These quinoidal polymers show ambipolar behaviors with high charge carrier mobilities when applied in organic field-effect transistors. In addition, the radial alignment of polymer chains achieved by off-center spin-coating leads to further improvement of device performance, with poly(quinoidal thiophene-bithiophene) exhibiting a high hole mobility of 8.09 cm2 V-1 s-1 , which is the highest value among the quinoidal polymers up to now. Microstructural alteration via thermal annealing or off-center spin-coating is found to beneficially affect charge transport. The enhancement of crystallinity with strong π-π interactions and the nanofibrillar structure arising from planar well-delocalized quinoid units is considered to be responsible for the high charge carrier mobility.

Conducting nanofibres of solvatofluorochromic cyclohexanetrione-dithiolylidene-based C3 symmetric molecule.

We report a novel set of easily tailorable C3 symmetric molecules with a π-extended core and adorned with different thioalkyl groups, exhibiting solvatofluorochromic and amphoteric redox behaviour. The nearly planar core exhibits intermolecular face-to-face π-stacking, SS and intramolecular SO interactions. Current-sensing atomic force microscopy studies revealed a high conductivity of ∼0.15 mS cm-1 in the undoped J-aggregate nanofibres of the thiopropyl appended gelator.

1,4-Dihydropyrrolo[3,2-b]pyrroles as a Single Component Photoactive Layer: A New Paradigm for Broadband Detection.

Single component organic photodetectors capable of broadband light sensing represent a paradigm shift for designing flexible and inexpensive optoelectronic devices. The present study demonstrates the application of a new quadrupolar 1,4-dihydropyrrolo[3,2-b]pyrrole derivative with spectral sensitivity across 350-830 nm as a potential broadband organic photodetector (OPD) material. The amphoteric redox characteristics evinced from the electrochemical studies are exploited to conceptualize a single component OPD with ITO and Al as active electrodes. The photodiode showed impressive broadband photoresponse to monochromatic light sources of 365, 470, 525, 589, 623, and 830 nm. Current density-voltage (J-V) and transient photoresponse studies showed stable and reproducible performance under continuous on/off modulations. The devices operating in reverse bias at 6 V displayed broad spectral responsivity (R) and very good detectivity (D*) peaking a maximum 0.9 mA W-1 and 1.9 × 1010 Jones (at 623 nm and 500 μW cm-2) with a fast rise and decay times of 75 and 140 ms, respectively. Low dark current densities ranging from 1.8 × 10-10 Acm-2 at 1 V to 7.2 × 10-9 A cm-2 at 6 V renders an operating range to amplify the photocurrent signal, spectral responsivity, and detectivity. Interestingly, the fabricated OPDs display a self-operational mode which is rarely reported for single component organic systems.

Low-Dimensional Carbon Allotropes: Ground- and Excited-State Charge Transfer with NIR-Absorbing Heptamethine Cyanine

Summary At the focal point of our studies are mutual interactions between an anionic heptamethine cyanine and individualized single-walled carbon nanotubes (SWCNTs) or exfoliated nanographene (NG). Here, we report the distinct near-infrared absorption of the heptamethine cyanine, which assists in visualizing the electronic interactions in the ground state with ease and precision. In statistical Raman assays, we conclude from downshifted 2D- and G-modes for SWCNTs, as well as upshifted 2D- and downshifted G-modes for NG, that these electronic interactions result in stable n-doping of SWCNTs and NG. Key to this shift of charge density is the electron-donating character of the heptamethine cyanine. In the excited state, a complete but metastable transfer of charges is accompanied by a radical-ion-pair state that lives for several nanoseconds. Such a time domain has not yet been realized, for example, in NG to date.

A Stable N-Annulated Perylene-Bridged Bisphenoxyl Diradicaloid and the Corresponding Boron Trifluoride Complex.

Organic π-extended radicals display unique electronic structures, and could be used as promising functional materials. However, design and synthesis of stable radicals are challenging for chemists due to their high reactivity. In this work, we synthesized a stable N-annulated perylene-bridged bisphenoxyl diradicaloid, and its complex with Lewis acid boron trifluoride. Their ground-state geometric and electronic structures were systematically studied by various experimental methods, including X-ray crystallographic analysis, variable-temperature NMR spectroscopy, electron-spin resonance spectroscopy (ESR), and superconducting quantum interference device (SQUID) measurements, supported by density functional theory. Both were observed as open-shell singlet diradicaloids in the ground state. The bisphenoxyl diradicaloid demonstrated string features of strong near-infrared (NIR) absorption, closely packed π-dimer structure in crystals, amphoteric redox behavior with a small HOMO-LUMO energy band gap, and a rather small singlet-triplet gap, whereas the complex showed very different photophysical, electrochemical, and magnetic properties. Our studies provide an efficient method of making stable diradicaloids by Lewis acid/base complexation.

Push–Pull‐Type Polychlorotriphenylmethyl Radicals: New Two‐Photon Absorbers and Dyes for Generation of Photo‐Charges

Tri(4-iodo-2,3,5,6-tetrachlorophenyl)methane (2) is reported as a general building block for the synthesis of various π-conjugated polychlorotriphenylmethyl (PTM) radicals. Three push-pull-type triphenylamine-substituted PTM radicals with different substitution patterns were prepared and all exhibited intense inter-valence charge-transfer bands and large two-photon absorption (TPA) cross sections. Moreover, increase of solvent polarity also resulted in improved TPA response. The charge-transfer character of the relevant excited states provoked the efficient photo-generation of charges, anions in the PTM and cations in the amine arms, driven by the amphoteric redox character and the small coupling between donor and acceptor.

Synthesis and properties of furan/thiophene substituted difluoroboron β-diketonate derivatives bearing a triphenylamine moiety

Two novel triphenylamine-modified difluoroboron β-diketonate derivatives containing either a furan or thiophene unit (2c and 2d) have been designed, synthesized and fully characterized. The effects of the triphenylamine substituent and different electron-rich heterocycle units (2-furyl and 2-thienyl) on the photoluminescence and electrochemical properties of these new BF2 complexes were investigated systematically. The two complexes bearing an electron-donating triphenylamine moiety showed broad absorption and intense emission bands in toluene with high fluorescence quantum yields. Significantly larger Stokes shifts were observed for these complexes in comparison to those of the corresponding reference complexes (2a and 2b). Cyclic voltammetry measurements revealed the amphoteric redox properties of the two new BF2 complexes. The results indicated that the introduction of a triphenylamine substituent into BF2 complex could result in large differences in their properties. However, making a contrast between 2c and 2d, it is found that replacing furan with thiophene in the BF2 complex showed slight effects on optical and electrochemical properties. The results of DFT calculations supported the structural and spectroscopic data and confirmed the compositions of frontier molecular orbitals in the BF2 complexes.

Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene.

Higher order acenes (i.e., acenes longer than pentacene) and extended zethrenes (i.e., zethrenes longer than zethrene) are theoretically predicted to have an open-shell singlet ground state, and the radical character is supposed to increase with extension of molecular size. The increasing radical character makes the synthesis of long zethrenes and acenes very challenging, and so far, the longest reported zethrene and acene derivatives are octazethrene and nonacene, respectively. In addition, there is a lack of fundamental understanding of the differences between these two closely related open-shell singlet systems. In this work, we report the first synthesis of a challenging nonazethrene derivative, HR-NZ, and its full structural and physical characterizations including variable temperature NMR, ESR, SQUID, UV-vis-NIR absorption and electrochemical measurements. Compound HR-NZ has an open-shell singlet ground state with a moderate diradical character (y0 = 0.48 based on UCAM-B3LYP calculation) and a small singlet-triplet gap (ΔES-T = -5.2 kcal/mol based on SQUID data), thus showing magnetic activity at room temperature. It also shows amphoteric redox behavior, with a small electrochemical energy gap (1.33 eV). Its electronic structure and physical properties are compared with those of Anthony's nonacene derivative JA-NA and other zethrene derivatives. A more general comparison between higher order acenes and extended zethrenes was also conducted on the basis of ab initio electronic structure calculations, and it was found that zethrenes and acenes have very different spatial localization of the unpaired electrons. As a result, a faster decrease of singlet-triplet energy gap and a faster increase of radical character with increase of the number of benzenoid rings were observed in zethrene series. Our studies reveal that spatial localization of the frontier molecular orbitals play a very important role on the nature of radical character as well as the excitation energy.

Quadrupolar (A-π-D-π-A) Tetra-aryl 1,4-Dihydropyrrolo[3,2-b]pyrroles as Single Molecular Resistive Memory Devices: Substituent Triggered Amphoteric Redox Performance and Electrical Bistability

A series of quadrupolar (A-π-D-π-A) tetra-aryl 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) derivatives synthesized are showcased as potential organic resistive memory (ORM) devices for the first time. The experimental observations coupled with density functional theory (DFT) calculations probe in detail the role of terminal substituent groups (p-NH2, p-Cl, p-CN, p-NO2, m-NO2) on the optical and electrical properties. Electrochemical studies reveal that the 3- and 4-dinitro derivatives form an unusual class of tetra-aryl DHPPs that exhibit intrinsic amphoteric redox behavior contrary to the literature reports. The bipolar nature within a single molecule was harnessed to design operational ORMs. Interestingly, the memory devices fabricated using the structural isomers exhibited dissimilar memory characteristics. While the p-NO2 derivative displays permanent Write Once Read Many times (WORM) memory, its meta-counterpart represents a behavior akin to rewriteable flash memory. The noticeably higher ON/OFF ratio (∼...

2,11-Dibromo-13,14-dimesityl-5,8-dioxapentaphene: A Stable and Twisted Polycyclic System Containing the o-Quinodimethane Skeleton.

A stable o-quinodimethane (oQDM) derivative, 2,11-dibromo-13,14-dimesityl-5,8-dioxapentaphene (3) was synthesized, and its structure and properties were investigated. The X-ray structural analysis showed a significantly twisted π-framework and a clear bond-length alternation in the central oQDM skeleton. Owing to the quinoidal conjugation, 3 exhibited a broad absorption band in the visible region (up to 700 nm) and amphoteric redox behavior. Furthermore, radical cation 3(•+) was isolated, and its electronic structure was elucidated by spectroscopic measurements.

Multifaceted Regioregular Oligo(thieno[3,4-b]thiophene)s Enabled by Tunable Quinoidization and Reduced Energy Band Gap.

Thiophene-based materials have occupied a crucial position in the development of organic electronics. However, the energy band gaps of oligo- and polythiophenes are difficult to modulate without resorting to push-pull electronic effects. We describe herein a new series of monodisperse oligo(thieno[3,4-b]thiophene) derivatives with well-defined regioregular structures synthesized efficiently by direct C-H arylation. These compounds show a unique palette of colors and amphoteric redox properties with widely tunable energy band gaps. The capacity to stabilize both cations and anions results in both anodic and cathodic electrochromism. Under excitation, these compounds can produce photoionized states able to interconvert into neutral triplet or form these through singlet exciton fission or intersystem crossing. These features arise from a progressive increase in quinoidization on a fully planar platform making the largest effective conjugation length among hetero-oligomers. Oligo(thieno[3,4-b]thiophene)s might represent the more distinctive family of oligothiophenes of this decade.

ChemInform Abstract: Phenalenyl‐Based Open‐Shell Polycyclic Aromatic Hydrocarbons

AbstractReview: [67 refs.

Quinoidal Molecules as a New Class of Ambipolar Semiconductor Originating from Amphoteric Redox Behavior

The two small molecules, quinoidal bithiophene (QBT) and quinoidal biselenophene (QBS), are designed based on a quinoid structure, and synthesized via a facile synthetic route. These quinoidal molecules have a reduced band gap and an amphoteric redox behavior, which is caused by an extended delocalization. Due to such properties, organic field‐effect transistors based on QBT and QBS have shown balanced ambipolar characteristics. After thermal annealing, the performances of the devices are enhanced by an increase in crystallinity. The field‐effect hole and electron mobilities are measured to be 0.031 cm2 V−1 s−1 and 0.005 cm2 V−1 s−1 for QBT, and 0.055 cm2 V−1 s−1 and 0.021 cm2 V−1 s−1 for QBS, respectively. In addition, we investigate the effect of chalcogen atoms (S and Se) on the molecular properties. The optical, electrochemical properties and electronic structures are mainly dominated by the quinoidal structure, whereas molecular properties are scarcely affected by either type of chalcogen atom. The main effect of the chalcogen atoms is ascribed to the difference of crystallinity. Due to a strong intermolecular interaction of the selenophene, QBS exhibits a higher degree of crystallinity, which leads to an enhancement of both hole and electron mobilities. Consequently, these types of quinoidal molecules are found to be promising for use as ambipolar semiconductors.

Thienoacene-fused pentalenes: syntheses, structures, physical properties and applications for organic field-effect transistors.

Three soluble and stable thienoacene-fused pentalene derivatives (1-3) with different π-conjugation lengths were synthesized. X-ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field-effect transistors (OFETs) were also investigated. The highest field-effect hole mobility of 0.016, 0.036 and 0.001 cm(2) V(-1) s(-1) was achieved for solution-processed thin films of 1-3, respectively.