Jacek Gasiorowski

Electrocatalytic Reduction of Carbon Dioxide to Carbon Monoxide by a Polymerized Film of an Alkynyl‐Substituted Rhenium(I) Complex

The alkynyl‐substituted ReI complex [Re(5,5′‐bisphenylethynyl‐2,2′‐bipyridyl)(CO)3Cl] was immobilized by electropolymerization onto a Pt‐plate electrode. The polymerized film exhibited electrocatalytic activity for the reduction of CO2 to CO. Cyclic voltammetry studies and bulk controlled‐potential electrolysis experiments were performed by using a CO2‐saturated acetonitrile solution. The CO2 reduction, determined by cyclic voltammetry, occurs at approximately −1150 mV versus the normal hydrogen electrode (NHE). Quantitative analysis by GC and IR spectroscopy was used to determine a Faradaic efficiency of approximately 33 % for the formation of CO. Both values of the modified electrode were compared to the performance of the homogenous monomer [Re(5,5′‐bisphenylethynyl‐2,2′‐bipyridyl)(CO)3Cl] in acetonitrile. The polymer formation and its properties were studied by using SEM, AFM, and attenuated total reflectance (ATR) FTIR and UV/Vis spectroscopy.

(Photo)physical Properties of New Molecular Glasses End-Capped with Thiophene Rings Composed of Diimide and Imine Units

New symmetrical arylene bisimide derivatives formed by using electron-donating–electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N′-bis(5-aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5-thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69–0.90%.

Photosensitizing porphyrin–triazine compound for bulk heterojunction solar cells

This report describes the synthesis of a novel porphyrin–triazine compound bearing three porphyrin macrocycles connected to each other via a triazine central unit, and investigation of its properties for possible use in bulk heterojunction solar cells (BHJ-SCs). The porphyrin macrocycles serve as light harvesting antennae, while the triazines have been widely known to be charge extracting promoters. According to cyclic voltammetric studies, the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels of the target compound were estimated to be at −5.4 and −3.5 eV versus vacuum, respectively. Photoluminescence measurements of the blended films of the porphyrin–triazine compound and phenyl-C61-butyric acid methyl ester (PCBM) or poly(3-hexylthiophene) (P3HT) indicated that the charge transfer was possible when the target porphyrin was used as an electron donor together with PCBM as an acceptor. Additionally, the surface morphology of the films with different donor:acceptor ratios was investigated by atomic force microscopy (AFM). Upon variation of the donor:acceptor weight ratio and thickness of the organic layer, the short circuit current density (JSC) of the BHJ-SCs fabricated herein improved up to approximately 2.25 mA cm−2.

Rhodium-Coordinated Poly(arylene-ethynylene)-alt-Poly(arylene- vinylene) Copolymer Acting as Photocatalyst for Visible-Light- Powered NAD + /NADH Reduction

A 2,2′-bipyridyl-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene) polymer, acting as a light-harvesting ligand system, was synthesized and coupled to an organometallic rhodium complex designed for photocatalytic NAD+/NADH reduction. The material, which absorbs over a wide spectral range, was characterized by using various analytical techniques, confirming its chemical structure and properties. The dielectric function of the material was determined from spectroscopic ellipsometry measurements. Photocatalytic reduction of nucleotide redox cofactors under visible light irradiation (390–650 nm) was performed and is discussed in detail. The new metal-containing polymer can be used to cover large surface areas (e.g. glass beads) and, due to this immobilization step, can be easily separated from the reaction solution after photolysis. Because of its high stability, the polymer-based catalyst system can be repeatedly used under different reaction conditions for (photo)chemical reduction of NAD+. With this concept, enzymatic, photo-biocatalytic systems for solar energy conversion can be facilitated, and the precious metal catalyst can be recycled.

On the potential of porphyrin-spiked triarylamine stars for bulk heterojunction solar cells

A novel porphyrin–triarylamine compound was synthesized to serve as a photosensitizer in bulk heterojunction solar cells (BHJ-OSCs). Based on cyclic voltammetric analysis, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the target porphyrin trimer were determined to be at −5.4 and −3.5 eV versus vacuum, respectively, and compared with those of other materials used for the construction of the BHJ-OSCs. Absorption and emission spectra of the film of the target porphyrin trimer were in good agreement with those of its solution. The charge transfer in a blended film of the porphyrin–triarylamine compound with phenyl-C61-butyric acid methyl ester (PCBM) was proven possible by photoluminescence measurements. The energy conversion efficiency of the BHJ-OSCs based on the target compound depended strongly on the donor : acceptor weight ratio and the thickness of the organic layer. Surface nanomorphologies of the films with different donor : acceptor ratios and thickness were investigated by atomic force microscopy (AFM). The short circuit current density (JSC) up to 2.06 mA cm−2 was obtained from the BHJ-OSC fabricated herein.

Polydiacetylene-nested porphyrin as a potential light harvesting component in bulk heterojunction solar cells

A meso-substituted zinc-porphyrin embedded in a polydiacetylene web was prepared and tested for its potential in bulk heterojunction solar cells (BHJ-SCs). Light assisted formation of the polyenynes from diacetylenes coupled to the meso-position of the porphyrin were observed after UV-radiation, as evidenced by double and triple bond Raman-bands at 1446 and 2080 cm−1, respectively, and via UV absorption enhancement at 530–600 nm. Using cyclic voltammetry, Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels were determined to be in an appropriate range for the photoactive materials in BHJ-SCs. Indeed, photoluminescence quenching indicated energy and/or charge transfer when the target material was used as a donor in combination with phenyl-C61-butyric acid methyl ester as acceptor in a blend. A photovoltaic effect of the BHJ-SCs was observed.

Photoelectrochemical scanning droplet cell microscopy for localized photovoltaic investigations on organic semiconductors

Photoelectrochemical characterization of the regioregular poly(3-hexylthiophene) (P3HT) was performed using an adapted version of a photoelectrochemical scanning droplet cell microscope (PE-SDCM). The real and imaginary parts of the dielectric function were determined using spectroscopic ellipsometry in order to identify the absorption region of the polymer. Detailed photoelectrochemical experiments were performed for the thin polymer layer contacted with 0.1 M tetrabutylammonium hexafluorophosphate dissolved in propylene carbonate as well as with an electrolyte containing a 5.4 mM ferrocene/ferrocenium redox couple. The effect of the illumination on the P3HT covered WE in contact with both the pure electrolyte and an electrolyte containing a ferrocene/ferrocenium redox couple was studied using dark/illumination sequences. The stability of the photovoltaic effect was characterized using long term current transients. Finally, the photoelectrochemical impedance spectroscopy was applied to determine the electrical properties of the P3HT in the dark and under illumination.

Iodide‐Capped PbS Quantum Dots: Full Optical Characterization of a Versatile Absorber

Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their associated optical qualities are true for the colloidal solution phase, they change upon processing into thin-films. A detailed view to the optical key-parameters during solid-film development is presented and the limits and outlooks for this versatile and promising absorber are discussed.

Photoelectrochemical and Electrochemical Characterization of Sub- Micro-Gram Amounts of Organic Semiconductors Using Scanning Droplet Cell Microscopy

A model organic semiconductor (MDMO-PPV) was used for testing a modified version of a photoelectrochemical scanning droplet cell microscope (PE-SDCM) adapted for use with nonaqueous electrolytes and containing an optical fiber for localized illumination. The most attractive features of the PE-SDCM are represented by the possibility of addressing small areas on the investigated substrate and the need of small amounts of electrolyte. A very small amount (ng) of the material under study is sufficient for a complete electrochemical and photoelectrochemical characterization due to the scanning capability of the cell. The electrochemical behavior of the polymer was studied in detail using potentiostatic and potentiodynamic investigations as well as electrochemical impedance spectroscopy. Additionally, the photoelectrochemical properties were investigated under illumination conditions, and the photocurrents found were at least 3 orders of magnitude higher than the dark (background) current, revealing the usefulness of this compact microcell for photovoltaic characterizations.

Influence of molecular designs on polaronic and vibrational transitions in a conjugated push-pull copolymer

Electron-phonon interactions of free charge-carriers in doped pi-conjugated polymers are conceptually described by 1-dimensional (1D) delocalization. Thereby, polaronic transitions fit the 1D-Froehlich model in quasi-confined chains. However, recent developments in conjugated polymers have diversified the backbones to become elaborate heterocylcic macromolecules. Their complexity makes it difficult to investigate the electron-phonon coupling. In this work we resolve the electron-phonon interactions in the ground and doped state in a complex push-pull polymer. We focus on the polaronic transitions using in-situ spectroscopy to work out the differences between single-unit and push-pull systems to obtain the desired structural- electronic correlations in the doped state. We apply the classic 1D-Froehlich model to generate optical model fits. Interestingly, we find the 1D-approach in push-pull polarons in agreement to the model, pointing at the strong 1D-character and plain electronic structure of the push-pull structure. In contrast, polarons in the single-unit polymer emerge to a multi- dimensional problem difficult to resolve due to their anisotropy. Thus, we report an enhancement of the 1D-character by the push-pull concept in the doped state - an important view in light of the main purpose of push-pull polymers for photovoltaic devices.