Thiophene-based redox-active self-assembled monolayers (SAMs) were prepared on gold substrates. The alkanethiol derivatives of 1TPh-OC12SH and ETPh-OC12SH contain thiophene (1T) and 3,4-ethylenedioxythiophene (ET) units, respectively, with unprotected (nonsubstituted) thiophene α-carbons. PhETPh-OC12SH contains the ET unit, and all thiophene carbons are protected. Using these thiophene alkanethiol derivatives, we characterized the effect of thiophene carbon protection on the redox behavior of the thiophene SAMs by cyclic voltammetry. The formation of SAMs was confirmed by X-ray photoelectron spectroscopy and reflective IR. The IR peaks in the fingerprint region were assigned with the help of DFT calculations. Although 1TPh-OC12SH and ETPh-OC12SH SAMs lost their electrochemical activity during the first anodic scan, PhETPh-OC12SH SAMs are stable and maintain their electrochemical activity for at least 1200 redox cycles.

We report the synthesis of two novel poly(ionic liquid)s having poly(ethylene glycol) main chains and side chains having either one or two 1,2,3-triazolium cations with triethylene glycol spacers and bis(trifluoromethylsulfonyl)imide counter anion(s). Both ion conducting polymers are obtained by post-polymerization sequential modifications, i.e. copper-catalyzed azide–alkyne cycloaddition and N-alkylation of the 1,2,3-triazole group(s), starting from a common poly(ethylene glycol) (PEG) having azidomethyl side groups. The structures of the obtained polymers are supported by 1H NMR spectroscopy and size exclusion chromatography (SEC). The impact of the number of 1,2,3-triazolium groups and the structure of the spacer are discussed based on solubility, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and broadband dielectric spectroscopy (BDS) measurements. The dicationic derivative has a lower glass transition temperature (Tg = −27 °C) as well as higher thermal stability (Td10 = 369 °C) and ionic conductivity (σDC ∼ 10−5 S cm−1 at 30 °C under anhydrous conditions) than the monocationic analogue.

Oligomers of tetra(ethylene glycol)-disubstituted phenyl-capped bithiophene (Ph2TPh) linked by catechol and resorcinol were prepared. Catechol and resorcinol link the monomers via the ortho- and meta-positions of the benzene ring, respectively, and function as turning points in the folding process of the polymer. It was confirmed that the ortho-linked 8mer (o-8mer) and meta-linked 8mer (m-8mer) could form nanosheets through the self-assembly of folded polymers in o-dichlorobenzene. We confirmed that the arrangement of thiophene units inside the nanosheets was controllable by changing the chemical structure of the turning point. The different arrangements of the Ph2TPh units led to changes in other physical properties such as UV-Vis absorption, nanosheet thickness and charge carrier transport. The absorption spectrum of the o-8mer nanosheets suggested that the Ph2TPh units are arranged vertical to the lateral direction of the nanosheets. On the other hand, the Ph2TPh units in the m-8mer nanosheets were considered to have a tilted orientation. The change in the Ph2TPh tilt angle inside the nanosheets was supported by the different thicknesses of the o-8mer and m-8mer nanosheets. The relationship between the absorption spectrum and Ph2TPh unit arrangement was discussed based on the DFT calculation. Intrinsic charge carrier transport properties were evaluated by a noncontact microwave-based method. The o-8mer nanosheets showed higher conductivity than the m-8mer and triazole-linked-8mer nanosheets. The lifetime of charge carriers in the nanosheet was longer than that in the lamellar structure of the drop-cast film.

A series of glycidyl-polymer-based poly(ionic liquid)s (cationic GTPs) was synthesized via the click functionalization of a glycidyl azide polymer with alkyne derivatives of ionic liquids. Three types of cationic moieties (imidazolium, pyridinium and pyrrolidinium) and two types of spacers between the 1,2,3-triazole and cationic moiety (C4H8 alkyl chain (C4) and tetra(ethylene glycol) (EG4)) were examined. The cationic GTPs were characterized by NMR, IR, differential scanning calorimetry, thermogravimetric analysis and impedance spectroscopy. From the gel permeation chromatography analysis of the model polymer, the weight-average molecular weights of cationic GTPs were estimated to be 0.8–1.0 million Da. 1H NMR analysis of the partially decomposed polymer confirmed that the thermal decomposition of the cationic GTPs with the C4 spacer begins with the detachment of the cationic moiety. Compared with the C4 spacer, the EG4 spacer decreases the glass transition temperature and increases the ionic conductivity. The cationic GTP with the EG4 spacer, pyrrolidinium cationic moiety and bis(trifluoromethanesulfonyl)imide (Tf2N) counter anion exhibited the highest anhydrous ionic conductivity (1.1 × 10−5 S cm−1 at 30 °C and 1.1 × 10−3 S cm−1 at 120 °C). The conducting ion concentration and mobility were estimated by electrode polarization analysis. The imidazolium moiety gives a relatively higher conducting ion concentration because of the lower binding energy with the Tf2N counter anion. Compared with other GTPs, the pyridinium GTPs showed greater temperature dependences of their conducting ion mobilities.

The oligomers consisting of phenyl-capped bithiophene and tetra(ethylene glycol)s linked by azide–alkyne Huisgen cycloaddition were synthesized. The relationship between the degree of polymerization and self-assembling ability was investigated in o-dichlorobenzene and dimethyl sulfoxide. From the absorption spectrum, it was confirmed that the critical degree of polymerization (CDP) for thiophene unit aggregation was 4. The morphology of the aggregated product was observed by atomic force microscopy. The oligomers 4mer and 5mer could not self-assemble into well-defined structures due to the weak driving force for the self-assembly. In the cases of 6mer and 7mer, aggregates with nonwell-defined and nanosheet structures coexisted. In the cases of 8mer and 9mer, the nanosheet was the main product. The critical point between 7mer and 8mer could be confirmed by different aggregation behaviors in the cooling process of the solution (nonsigmoidal and sigmoidal). In the cases of 8mer and 9mer, polymer folding prior to intermolecular self-assembly, which was supported by sigmoidal aggregation behavior, leads to the nanosheet formation. On the contrary, shorter oligomers than 8mer experience intermolecular aggregation prior to intramolecular polymer folding, which was supported by the nonsigmoidal aggregation behavior. This is the first report to prove the existence of CDP for folded polymer nanosheet formation which requires hierarchical self-assembly, i.e., polymer folding followed by intermolecular self-assembly.

Thiophene-based redox-active self-assembled monolayers (SAMs) were prepared on gold substrates. The alkanethiol derivatives of 1TPh-OC12SH and ETPh-OC12SH contain thiophene (1T) and 3,4-ethylenedioxythiophene (ET) units, respectively, with unprotected (nonsubstituted) thiophene α-carbons. PhETPh-OC12SH contains the ET unit, and all thiophene carbons are protected. Using these thiophene alkanethiol derivatives, we characterized the effect of thiophene carbon protection on the redox behavior of the thiophene SAMs by cyclic voltammetry. The formation of SAMs was confirmed by X-ray photoelectron spectroscopy and reflective IR. The IR peaks in the fingerprint region were assigned with the help of DFT calculations. Although 1TPh-OC12SH and ETPh-OC12SH SAMs lost their electrochemical activity during the first anodic scan, PhETPh-OC12SH SAMs are stable and maintain their electrochemical activity for at least 1200 redox cycles.

•Phenyl-capped cyclohexa[c]thiophenes (nCHT) have been synthesized and characterized.•nCHT is the first model compound to poly(nCHT).•nCHT has nice redox activity.•nCHT has twisted conformation at the neutral state.•DFT calculation supports the improved conjugation length at oxidized state.A series of phenyl-capped cyclohexa[c]thiophene derivatives (nCHT-TEG, n = 2, 4, or 6) have been synthesized. nCHT-TEG are well-soluble in common organic solvents. The absorption spectra of neutral nCHT-TEG oligomers indicated a shorter effective conjugation length than conventional oligothiophenes based on the non-coplanarity of the thiophene rings. nCHT-TEG can be oxidized/reduced reversibly. The results of cyclic voltammetry and UV–Vis–NIR spectroscopy of the oxidized nCHT-TEG revealed that the effective conjugation length increases at the higher oxidation state. Density functional theory (DFT) calculations indicate that the quinoidal structure of the oxidized nCHT contributes to the improved effective conjugation length. nCHT-TEG radical cations and dications were characterized by electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopies, respectively. NMR results of nCHT-TEG dication revealed that 2CHT-TEG2+ have closed-shell bipolaron structure, while 4CHT-TEG2+ and 6CHT-TEG2+ are the mixture of closed-shell bipolaron and open-shell two-polaron structures.

A supramolecular organogel was prepared by mixing the glycidyl triazole polymers (GTP) functionalized with crown ether and secondary ammoniumion at the side groups. The polymers form an organogel above a concentration of 3 wt % via physical cross-links of the inclusion complex. The organogel responds to multiple stimuli, e.g., temperature, acid/base, and chemical species. The number of the effective cross-links estimated from the storage modulus and the affine network model suggests that some part of the binding sites could not work as the physical cross-links. Rheological measurement under large deformation showed that the storage modulus was constant up to 250% strain and larger than the loss modulus up to 600% strain. The high elasticity of the gel is attributable to the material design based on the high-molecular-weight flexible glycidyl polymers with many binding sites in the single polymer chain. The organogel also showed nice self-healing behavior. The molecular diffusion in the gel network was characterized by fluorescence correlation spectroscopy. Although the cross-link of the organogel has dynamic nature due to inclusion complexation, the diffusion behavior of the low-molecular-weight fluorescence tracer was similar to that observed in chemically cross-linked gels.

The electrochromic properties of a polythiophene polyrotaxane film consisting of a polythiophene backbone wrapped by the tetra-cationic cyclophane, cyclobis(paraquat-p-phenylene), were characterized. A naked reference polythiophene film, i.e., polythiophene without tetra-cationic cyclophane, was also characterized. The surface morphology and thickness of the film (L) were observed by atomic force microscopy. The surface of the naked reference polythiophene film has micrometer-scale polythiophene aggregates, which causes the darker color of the film and smaller color contrast in the electrochromic process. The polythiophene polyrotaxane gives a more homogeneous and brighter colored film owing to the suppression of molecular interactions between the polythiophene chains by the tetra-cationic cyclophanes. Potential-step chronoamperometric measurement provided the area density of the oxidizable sites (Γ) and the apparent diffusion coefficient of the charge transport in the film. From linear relationship between L and Γ, the concentrations of the oxidizable sites in the polythiophene polyrotaxane and naked reference polythiophene films were calculated to be 1.3 and 2.4 mmol cm−3, respectively. Interestingly, the polythiophene polyrotaxane film afforded a significantly larger apparent diffusion coefficient than the naked reference polythiophene film. This result suggests that the rate-determining step of the charge transport is not the electron hopping between the polythiophene chains but the transport of charge-compensating counterions from the solvent into the polythiophene. We believe that the counteranions of the tetra-cationic cyclophane provide a pathway allowing the charge-compensating counteranions to migrate from the solvent to polythiophene. The polythiophene polyrotaxane film showed faster color change than the naked reference polythiophene film in the electrochromic reaction. These results indicate that our polythiophene polyrotaxane is a better electrochromic material than the naked reference polythiophene.

The polythiophene polyrotaxane was synthesized through electrochemical polymerization of the [2]rotaxane consisting of the electron-rich dumbbell-shaped sexithiophene and the electron-deficient cyclophane of cyclobis(paraquat-p-phenylene). The optical and electrochemical property of the polythiophene polyrotaxane film was characterized. The material reported herein is attractive not only as a component for constructing the macromolecular machine but also as a new type of insulated molecular wire having donor−acceptor interaction between the macrocycle and the conductive polymer.

The inclusion complexation between the electron-poor cyclophane, i.e. cyclobis(paraquat-p-phenylene), and the electron-rich thiophene oligomers, i.e. thiophene, bithiophene and terthiophene, were characterized in solution and solid state. In solution, we confirmed a 1:1 complexation and that the binding strength depends on the number of the thiophene units. From the X-ray crystallographic analysis we confirmed the solid-state structure of the inclusion complex. These results indicate that charge-transfer, π–π and van der Waals interactions may contribute to the driving force of inclusion complexation.

In this paper, we reveal that the free-base and zinc strapped porphyrins possessing long alkyl chains, C24OPP-HQ and Zn(C24OPP-HQ), respectively, can be arranged on surfaces. We used scanning tunneling microscopy (STM) to observe alkyl-chain-assisted self-assembled monolayers (SAMs) of these strapped porphyrins at the solid−liquid interface. STM images revealed that the strapped benzene moiety was detectable on the porphyrin core: that is, the strapped porphyrins could be differentiated from nonstrapped analogues. We compared the population of the nonstrapped porphyrin (C24OPP) and either of the strapped porphyrins C24OPP-HQ or Zn(C24OPP-HQ) in the mixed SAMs. We then confirmed that Zn(C24OPP-HQ) is more favorably incorporated in the mixed SAMs than C24OPP-HQ. From 1H NMR spectroscopic and X-ray crystallographic analyses, we concluded that the factors increasing the population of Zn(C24OPP-HQ) in the mixed SAMs are the enhanced rigidity of the porphyrin core by the zinc coordination and the flat structure of the porphyrin moiety in the saddle conformation. This study demonstrates that strapped porphyrins possessing long alkyl chains are available to arrange the functional modules on the surface via chemical modification on the strapped moiety.