Structure−Property Relations of Regiosymmetrical 3,4-Dioxy-Functionalized Polythiophenes

We present the synthesis and characterization of novel homo- and copolymers containing mono- and dialkylated 3,4-propylenedioxythiophenes with the purpose of creating new π-conjugated polymers to be exploited in the field of polymer electronics and photonics. We show that the large seven-membered dioxepine ring attached to the thiophene moiety causes unfavorable steric interactions, especially in the homopolymers; it thus prevents the polymers from adapting a coplanar structure with a short π-stacking distance in the solid state. We furthermore show that incorporation of less space filling units in the form of unsubstituted thiophene units into the polymer chain reduces these unfavorable interactions and therefore allows for a more coplanar polymer backbone orientation and a shorter π-stacking distance in the solid state. These findings are based on absorption spectroscopy, electrochemical measurements, X-ray powder diffraction, and conductivity measurements

New Regiosymmetrical Dioxopyrrolo- and Dihydropyrrolo-Functionalized Polythiophenes

We present the synthesis of two N-alkylated poly(dioxopyrrolothiophene)s and two N-alkylated poly(dihydropyrrolothiophene)s with potential application in the field of conducting polymers. The polymers are synthesized from the corresponding 2,5-dibromothiophenes by an Ullmann-type polymerization and a Stille-type polymerization, respectively. The two N-alkylated poly(dihydropyrrolothiophene)s are the first examples of amino-functionalized polythiophenes built from regiosymmetrical thiophene monomers

Effect of Fluorination of 2,1,3-Benzothiadiazole

The 4,7-dithieno-2,1,3-benzothiadiazole (DTBT) moiety and its fluorinated counterpart are important π-conjugated building blocks in the field of organic electronics. Here we present a combined experimental and theoretical investigation into fundamental properties relating to these two molecular entities and discuss the potential impact on extended π-conjugated materials and their electronic properties. While the fluorinated derivative, in the solid state, packs with a cofacial overlap smaller than that of DTBT, we report experimental evidence of stronger optical absorption as well as stronger intra- and intermolecular contacts upon fluorination

Post-Polymerization Ketalization for Improved Organic Photovoltaic Materials

Poor organic photovoltaic device performance of a ketone-functionalized benzotrithiophene polymer with desirable frontier energy levels and a broad absorption in the visible region is successfully addressed through a new postpolymerization ketalization approach. Hereby, the initial ketone-functionalized polymer is converted to two different ketal derivatives, which show superior processability leading to significantly enhanced photovoltaic device performance

Discrete Photopatternable π-Conjugated Oligomers for Electrochromic Devices

Three discrete oligomeric systems including an all-thiophene (T6) system, a thiophene/phenylene (TPTTPT) system, and a thiophene/EDOT/phenylene (TPEEPT) system have been constructed and characterized with emphasis on structural, optical, electrochemical, and spectroelectrochemical properties. For all three chromophores, the radical cation, the dication, and the π-dimer have been identified and characterized. EPR spectroscopy reveals that the radical cations of TPTTPT and TPEEPT have g values of 2.008−2.012 and peak-to-peak widths in the range 4.2−5.3 G. Formation of the radical cation takes place at a lower potential for TPEEPT than for TPTTPT and T6, whereas subsequent oxidation to the dication occurs more easily for TPTTPT than for TPEEPT and T6. We ascribe this observation to more localized charges in the oxidized species of TPEEPT, which is supported by our finding that the radical cation of TPEEPT is less prone to undergo π-dimerization than the radical cations of TPTTPT and T6. All the oxidized species are sufficiently stable to allow for optical characterization, and the relative positions of all absorption bands are found to be in agreement with the electrochemical data. For further solid-state modifications of these materials, we have effectively modified the synthetic design and grafted terminal functionalities (e.s. acrylates) onto the discrete oligomers. Of these novel materials, TPEEPT proves to be the most promising anodically coloring material for electrochromics, and it undergoes reversible switching between two different colored states (bright yellow and clear blue) and one almost transparent and color neutral state. Contrast ratios, measured as Δ%T at λmax, are as high as 62.5%, and switching times are in the range 2−5 s for the coloration process, though significantly longer for the bleaching process. As a proof of concept, we have successfully constructed a simple photopatterned electrochromic device by exploiting the terminal acrylate functionalities of the oligomers in a UV-initiated cross-linking process. To the best of our knowledge, this is the first oligomer-based photopatterned electrochromic device reported in the literature

Discrete Photopatternable π-Conjugated Oligomers for Electrochromic Devices

Three discrete oligomeric systems including an all-thiophene (T6) system, a thiophene/phenylene (TPTTPT) system, and a thiophene/EDOT/phenylene (TPEEPT) system have been constructed and characterized with emphasis on structural, optical, electrochemical, and spectroelectrochemical properties. For all three chromophores, the radical cation, the dication, and the π-dimer have been identified and characterized. EPR spectroscopy reveals that the radical cations of TPTTPT and TPEEPT have g values of 2.008−2.012 and peak-to-peak widths in the range 4.2−5.3 G. Formation of the radical cation takes place at a lower potential for TPEEPT than for TPTTPT and T6, whereas subsequent oxidation to the dication occurs more easily for TPTTPT than for TPEEPT and T6. We ascribe this observation to more localized charges in the oxidized species of TPEEPT, which is supported by our finding that the radical cation of TPEEPT is less prone to undergo π-dimerization than the radical cations of TPTTPT and T6. All the oxidized species are sufficiently stable to allow for optical characterization, and the relative positions of all absorption bands are found to be in agreement with the electrochemical data. For further solid-state modifications of these materials, we have effectively modified the synthetic design and grafted terminal functionalities (e.s. acrylates) onto the discrete oligomers. Of these novel materials, TPEEPT proves to be the most promising anodically coloring material for electrochromics, and it undergoes reversible switching between two different colored states (bright yellow and clear blue) and one almost transparent and color neutral state. Contrast ratios, measured as Δ%T at λmax, are as high as 62.5%, and switching times are in the range 2−5 s for the coloration process, though significantly longer for the bleaching process. As a proof of concept, we have successfully constructed a simple photopatterned electrochromic device by exploiting the terminal acrylate functionalities of the oligomers in a UV-initiated cross-linking process. To the best of our knowledge, this is the first oligomer-based photopatterned electrochromic device reported in the literature

Discrete Photopatternable π-Conjugated Oligomers for Electrochromic Devices

Three discrete oligomeric systems including an all-thiophene (T6) system, a thiophene/phenylene (TPTTPT) system, and a thiophene/EDOT/phenylene (TPEEPT) system have been constructed and characterized with emphasis on structural, optical, electrochemical, and spectroelectrochemical properties. For all three chromophores, the radical cation, the dication, and the π-dimer have been identified and characterized. EPR spectroscopy reveals that the radical cations of TPTTPT and TPEEPT have g values of 2.008−2.012 and peak-to-peak widths in the range 4.2−5.3 G. Formation of the radical cation takes place at a lower potential for TPEEPT than for TPTTPT and T6, whereas subsequent oxidation to the dication occurs more easily for TPTTPT than for TPEEPT and T6. We ascribe this observation to more localized charges in the oxidized species of TPEEPT, which is supported by our finding that the radical cation of TPEEPT is less prone to undergo π-dimerization than the radical cations of TPTTPT and T6. All the oxidized species are sufficiently stable to allow for optical characterization, and the relative positions of all absorption bands are found to be in agreement with the electrochemical data. For further solid-state modifications of these materials, we have effectively modified the synthetic design and grafted terminal functionalities (e.s. acrylates) onto the discrete oligomers. Of these novel materials, TPEEPT proves to be the most promising anodically coloring material for electrochromics, and it undergoes reversible switching between two different colored states (bright yellow and clear blue) and one almost transparent and color neutral state. Contrast ratios, measured as Δ%T at λmax, are as high as 62.5%, and switching times are in the range 2−5 s for the coloration process, though significantly longer for the bleaching process. As a proof of concept, we have successfully constructed a simple photopatterned electrochromic device by exploiting the terminal acrylate functionalities of the oligomers in a UV-initiated cross-linking process. To the best of our knowledge, this is the first oligomer-based photopatterned electrochromic device reported in the literature

Influence of the Alkyl Mantle on the Self-Assembly of Phenylene−Thienylene-Based Oligomers

The organization of a series of phenylene−thienylene-based oligomers solubilized with terminal (ω-hydroxyalkyl) and lateral (alkoxy) side chains was studied. The thermal behavior and self-assembly on the surface during solution and thermal processing are mainly affected by the position and length of the side chains. The molecules organize in different fashions, depending on the substitution pattern, as indicated by fiber X-ray scattering results. The oligomer with only lateral side chains behaves as a typical rigid rod arranged in lamella structures, while those with a homogeneous alkyl mantle around the aromatic system adapt a disklike character and form one-dimensional stacks. Because of the large aromatic rod, the role of the terminal hydroxy groups on the self-assembly can be neglected. The choice of the alkyl density around the aromatic core allows a control over the molecular organization, which is essential for the development of high-performance solution-processable organic semiconductors

Molecular Tuning of Phenylene-Vinylene Derivatives for Two-Photon Photosensitized Singlet Oxygen Production

Substituent-dependent features and properties of the sensitizer play an important role in the photosensitized production of singlet oxygen, O2(a1Δg). In this work, we systematically examine the effect of molecular changes in the sensitizer on the efficiency of singlet oxygen production using, as the sensitizer, oligophenylene-vinylene derivatives designed to optimally absorb light in a nonlinear two-photon process. We demonstrate that one cannot always rely on rule-of-thumb guidelines when attempting to construct efficient two-photon singlet oxygen sensitizers. Rather, as a consequence of behavior that can deviate from the norm, a full investigation of the photophysical properties of the system is generally required. For example, it is acknowledged that the introduction of a ketone moiety to the sensitizer chromophore often results in more efficient production of singlet oxygen. However, we show here that the introduction of a carbonyl into a given phenylene-vinylene can, rather, have adverse effects on the yield of singlet oxygen produced. Using these molecules, we show that care must also be exercised when using qualitative symmetry-derived arguments to predict the relationship between one-and two-photon absorption spectra

One- and Two-Photon Photosensitized Singlet Oxygen Production: Characterization of Aromatic Ketones as Sensitizer Standards

Singlet molecular oxygen, O2(aΔg), can be efficiently produced in a photosensitized process using either one- or two-photon irradiation. The aromatic ketone 1-phenalenone (PN) is an established one-photon singlet oxygen sensitizer with many desirable attributes for use as a standard. In the present work, photophysical properties of two other aromatic ketones, pyrene-1,6-dione (PD) and benzo[cd]pyren-5-one (BP), are reported and compared to those of PN. Both PD and BP sensitize the production of singlet oxygen with near unit quantum efficiency in a nonpolar (toluene) and a polar (acetonitrile) solvent. With their more extensive π networks, the one-photon absorption spectra for PD and BP extend out to longer wavelengths than that for PN, thus providing increased flexibility for sensitizer excitation over the range ∼300−520 nm. Moreover, PD and BP have much larger two-photon absorption cross sections than PN over the range 655−840 nm which, in turn, results in amounts of singlet oxygen that are readily detected in optical experiments. One- and two-photon absorption spectra of PD and BP obtained using high-level calculations model the salient features of the experimental data well. In particular, the ramifications of molecular symmetry are clearly reflected in both the experimental and calculated spectra. The use of PD and BP as standards for both the one- and two-photon photosensitized production of singlet oxygen is expected to facilitate the development of new sensitizers for application in singlet-oxygen-based imaging experiments