π-Electron-system-layered polymer: through-space conjugation and properties as a single molecular wire

[2.2]Paracyclophane-based through-space conjugated oligomers and polymers were prepared, in which poly(p-arylene-ethynylene) (PAE) units were partially π-stacked and layered, and their properties in the ground state and excited state were investigated in detail. Electronic interactions among PAE units were effective through at least ten units in the ground state. Photoexcited energy transfer occurred from the stacked PAE units to the end-capping PAE moieties. The electrical conductivity of the polymers was estimated using the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and investigated together with time-dependent density functional theory (TD-DFT) calculations, showing that intramolecular charge carrier mobility through the stacked PAE units was a few tens of percentage larger than through the twisted PAE units.     

Preparation and chemical properties of soluble π‐conjugated poly(aryleneethynylene) consisting of azabenzothiadiazole as the electron‐accepting unit

A soluble charge‐transfer type poly(aryleneethynylene), PAE‐AzaBzTdz , consisting of a highly electron‐accepting azabenzothiadiazole unit was prepared in 99% yield by palladium‐catalyzed polycondensation between 4,7‐dibromo‐2,1,3‐azabenzothiadiazole ( Br₂‐AzaBzTdz ) and 1,4‐diethynyl‐2,5‐didodecyloxybenzene. PAE‐AzaBzTdz showed a number‐average molecular weight, M_n, of 6000 in gel‐permeation chromatography analysis and had good thermal stability as measured by TGA. UV–vis spectrum of PAE‐AzaBzTdz exhibited an absorption peak at 529 nm in chloroform, and the absorption peak shifted to a longer wavelength (601 nm) in film. Addition of MeOH to a CHCl₃ solution of PAE‐AzaBzTdz led to aggregation of the polymer to form stable colloidal particles. Results of filtration experiments using 0.2 and 0.02 μm membranes supported aggregation of the polymer. Addition of trifluoroacetic acid (TFA) to a chloroform solution of PAE‐AzaBzTdz led to a red‐shift of the UV–vis peak from 529 to 640 nm. An X‐ray diffraction pattern of powdery PAE‐AzaBzTdz indicated that the polymer assumed a layer‐to‐layer stacked structure with an interlayer distance of 3.4 Å in the solid state. An X‐ray diffraction pattern of cast film of PAE‐AzaBzTdz revealed that the polymer molecules in the cast film were ordered on the surface of Pt plate with the dodecyl side chain oriented toward the surface of the Pt plate. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2975–2982, 2008     

Construction of Helically Stacked π‐Electron Systems in Poly(quinolylene‐2,3‐methylene) Stabilized by Intramolecular Hydrogen Bonds

π‐Stacked polymers, which consist of layered π‐electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π‐stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π‐stacked architecture based on poly(quinolylene‐2,3‐methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo‐copolymerization of an o‐allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted‐tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic‐force microscopy.     

Lifetime Shortening and Fast Energy‐Tansfer Processes upon Dimerization of a A‐π‐D‐π‐A Molecule

Time‐resolved fluorescence and transient absorption experiments uncover a distinct change in the relaxation dynamics of the homo‐dimer formed by two 2,5‐bis[1‐(4‐N‐methylpyridinium)ethen‐2‐yl)]‐N‐methylpyrrole ditriflate ( M ) units linked by a short alkyl chain when compared to that of the monomer M . Fluorescence decay traces reveal characteristic decay times of 1.1 ns and 210 ps for M and the dimer, respectively. Transient absorption spectra in the spectral range of 425–1050 nm display similar spectral features for both systems, but strongly differ in the characteristic relaxation times gathered from a global fit of the experimental data. To rationalize the data we propose that after excitation of the dimer the energy localizes on one M branch and then decays to a dark state, peculiar only of the dimer. This dark state relaxes to the ground state within 210 ps through non‐radiative relaxation. The nature of the dark state is discussed in relation to different possible photophysical processes such as excimer formation and charge transfer between the two M units. Anisotropy decay traces of the probe‐beam differential transmittance of M and the dimer fall on complete different time scales as well. The anisotropy decay for M is satisfactorily ascribed to rotational diffusion in DMSO, whereas for the dimer it occurs on a faster time scale and is likely caused by energy‐transfer processes between the two monomer M units.     

Synthesis and properties of through‐space conjugated polymers based on π–π stacked 1,3‐biarylpropane tethering units

Novel skipped‐π polymers in which the π‐components are connected with 2‐substituted trimethylene tethering units exhibit bathochromically shifted, broadened ultraviolet absorption with a unique lower‐energy absorption band and a largely red‐shifted fluorescent emission. These results suggest that through‐space π–π interactions owing to a stair‐like stacking substructure in these polymers extend the π‐conjugation of the components in the ground and excited states. As the photophysical properties of the polymers observed both in a solution and in a dried film are similar to those of the J‐aggregates of π‐molecules, these polymers may be considered as pseudo J‐stacking (or J‐like‐stacking) polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3412–3419     

Anionic polymerization of 2,7‐di‐t‐butyldibenzofulvene: Synthesis,structure, and photophysical properties of the oligomers with a π‐stacked conformation

2,7‐Di‐t‐butyldibenzofulvene (tBu₂DBF), a bulky dibenzofulvene derivative, was polymerized using n‐butyllithium as initiator in tetrahydrofuran at ?78 °C and in toluene at 0 °C. tBu₂DBF afforded mainly oligomers up to trimer even at [monomer]₀/[initiator]₀ = 20 ([monomer]₀ = 0.2 M) at ?78 °C and 0 °C, indicating that this monomer is much less reactive than dibenzofulvene (DBF), its parent compound. The reaction at the same [monomer]₀/[initiator]₀ ratio at an elevated [monomer]₀ gave a small amount of insoluble polymer. The oligomers indicated a hypochromic effect in the absorption spectra and only monomer emission in the fluorescent spectra. The conformation of the trimer and the dimer was examined by means of NOESY NMR spectra and semiempirical calculations. In the trimer conformation, the fluorene moieties of the central and the initiation‐side monomeric units were found to be closely stacked on top of each other, while the termination‐side monomeric unit appeared to be in a faster conformational dynamics compared with the other monomeric units. Although the dimer seemed to have a relatively flexible conformation, a π‐stacked structure appeared to be involved in the conformational dynamics to show hypochromicity. The results of this study suggest that the reported intramolecular excited dimer (excimer) formation of the poly‐ and oligo(DBF)s [J Am Chem Soc 2003, 125, 15474] is based on a slight, local conformational change upon photo absorption, leading to a closer π‐stacked alignment of two neighboring fluorene units than that in the ground state. Such a local conformational transition may be difficult for the tBu₂DBF trimer because of steric repulsion of the t‐butyl groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 561–572, 2006     

Para‐linked and meta‐linked cationic water‐soluble fluorene‐containing poly(aryleneethynylene)s: Conformational changes and their effects on iron–sulfur protein detection

Four para‐linked or meta‐linked cationic water‐soluble fluorene‐containing poly(aryleneethynylene)s (PAEs) were synthesized to investigate the solvent‐induced π‐stacked self‐assembly. These PAE backbones are composed of fluorenylene and phenylene units, which are alternatively linked by ethynylene bonds. UV–vis absorption and photoluminescence spectra were used to study their conformational changes as solvent was gradually changed from MeOH to H₂O. In pure water, with gradually increased meta‐phenylene content (0, 50, and 100%), they underwent a gradual transition process of conformation from disordered aggregate structure to helix structure, which was not compactly folded. Moreover, the polymer with an ammonium‐functionalized side chain on the meta‐phenylene unit appeared to adopt a more incompact or extended helix conformation than the corresponding one without this side chain. Furthermore, the conformational changes of these cationic PAEs in H₂O were used to study their effects on biological detection. Rubredoxin (Rd), a type of anionic iron–sulfur‐based electron transfer protein, was chosen to act as biological analyte in the fluorescence quenching experiments of these polymers. Preliminary results suggest that they all exhibit amplified fluorescence quenching, and that the polymer with more features of helix conformation tends to be quenched by Rd more efficiently. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5424–5437, 2006     

[2.2]paracyclophane‐based through‐space conjugated polymers with fluorescence quenchers

New [2.2]paracyclophane‐based through‐space conjugated polymers containing fluorescence quenchers such as anthraquinone and ferrocene units at the polymer termini were designed and synthesized. Their optical properties were investigated in detail. Fluorescence emission from the stacked π‐electron systems was effectively quenched by the stacked π‐electron systems at the polymer termini due to the energy and electron transfer through a single polymer chain; thus, the polymers acted as the molecular wire. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Semiconducting polymers from triphenylamine derivatives‐benzaldehyde polymers by oxidization with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ)

4‐Tolyldiphenylamine (TDPA) and N,N′‐diphenyl‐N,N′‐bis(4‐methylphenyl)‐1,1′‐biphenyl‐4,4′‐diamine (TPD), were reacted with benzaldehyde (BA) using p‐toluenesulfonic acid as a catalyst to yield linear polymers. The polymers were reacted with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) in tetrahydrofuran (THF) at room temperature. ¹H‐NMR showed that all the methine protons in the residue of BA were completely removed at the mole ratio of repeating unit : DDQ, 2 : 1. The resulting polymers showed good solubility in chloroform or THF. The reacted TDPA‐BA and TPD‐BA polymers gave new UV absorption peaks at 697.0 and 722.5 nm and showed reversible redox potentials about 0.994 and 1.021 V, respectively. Direct current (d.c.) conductivity of the reacted polymers was in the range of 10^?11 S/cm, which is more than two orders higher than the unreacted polymers. The polymer showed pentad split electron spin resonance (ESR) signal, whose concentration was one in 670 or 230 repeating unit for TDPA‐BA and TPD‐BA polymers, respectively. Copyright © 2001 John Wiley & Sons, Ltd.     

Bulky side chain effect of poly(N‐vinylcarbazole)‐based stacked polymer electrets on device performance parameters of transistor memories

Three poly(N‐vinylcarbazole) (PVK)‐based polymer electrets were synthesized through Friedel‐Crafts postfunctionalization for the function of charge storage in nonvolatile organic field effect transistor (OFET) memory devices. The bulky side chain effect of these stacked polymer electrets on the morphology, water contact angles, and memory characteristics were examined with regard to those of precursor PVK. The introduction of steric hindrance groups could interrupt the large length of π‐stacked structures in PVK and block the form of region‐regular structures from region‐random on external electric field. As a result, the memories based on the three modified polymers exhibited approximate memory windows of 32 V increased by 13 V with respect to PVK. Besides, the write‐read‐erase‐read cycles stability of the modified polymers was superior to that of PVK. Furthermore, we found that the holes were mainly located in the region of local π‐stacked structures and bulky π‐conjugated groups also acted as additional electron trapping sites. Molecular engineering of charge trapping site with tunneling polymers will be a promise strategy for the advance of transistor memory. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3554–3564     

Soluble polymers with pendant 3‐en‐1‐yne groups (R) on a —[CH2—C(Me)R]n— skeleton by anionic polymerization of 2,5‐dimethylhexa‐1,5‐dien‐3‐yne

The anionic homopolymerization of 2,5‐dimethylhexa‐1.5‐dien‐3‐yne (DMDEY) was investigated by utilizing butyllithium, sec‐butyllithium, diphenylmethylsodium, and naphthalene/sodium as initiators. Soluble polymers with molecular weights up to 50 000 g/mol corresponding to M_w/M_n of 1.05 were obtained through homopolymerization with diphenylmethylsodium as initiator in THF at low temperatures. The homopolymers consist of 1,2‐linked monomer units with pendant 3‐methylbut‐3‐en‐1‐yne groups.     

Two‐sided comb poly(amic ester)–poly(propylene oxide) graft copolymers as porous polyimide precursors

New step‐growth graft block copolymers were synthesized. These two‐sided comb copolymers consisted of a poly(amic ester) (PAE) backbone and pendant poly(propylene oxide) (PPO) grafts. The copolymers were made via a macromonomer approach, in which the 4,6‐bischlorocarbonyl isophthalic acid bis[poly(propylene oxide)] ester macromonomer was synthesized through the reaction of hydroxyl‐terminated PPO oligomers with pyromellitic dianhydride and oxalyl chloride. This macromonomer was subsequently used in step‐growth polymerization with comonomers 4,6‐bischlorocarbonyl isophthalic acid diethyl ester, 2,5‐bischlorocarbonyl terephthalic acid diethyl ester, and 2,2‐bis[4‐ (4‐aminophenoxy)phenyl] hexafluoropropane, and this yielded PPO‐co‐PAE graft copolymers. Accordingly, we report the synthesis and characterization of the PPO oligomer, the PPO macromonomer, and their corresponding PPO‐co‐PAE graft copolymers. Graft copolymers with PPO concentrations of 3–26 wt % were synthesized. These polymers were thermally cured to produce polyimide/PPO composites. The thermolysis of these polyimide/PPO composites yielded porous polyimide films with porosities ranging of 4–22.5%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2266–2275, 2005     

Assembly of Multi‐Phthalocyanines on a Porphyrin Template by Fourfold Rotaxane Formation

A stacked assembly composed of a porphyrin and two phthalocyanines was prepared through fourfold rotaxane formation. Two phthalocyanine molecules, bearing four 24‐crown‐8 units, were assembled onto a porphyrin template incorporating four sidechains with two dialkylammonium ions each through pseudorotaxane formation between crown ether units and ammonium ions. The Staudinger phosphite reaction, as the stoppering reaction, resulted in the formation of the stacked heterotrimer composed of a porphyrin and two phthalocyanines connected through a fourfold rotaxane structure. UV/Vis spectroscopic and electrochemical studies of the heterotrimer indicated that there is a significant electronic interaction between the two phthalocyanine units due to the close stacking. The electrochemical oxidation process of the stacked heterotrimer was studied by cyclic voltammetry and spectroelectrochemistry. Electron paramagnetic resonance (EPR) spectroscopy of a dinuclear Cu^II complex, in which two Cu^II phthalocyanines were assembled on a metal‐free porphyrin template, revealed that two Cu^II phthalocyanines were located within the stacking distance, which resulted in an antiferromagnetic interaction between the two S= spins in the ground state of the Cu²⁺ ions in the heterotrimer.     

Synthesis and properties of conjugated polymers containing 3,9‐ and 2,9‐linked carbazole units in the main chain

Novel conjugated polymers containing 3,9‐ or 2,9‐linked carbazole units in the main chain were synthesized by the polycondensation of ethynyl‐ and iodo‐substituted 9‐arylenecarbazolylene monomers, and their optical and electrical properties were studied. Polymers with weight‐average molecular weights of 3400–12,000 were obtained in 76–99% yields by the Sonogashira coupling polycondensation in piperidine or tetrahydrofuran (THF)/piperidine at 30 °C for 48 h. All the 3,9‐linked polymers absorbed light around 300 nm. The para‐phenylene‐linked polymer also absorbed light around 350 nm, while meta‐phenylene‐linked one did not. The 3,9‐linked polymers absorbed light at a wavelength longer than the 2,9‐linked one. The polymers emitted blue fluorescence with high quantum yields (0.21–0.78) upon excitation at the absorption maxima. The polymers were oxidized around 0.6 V, and reduced around 0.5 V. Poly( 1 ) showed the dark conductivity of 3.7 × 10^?11 S/cm (10³ V/cm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3506–3517, 2009     

Metal Free Acid‐Mediated Solid‐State Polymerization and Processability of Polymers Based on 3,4‐Alkylenedioxythiophenes

The present article reports metal free acid‐mediated polymerization of 3,4‐alkylenedioxythiophenes in a solvent free medium and processability of insoluble polymers. It also describes structural variants and functional aqueous dispersions based on 3,4‐alkylenedioxythiophenes. Polymers were processed by dispersing the insoluble polymer powders in aqueous media using polymeric aromatic surfactant (polystyrenesulfonate, PSS) and aliphatic surfactant (sodiumdodecylsulfonate, SDS), respectively. The effect of surfactant on particle size, stability, and conductivity of the dispersions was investigated in detail. Polymer particles in SDS‐based dispersions tend to agglomerate which resulted enhanced conductivity of the thin films. Electrochemical studies revealed that the polymers are electroactive in nature and are transparent in oxidized state. The electrochromic contrast between the oxidized and reduced states of the polymers was in the range of 40–46%. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 783–791     

基于1,2-二氢-2-(4-羧基苯基-4-[4-(4-羧基苯氧基)-3-甲基苯基](2H)二氮杂萘-1-酮的新型芳香聚酰胺的简易合成

A new monomer diacid, 1,2-dihydro-2-(4-carboxylphenyl)-4-[4-(4-carboxylphenoxy)-3-methylphenyl]phtha-lazin-1-one (3), was synthesized through the aromatic nucleophilic substitution reaction of a readily available unsymmetrical phthalazinone 1 bisphenol-like with p-chlorobenzonitrile in the presence of potassium carbonate in N,N-dimethylacetamide and alkaline hydrolysis. The diacid could be directly polymerized with various aromatic diamines 4a-4e using triphenyl phosphite and pyridine as condensing agents to give five new aromatic poly(ether amide)s 5a-5e containing the kink non-coplanar heterocyclic units with inherent viscosities of 1.30-1.54 dL/g.The polymers were readily soluble in a variety of solvents such as N,N-dimethylformamide (DMF), N,N-dimethyl-acetamide (DMA), dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidinone (NMP), and even in m-cresol and pyridine (Py). The transparent, flexible and tough films could be formed by solution casting. The glass transition tem-peratures Tg were in the range of 286-317℃.     

Regio‐ and stereoselective cyclopolymerization of 1,2 : 4,5‐dianhydro‐3‐O‐methyl‐xylitol leading to a novel polycarbohydrate of (2→5)‐1,4‐anhydro‐3‐O‐methyl‐pentitol

(2→5)‐1,4‐Anhydro‐3‐O‐methyl‐pentitol, which is a novel carbohydrate polymer without an anomeric linkage, was synthesized by cationic cyclopolymerization of 1,2 : 4,5‐dianhydro‐3‐O‐methyl‐xylitol. When BF₃·OEt₂ was used as the initiator, soluble polymers were obtained in 28 to 50% yield. These polymers have number‐average molecular weights of 1 150 to 2 340 corresponding to an average degree of polymerization of 8.8 to 18.0. It was confirmed by ¹³C NMR that the resulting polymer mainly consists of 1,4‐anhydro‐3‐O‐methyl‐D L ‐arabinitol units.     

Investigation on thermoresponsive behavior of biodegradable poly(γ‐glutamic acid)‐graft‐L‐phenylalanine ethyl ester

The thermosensitivity of biodegradable and non‐toxic amphiphilic polymer derived from a naturally occurring polypeptide and a derivative of amino acid was first reported. The amphiphilic polymer consisted of poly(γ‐glutamic acid) (γ‐PGA) as a hydrophilic backbone, and L ‐phenylalanine ethyl ester (L ‐PAE) as a hydrophobic branch. Poly(γ‐glutamic acid)‐graft‐L ‐phenylalanine (γ‐PGA‐graft‐L ‐PAE) with grafting degrees of 7–49% were prepared by varying the content of a water‐soluble carbodiimide (WSC). γ‐PGA‐graft‐L ‐PAE with a grafting degree of 49% exhibited thermoresponsive phase transition behavior in an aqueous solution at around 80°C. The copolymers with grafting degrees in the range of 30–49% showed thermoresponsive properties in NaCl solution. A clouding temperature (T_cloud) could be adjusted by changing the polymer concentration and/or NaCl concentration. The thermoresponsive behavior was reversible. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and Self‐Assembly of Cyclic 2,7‐Anthrylene Ethynylene 1,3‐Phenylene Ethynylene Trimer with a Planar Conformation

Cyclic arylene ethynylene hexamer 1 , composed of alternating 2,7‐anthrylene ethynylene units and meta‐phenylene ethynylene units, was synthesized. It shows C₃ symmetry and possesses a flat and rigid conformation with a large equilateral triangle‐like cavity. Macrocycle 1 self‐associates through π–π stacking interactions between the anthracene‐containing macrocyclic aromatic cores with indefinite‐association constant K_E=6980 m ^?1 in CDCl₃ at 303 K. Macrocycle 1 also self‐assembles into π‐stacked nanofibers in the drop‐cast film.     

The preparation of 3,6‐bis(3‐hexylthien‐2‐yl)‐s‐tetrazine and its conjugated polymers

We demonstrated, for the first time, that 3,6‐bis(3‐hexylthien‐2‐yl)‐s‐tetrazine (TTz) with hexyl group at the 3‐position of thiophene rings can be prepared using a modified sulfur‐assisted Pinner synthesis. Although the hexyl group creates large steric hindrance to the tetrazine ring formation reaction, and the reaction under a traditional condition only produces trace amount of the target product, the yield of this reaction under a modified reaction condition using anhydrous hydrazine at 68 °C can reach 65%. Two new copolymers of the resulting TTz and hexyl‐ or 2‐ethylhexyl‐substituted cyclepentadithiophene have been prepared. The polymers show a broader light absorption in film than in solution attributing to the large distribution of effective conjugation length of polymer chain due to the existence of both cis‐ and trans‐orientations of the 3‐hexylthiophene units in the planar polymer chain in solid state. Although the polymers show a narrow band gap and a deep HOMO level, which are desirable for generating an efficient light absorption and a larger open circuit voltage (V_oc) of the resulting solar cell devices, the device performance is not as good as expected. It is attributed to the random distribution of the cis‐ and trans‐conformations along the polymer chain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.