Supramolecular PEDOT∙CB7-PS polypseudorotaxane and PEDOT∙CB7-PR polyrotaxane were prepared by threading the cucurbit[7]uril (CB7) molecules over the 3,4-ethylenedioxythiophene (EDOT) monomer, followed by oxidative polymerization . The dielectric parameters of these encapsulated compounds were investigated by means of broadband dielectric spectroscopy. The evolution of dielectric constant with frequency clearly emphasizes two distinct regimes, assigned with the space charge polarization (at low frequencies) and the ‘intrinsic’ dipolar activity (at high frequencies). The spectra of dielectric loss vs. frequency reveal a dominant signal for conductivity of free charge carriers. Furthermore, frequency dependences of conductivity profiles are strongly correlated with the dielectric constant and dielectric loss components and disclose the clear signal of electrical conductivity. The conductivity of PEDOT∙CB7-PR was found to be with one order of magnitude higher than that of the pristine PEDOT.
Poly(3,4-ethylenedioxythiophene/permethylated γ-cyclodextrin) polyrotaxane (PEDOT∙TMγCD) having bulky triphenylmethyl as stoppers was synthesized by the chemical oxidation of 3,4-ethylenedioxythiophene (EDOT) as an inclusion complex with 2,3,6-tri-O-methyl γ-cyclodextrin (TMγCD) (EDOT∙TMγCD) with a five-fold excess of iron (III) chloride oxidant over the stoichiometric amount in water. For a comparison, the reference PEDOT was synthesized under the same experimental conditions. The chemical structures of the synthesized compounds were proved by FT-IR and NMR spectroscopies. The coverage ratio of the EDOT and PEDOT backbones was found to be of 80.0 % and 43.7 %, respectively. Differential scanning calorimetry (DSC) studies of both PEDOT and PEDOT∙TMγCD samples showed no crystallization or melting peaks in the range 20-200 °C. The PEDOT∙TMγCD as dark-green powders was enough soluble in acetone, dichloromethane, CHCl3 and THF compared with those of the reference PEDOT. The optical properties of the PEDOT and PEDOT∙TMγCD compounds were investigated by UV-Vis. The UV-Vis absorption spectrum of PEDOT∙TMγCD in THF is consistent with the spectrum of the PEDOT in DMSO. Atomic force microscopy, AFM, indicated that the PEDOT∙TMγCD film is more uniformly distributed over the substrate area compared with those of the reference PEDOT. The electrochemical data provided that the investigated PEDOT∙TMγCD exhibited n- and p-doping processes. The HOMO/LUMO energy level indicates that the investigated PEDOT∙TMγCD polyrotaxane is electrochemically accessible as electron-transporting material in electronic devices.
We report the effect of the macrocyclic encapsulation on the photophysical properties of poly(9,9-dioctylfluorene-alt-bithiophene) polyrotaxanes copolymers. The encapsulated compounds were synthesized by Suzuki cross-coupling reaction between 5,5'-dibromo-2,2'-bithiophene (DBT) inclusion complexes in randomly methylated β-cyclodextrin (RM-βCD), 2,3,6-tri-O-methyl β-cyclodextrin (TM-βCD), 2,3,6-tri-O-trimethylsilyl β-cyclodextrin (TMS-βCD) or cucurbit[7]uril (CB7) with a bulky 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester (DF) as stoppers. These supramolecular compounds exhibited distinct improvement in the solubility, molecular weight, film forming ability, surface-morphological characteristics and reduced aggregation tendency compared to those of the neat compound. Also, the threading of conjugated backbones into macrocycles leads to an increasing environmental stability and resistance to quenching from impurities. Fluorescence emission (PL) shows vibronic transitions and a mono-exponential kinetics. The electrochemical data provided that the investigated compounds exhibited n- and p-doping processes. The encapsulation of DBT into TM-βCD or TMS-βCD cavities exhibits a greater effect on the LUMO, while the encapsulation into CB7 affects the HOMO energy levels. The HOMO/LUMO energy levels indicate that the investigated polyrotaxanes are electrochemically accessible as electron-transporting materials in electronic devices. Based on AFM analysis, polyrotaxane compounds exhibits a higher tendency to organize into fibers or linear ribbons.
Optical, electrochemical and surface-morphological properties of three terpolymer polyrotaxanes (1a, 1b and 1c) composed of 2,7-dibromo-9,9-dicyanomethylenefluorene encapsulated into γ-cyclodextrin (γCD), β- or γ-persilylated cyclodextrin (PS-γCD, PS-γCD) cavities (acceptor) and 4,4′-dibromo-4′′-methyltriphenylamine (donor) randomly distributed into 9,9-dioctylfluorene conjugated chains have been evaluated and compared to those of the reference 1. The role of the encapsulation on the thermal stability, solubility, film forming ability and transparency was also investigated. High fluorescence efficiency, almost identical normalized absorbance maximum in solution and solid-states of 1a, 1b and 1c provides the lower aggregation tendency. The fluorescence lifetimes (τ) of 1a, 1b and 1c follow a mono-exponential decay with a value τ = 1.11, 1.03 and 1.14 ns, compared with the neat 1, where a bi-exponential decay was identified. AFM studies reveal a smooth and homogenous surface morphology for polyrotaxanes than that of the reference. The electrochemical data provided that the investigated compounds exhibited n- and p-doping processes. The HOMO/LUMO energy levels 1a, 1b, 1c and 1 and in combination with the work function of anodic ITO glass substrates coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (-5.2 eV) and cathodic Ca (-2.8 eV) or Al (-2.2 eV) indicate that the compounds are electrochemically accessible as electron-transporting materials.
The photophysical properties of two polyazomethine polyrotaxanes (4•αCD and 4•TMS-αCD) composed of pyrene and triazole encapsulated into native and permodified α-cyclodextrin (αCD and TMS-αCD) cavities have been investigated and compared with those of the non-rotaxane 4 counterparts. Rotaxane formation results in improvements of the solubility in organic solvents, as well as better film forming ability combined with a high transparency. The polyrotaxane 4•TMS-αCD was soluble in toluene/DMF1/1 v/v mixture and displayed useful levels of thermal stability. The fluorescence spectroscopy of 4•αCD and 4•TMS-αCD shows an obvious blue shift both in excitation and emission spectra with respect to those of non-rotaxane counterparts. 4•TMS-αCD displays a continuous absorption spectrum, whereas the reference 4 does not show any absorption maximum, neither for its emission maximum, presumably because of its very low solubility in DMF. The improved fluorescence efficiency (ΦPL) of both polyrotaxanes is attributed to the hydrophobic micro-environment within αCD and TMS-αCD cavities. The surfaces of non-rotaxane 4 counterparts showed globular formations with an agglomeration tendency, while the encapsulated 4•αCD and 4•TMS-αCD rotaxane compounds exhibited smoother surfaces, comprised by smaller grains uniformly distributed on the surface of the solid films. The presence of the αCD and TMS-αCD in 4·αCD and 4•TMS-αCD polyrotaxanes affects the LUMO energy levels to a greater extent than its HOMO energy with respect to reference 4. The wetting properties of spin-coated film of 4•TMS-αCD in water (polar) and diiodomethane (apolar), indicates that TMS-αCD makes its surface more hydrophobic. The dispersive and polar components are lower than that of the reference compounds. The doping of the rotaxane structures with iodine (I2) indicated smaller improvements of electrical conductivity (σ) values, which presents a tradeoff with their better solubility, process ability, surface characteristics and ΦPL.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.