Thiophene-functionalized isoindigo dyes bearing electron donor substituents with absorptions approaching the near infrared region

A series of six new, highly soluble N,N'-dialkylated isoindigo derivatives bearing different electron donating thiophene units at the 6,6'-positions were synthesized by Stille cross-coupling reaction. The optical and electrochemical properties of these dyes were studied by UV-vis spectroscopy and cyclic voltammetry, revealing a good tunability of their electronic properties by peripheral substituents with amino groups leading to strong absorption reaching the NIR region. The DFT calculations of the frontier molecular orbitals of these dyes corroborate the observed substituent effect on absorption and redox properties.     

Modulating the Properties of Azulene‐containing Polymers Through Functionalization at the 2‐Position of Azulene

Poly(2‐arylazulene‐alt‐fluorene) and poly(2‐arylazulene‐alt‐thiophene) are synthesized via Suzuki and Stille cross‐coupling polymerization, respectively, using 1,3‐dibromo‐2‐arylazulenes as monomers, which are prepared by a novel directed C?H activation method of 2‐carboxylic azulene and subsequent bromination reaction. Our study shows that functionalization at the 2‐position of azulene monomers influences polymer properties. For instance, different from electron‐withdrawing groups that discourage the protonation of azulene, electron‐donating aryl groups, however, enhances the sensitivity of response to acid. Protonation of the polymers leads to significant shifts in absorption spectra accompanying with obvious color changes from green to brown in majority cases because of the formation of poly(azulenium cation). The electrochromic properties of polymers are examined, exhibiting that nature of aryl group at the 2‐position of azulene influences the stability of their electrochromic devices.     

Study of the Air‐Tolerant 1,3‐Diphosphacyclobutane‐2,4‐diyl through the Direct Arylation

Installing π‐functional substituents on the skeletal phosphorus atoms of the air‐tolerant 1,3‐diphosphacyclobutane‐2,4‐diyl unit are promising for tuning the open‐shell singlet P‐heterocyclic chromophore. The sterically encumbered 1,3‐diphosphaCycloButen‐4‐yl Anion ( CBA ), generated from the phosphorus‐carbon triple bond, was available for the regioselective arylation via nucleophilic aromatic substitution (S_NAr) reaction, addition to arynes, and single‐electron transfer (SET) process affording the corresponding P‐arylated 1,3‐diphosphacyclobutane‐2,4‐diyls. The photo‐absorption and redox properties correlated with the effects of the aryl substituents on the 1,3‐diphosphacyclobutane‐2,4‐diyl unit. The X‐ray analyses enabled not only to discuss the metric parameters but also to visualize the radicalic electrons via the electron‐density distribution analysis. The electron‐donating character of the P‐heterocyclic chromophores induced the p‐type semiconductor behavior. Detection of hydrogen fluoride via formation of the 1λ⁵,3λ⁵‐diphosphete derivative was also developed.     

A Near‐Infrared Dye That Undergoes Multiple Interconversions through Acid–Base Equilibrium and Reversible Redox Processes

A near‐infrared (NIR) polymethine dye ( 1 ), consisting of a cyclohepta[1,2‐b ;4,3‐b′ ]dithiophene and two phenol moieties, was synthesized. This dye exhibited pH‐responsive changes in its photophysical properties due to a two‐step acid–base equilibrium that produced a protonated cation ( 1H⁺ ) and an anion ( 1⁻ ). While 1H⁺ showed an intense fluorescence in the red region of the visible spectrum, 1⁻ exhibited a strong absorption in the NIR region. The tropylium ion character in 1H⁺ induces high pK _a1 and pK _a2 values for 1 . Moreover, a stable radical ( 1^. ) was prepared, which showed a NIR absorption band with a maximum at circa 1600 nm. The cyclic voltammogram of 1^. revealed a two‐step reversible redox process that produced 1⁻ and the cation 1⁺ , which is different from 1H⁺ . These redox processes accompany drastic electrochromic changes in the vis–NIR region. Overall, 1 is susceptible to multiple interconversions between five forms, due to the multifaceted character of the cycloheptadithiophene skeleton.     

1,1,4,4-tetranitrobutane-2,3-diol and its derivatives. 2. Chlorination and bromination of 1,1,4,4-tetranitrobutane-2,3-diol. crystal structure of halogen derivatives of 1,1,4,4-tetranitrobutane-2,3-diol

The bromination of 1,1,4,4-tetranitrobutane-2,3-diol in 60% acetic acid gave 1,4-dibromo-1,1,4,4-tetranitrobutane-2,3-diol in satisfactory yield. The chlorination of 1,1,4,4-tetranitrobutane-2,3-diol under analogous conditions gave 1,4-dichloro-1,1,4,4-tetranitrobutane-2,3-diol as a crystal hydrate. Drying of this latter product in vacuum over phosphorus pentoxide gave 1,4-dichloro-1,1, 4,4-tetranitrobutane-2,3-diol in quantitative yield. The structures of these products were determined by x-ray diffraction structural analysis. The crystal chemical analysis and quantum chemical calculations established an increase in secondary oxygen-halogen interactions in the halodinitromethyl fragment with increasing atomic number of the halogen atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2372–2380, October, 1991.     

Effect of conjugated core building block dibenzo[a,c]phenazine unit on π‐conjugated electrochromic polymers: Red‐shifted absorption

A comparative investigation was undertaken for the electrosynthesis and electrochemical properties of three different electroactive polymers having a conjugated core building block, dibenzo[a,c]phenazine. A series of monomers has been synthesized as regards to thiophene based units; thiophene, 3‐hexyl thiophene, and 3,4‐ethylenedioxythiophene. The effects of different donor substituents on the polymers' electrochemical properties were examined by cyclic voltammetry. Introducing highly electron‐donating (ethylene dioxy) group to the monomer enables solubility while also lowering the oxidation potential. The planarity of the monomer unit enhances π‐stacking and consequently lowering the E_g from 2.4 eV (PHTP) to 1.7 (PTBP). Cyclic voltammetry and spectroelectrochemical measurements revealed that 2,7‐bis(4‐hexylthiophen‐2‐yl)dibenzo[a,c]phenazine (HTP) and 2,7‐bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)dibenzo[a,c]phenazine (TBP) possessed electrochromic behavior. The colorimetry analysis revealed that while PTBP have a color change from red to blue, PHTP has yellow color at neutral state and blue color at oxidized state. Hence the presence of the phenazine derivative as the acceptor unit causes a red shift in the polymers' absorption to have a blue color. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1714–1720, 2010     

Bright,Fluorescent Dyes Based on Imidazo[1,2‐a]pyridines that are Capable of Two‐Photon Absorption

A library of imidazo[1,2‐a]pyridines was synthesized by using the Gevorgyan method and their linear and non‐linear optical properties were studied. Derivatives that contained both electron‐donating and electron‐withdrawing groups at the 2 position were comprehensively investigated. Their emission quantum yield ranged between 0.2–0.7 and it was shown to depend on the substitution pattern, most notably that on the phenyl ring. Electron‐donating substituents improved the luminescence performance of these compounds, whereas electron‐withdrawing substituents led to a more erratic behavior. Substitution on the six‐membered ring had less effect on the fluorescence properties. Extension of the delocalization increased the luminescence quantum yield. A new quadrupolar system was designed that contained two imidazo[1,2‐a]pyridine units on its periphery and a 1,4‐dicyanobenzene unit at its center. This system exhibited a large Stokes‐shifted luminescence that was affected by the polarity and rigidity of the solvent, which was ascribed to emission from an excited state with strong charge‐transfer character. This quadrupolar feature also led to an acceptable two‐photon absorption response in the NIR region.     

Light‐Harvesting Organic Photoinitiators of Polymerization

Two new photoinitiators with unprecedented light absorption properties are proposed on the basis of a suitable truxene skeleton where several UV photoinitiators PI units such as benzophenone and thioxanthone are introduced at the periphery and whose molecular orbitals MO can be coupled with those of the PI units: a red‐shifted absorption and a strong increase of the molecular extinction coefficients (by a ≈ 20–1000 fold factor) are found. These compounds are highly efficient light‐harvesting photoinitiators. The scope and practicality of these photoinitiators of polymerization can be dramatically expanded, that is, both radical and cationic polymerization processes are accessible upon very soft irradiation conditions (halogen lamp, LED…︁) thanks to the unique light absorption properties of the new proposed structures.     

Wurster’s Blue‐type Cation Radicals Framed in a 5,10‐Dihydrobenzo[a]indolo[2,3‐c]carbazole (BIC) Skeleton: Dual Electrochromism with Drastic Changes in UV/Vis/NIR and Fluorescence

Electron‐donating dihydrobenzindolocarbazoles (BICs) 1 a – c , which adopt planar disk‐shaped geometries, were prepared by gold(I)‐catalyzed cyclization as a key step. Due to the presence of a 1,4‐phenylenediamine (PD) moiety in the framework, they undergo reversible one‐electron oxidation to the corresponding Wurster’s Blue (WB)‐type species that exhibits NIR absorptions up to λ=1200 nm. In the case of the N,N′‐dimethyl derivative, cation radical 1 c ^+. is stable enough to be isolated as a salt and X‐ray analysis indicated paraquinoid‐type bond alternation in the WB core unit, whereas the bond lengths in the peripheral benzene rings are identical to those in the neutral donor. Upon electrochemical interconversion, the redox pairs of 1 a – c and 1 a – c ^+. exhibited an electrochromic response in the UV/Vis/NIR region, which was accompanied by a drastic change in the fluorescence spectrum because only neutral donors 1 a – c are highly emissive (Φ_F: 0.7–0.8).     

New electrochromic polymeric pyridinium salts

A series of new anode-cathode conjugated electrochromic polymeric pyridinium salts containing mainchain triphenylamine units and demonstrating multicolor electrochromism has been synthesized. All of the polymers exhibit intense UV absorption with maxima of absorption and fluorescence at 340–343 and 336–338 nm in DMF solutions and 460–461 and 410–438 nm in films. The electrochromic properties of the films are investigated by electrochemical and spectroelectrochemical methods. Reversible redox signals with stable electrochromic characteristics are found in cyclic voltamperograms. The electrochromic properties of the polymers remain highly stable after 50 cycles in the range 0–1.2 V.     

Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)‐Substituted Bispyridinylidene

A new ground‐state organic electron donor has been prepared that features four strongly π‐donating iminophosphorano substituents on a bispyridinylidene skeleton. Cyclic voltammetry reveals a record redox potential of ?1.70 V vs. saturated calomel electrode (SCE) for the couple involving the neutral organic donor and its dication. This highly reducing organic compound can be isolated (44 %) or more conveniently generated in situ by a deprotonation reaction involving its readily prepared pyridinium ion precursor. This donor is able to reduce a variety of aryl halides, and, owing to its redox potential, was found to be the first organic donor to be effective in the thermally induced reductive S? N bond cleavage of N,N‐dialkylsulfonamides, and reductive hydrodecyanation of malonitriles.     

Dramatically Enhanced Solubility of Halide‐Containing Organometallic Species in Diiodomethane: The Role of Solvent⋅⋅⋅Complex Halogen Bonding

In the current study, we evaluated the solubility of a number of organometallic species and showed that it is noticeably improved in diiodomethane when compared to other haloalkane solvents. The better solvation properties of CH₂I₂ were associated with the substantially better σ‐hole‐donating ability of this solvent, which results in the formation of uniquely strong solvent–(metal complex) halogen bonding. The strength of the halogen bonding is attenuated by the introduction of additional halogen atoms in the organometallic species owing to the competitive formation of more favourable intermolecular complex–complex halogen bonding. The exceptional solvation properties of diiodomethane and its inertness towards organometallic species make this solvent a good candidate for NMR studies, in particular, for the acquisition of spectra of insensitive spins.     

基于吡咯并吡咯二酮和苯并噻二唑聚合物的合成及其近红外电致变色性能

给-受体型窄带隙聚合物是一类新型可见-近红外电致变色材料,虽然可调性强、颜色丰富,但是其电致变色性能如对比度、稳定性等需要进一步提高。 通过调节聚合物中构筑单元吡咯并吡咯二酮(DPP)、苯并噻二唑(BTZ)和噻吩(T)的比例(n(DPP):n(BTZ):n(T)分别为1:0:1、1.5:0.5:1、2:1:1和3:2:1),合成了4种新型窄带隙电致变色聚合物,研究聚合物结构和电致变色性能的关系。 研究发现,这类聚合物在近红外光谱区具有较高的对比度(ΔT:50%60%)和变色效率(CE:300600 cm²/C),尤其是在1550 nm处,聚合物P3的ΔT高达63%、P4的CE高达471 cm²/C。 相比之下,含有BTZ基团的聚合物的吸收更长、对比度更高且更稳定。 这为设计给-受体型高性能电致变色聚合物提供了新的思路。     

Dimeric Tetrathiafulvalene Linked to pseudo‐ortho‐[2.2]Paracyclophane: Chiral Electrochromic Properties and Use as a Chiral Dopant

A dimeric tetrathiafulvalene installed into a chiral pseudo‐ortho‐[2.2]paracyclophane framework was synthesized as a novel chiral electrochromic material. This compound exhibited pronounced chiroptical properties in the UV‐Vis‐NIR range depending on its redox states without racemization. Each enantiomer was examined as a chiral dopant for nematic liquid crystals (LCs), and the induced helicity of the LC solvent was in accord with that of the tetrathiafulvalene compound.     

Synthetic Control of Spectroscopic and Photophysical Properties of Triarylborane Derivatives Having Peripheral Electron‐Donating Groups

The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl‐ or trianthrylborane) and peripheral electron‐donating groups (N,N‐diphenylamino or 9H‐carbazolyl groups). The triarylborane derivatives with and without the electron‐donating groups showed intramolecular charge‐transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron‐donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron‐donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core.     

Experimental and theoretical investigation of a new rapid switching near‐infrared electrochromic conjugated polymer

A new rapid switching near‐IR electrochromic conjugated propeller‐shape polymer (PBTPAFL) with lower oxidation potential containing a di‐triarylamine group was synthesized via Suzuki coupling approach. The observed UV‐vis‐NIR absorption changes in the PBTPAFL film at various potentials are fully reversible and associated with strong color changes from the original light green to dark green and then to a Prussian blue. Excellent continuous cyclic stability of the electrochromic characteristics with a rapid color switching time 2.58 s and bleaching time 1.76 s was found as well. Compared with P1 and P2, the introduction of more electron‐donating propyl phenyl group in the para position of PBTPAFL lowered the oxidative potential and prevented coupling reaction during the electrochromic procedure. The high molecular weight conjugated polymer having high thermal stability with T_d10 more than 450 °C has excellent solubility in common organic solvents such as NMP, THF, chloroform, toluene, xylene, and benzene at room temperature (25 °C) due to the propeller‐shape structure and long alkyl chain on fluorene. Herein, from the combination of the experimental and computational study, we proposed a mechanism on the basis of the molecular orbital theory to explain the electrochromic oxidation behavior. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3913–3923, 2010.     

Functionalization of Quinoxalines by Using TMP Bases: Preparation of Tetracyclic Heterocycles with High Photoluminescene Quantum Yields

Tetracyclic heterocycles that exhibit high photoluminescence quantum yields were synthesized by anellation reactions of mono‐, di‐, and trifunctionalized 2,3‐dichloroquinoxalines. Thus, treatment of 2,3‐dichloroquinoxaline with TMPLi (TMP=2,2,6,6‐tetramethylpiperidyl) allows a regioselective lithiation in position 5. Quenching with various electrophiles (iodine, (BrCl₂C)₂, allylic bromide, acid chloride, aryl iodide) leads to 5‐functionalized 2,3‐dichloroquinoxalines. Further functionalization in positions 6 and 8 can be achieved by using TMPLi or TMPMgCl ? LiCl furnishing a range of new di‐ and tri‐functionalized 2,3‐dichloroquinoxalines. The chlorine atoms are readily substituted by anellation with 1,2‐diphenols or 1,2‐dithiophenols leading to a series of new tetracyclic compounds. These materials exhibit strong, tunable optical absorption and emission in the blue and green spectral region. The substituted O‐heterocyclic compounds exhibit particularly high photoluminescence quantum yields of up to 90 %, which renders them interesting candidates for fluorescence imaging applications.     

A Near-Infrared Dye That Undergoes Multiple Interconversions through Acid–Base Equilibrium and Reversible Redox Processes

A near-infrared (NIR) polymethine dye ( 1 ), consisting of a cyclohepta[1,2-b;4,3-b′]dithiophene and two phenol moieties, was synthesized. This dye exhibited pH-responsive changes in its photophysical properties due to a two-step acid–base equilibrium that produced a protonated cation ( 1H⁺ ) and an anion ( 1⁻ ). While 1H⁺ showed an intense fluorescence in the red region of the visible spectrum, 1⁻ exhibited a strong absorption in the NIR region. The tropylium ion character in 1H⁺ induces high pK_a1 and pK_a2 values for 1 . Moreover, a stable radical ( 1^. ) was prepared, which showed a NIR absorption band with a maximum at circa 1600 nm. The cyclic voltammogram of 1^. revealed a two-step reversible redox process that produced 1⁻ and the cation 1⁺ , which is different from 1H⁺ . These redox processes accompany drastic electrochromic changes in the vis–NIR region. Overall, 1 is susceptible to multiple interconversions between five forms, due to the multifaceted character of the cycloheptadithiophene skeleton.     

Comparative Analysis of Conjugated Alkynyl Chromophore–Triazacyclononane Ligands for Sensitized Emission of Europium and Terbium

A series of europium and terbium complexes based on a functionalized triazacyclononane carboxylate or phosphinate macrocyclic ligand is described. The influence of the anionic group, that is, carboxylate, methylphosphinate, or phenylphosphinate, on the photophysical properties was studied and rationalized on the basis of DFT calculated structures. The nature, number, and position of electron‐donating or electron‐withdrawing aryl substituents were varied systematically within the same phenylethynyl scaffold in order to optimize the brightness of the corresponding europium complexes and investigate their two‐photon absorption properties. Finally, the europium complexes were examined in cell‐imaging applications, and selected terbium complexes were studied as potential oxygen sensors.     

Electrochromic Poly(chalcogenoviologen)s as Anode Materials for High‐Performance Organic Radical Lithium‐Ion Batteries

A series of electrochromic electron‐accepting poly(chalcogenoviologen)s with multiple, stable, and reversible redox centers were used as anodic materials in organic radical lithium‐ion batteries (ORLIBs). The introduction of heavy atoms (S, Se, and Te) into the viologen scaffold significantly improved the capacity and cycling stability of the ORLIBs. Notably, the poly(Te‐BnV) anode was able to intercalate 20 Li ions and showed higher conductivity and insolubility in the electrolyte, thus contributing to a reversible capacity of 502 mAh g^?1 at 100 mA g^?1 when the Coulombic efficiency approached 100 %. The charged/discharged state of flexible electrochromic batteries fabricated from these anodic materials could be monitored visually owing to the unique electrochromic and redox properties of the materials. This study opens a promising avenue for the development of organic polymer‐based electrodes for flexible hybrid visual electronics.