Janusz Kowalik

A technique to compare polythiophene solid-state dye sensitized TiO2 solar cells to liquid junction devices

In this communication, we report on a technique to fabricate solid-state polythiophenebased dye sensitized solar cells (DSSCs) that can be directly compared to analogous liquid junction devices. The device configuration is based on non-porous TiO2 thin films and one of the three undoped polythiophene hole conductors: poly[3-(11 diethylphosphorylundecyl) thiophene], P3PUT, poly(4-undecyl-2,2 0 -bithiophene), P4UBT, or poly(3-undecyl-2,2 0 -bithiophene), P3UBT. These polymers were spin coated and cast from organic solutions onto the TiO2 films. The dense TiO2 thin films (ca. 30 nm) were deposited on conductive glass via facile spray pyrolysis and sol–gel techniques. After that, cis-(SCN)2 Bis(2,2 0 bipyridyl-4,4 0 dicarboxylate) ruthenium(II) (a.k.a. Ru N3 dye) was adsorbed on the TiO2 surface, and the polythiophenes were utilized as hole conductors in a simplified solar cell geometry. The results were compared to the control DSSC device made with dense TiO2 and a liquid electrolyte, or

Topochemistry and photomechanical effects in crystals of green fluorescent protein-like chromophores: effects of hydrogen bonding and crystal packing.

To obtain insight into the effects of the environment on the photophysics and photochemistry of the green fluorescence protein (GFP), eight crystal structures of six synthetic aryl-substituted analogues (2-fluoro, 2-methyl, 3-hydroxy, 3-methoxy, 2,4-dimethyl and 2,5-dimethyl) of the GFP chromophore (4-hydroxy-benzylidenedimethylimidazolinone) were determined and correlated with their two-dimensional steady-state and time-resolved solid-state excitation-emission spectra. The stacking between the molecules greatly affected the emission energy and the lifetime of the emission of the chromophore, implying that pi-pi interactions could be critical for the photophysics of GFP. The reaction pathways were dependent on the excitation energy, resulting either in [2 + 2] photodimerization at the bridging double bond (UV excitation) or flipping of the imidazolone ring (visible excitation). The meta-hydroxy chromophore (3-HOBDI) was the only GFP-chromophore analogue that was obtained as more than one stable polymorph in the pure state thus far. Due to the asymmetric substitution with hydrogen bond donors and acceptors, 3-HOBDI is tetramorphic, the forms showing distinctly different structure and behavior: (1) while one of the polymorphs (3-HOBDI-A), having multilayer structure with alternating stereochemistry of linear hydrogen-bonded motifs, undergoes photodimerization under UV light, (2) another (3-HOBDI-C), which has dimeric head-to-tail structure, shows Z-to-E isomerization via tau-one-bond flip of the imidazolone ring by excitation in the visible region. X-ray diffraction analysis of a partially reacted single crystal of 3-HOBDI-C provided the first direct evidence of tau-one-bond flip occurring in a GFP-like compound. Moreover, the cooperative action of the photodimerization of 3-HOBDI-A appears as a photomechanical effect of unprecedented magnitude for a single crystalline specimen, where photoexcited single crystals bend to more than 90 degrees without breaking.

Characterization of nanocrystalline and thin film TiO2 solar cells with poly(3-undecyl-2,2′-bithiophene) as a sensitizer and hole conductor

We report on the use of poly(3-undecyl-2,2′-bithiophene) and three different types of TiO2 film layers to determine the dependence of photovoltaic performance on the morphology of the TiO2 films. It was observed that the TiO2 film morphology plays an important role in the performance of photovoltaic solar cells with polythiophene used as both sensitizer and hole conductor. The polymer was tested on a flat TiO2 layer made from a sol–gel process, a larger surface area TiO2 layer derived from an aqueous TiF4 solution, and a nanocrystalline thin TiO2 film. We observe over twice the improvement in short circuit current density in the nanocrystalline cells (jsc=233.6 μA cm−2) over that of the flat titania cells (89.8 μA cm−2). The best photocurrent density (448 μA cm−2) performance was from the TiF4 derived titania based cells when using the polymer. It was noted that soaking the nanocrystalline and TiF4 cells in the polymer for at least 24 h improves their overall performance, while no noticeable improvement is evident for the flat sol–gel derived cells. We explain our results by proposing that pore filling is likely to be easier in the TiF4 derived TiO2 due to larger pore sizes. Multiple reflections of light may also play an important role in the TiF4 titania films by enhancing the amount of light absorbed by the polymer. These observations suggest that the relative size of the sensitizer molecule and the pores of nanocrystalline films may be a critical factor to consider in designing photovoltaic devices such as solar cells based on nanoporous materials.

Poly(4-undecyl-2,2'-bithiophene) as a hole conductor in solid state dye sensitized titanium dioxide solar cells

Reference LPI-ARTICLE-2001-007doi:10.1016/S0379-6779(00)00650-0View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Isomerization in Fluorescent Protein Chromophores Involves Addition/Elimination

The green fluorescent protein (GFP) chromophore undergoes both photochemical and thermal isomerizations. Typically, the Z form is more stable and undergoes photochemical conversion to the E form followed by thermal reversion over a period of seconds or minutes. Although the mechanism of the thermal reversion has been the subject of some investigations, the surprisingly low activation energy for this process has not sparked any controversy. We now show that the chromophore is surprisingly stable in both E and Z forms and that the facile thermal reversion is the result of a novel nucleophilic addition/elimination mechanism. This observation may have implications for the intervention of such processes, as well as blinking and kindling, in fluorescent proteins.

Combining Scanning Electrochemical Microscopy with Infrared Attenuated Total Reflection Spectroscopy for In-situ Studies of Electrochemically Induced Processes

The combination of scanning electrochemical microscopy (SECM) with single-bounce attenuated total reflection Fourier-transformed infrared spectroscopy (FT-IR-ATR) has been developed for in situ studies on electrochemically induced processes at IR waveguide surfaces via evanescent field absorption spectroscopy. The feasibility of the combined microelectrochemical FT-IR setup was demonstrated by spectroscopically monitoring microstructured polymer depositions induced via feedback mode SECM using a 25 mum Pt disk ultramicroelectrode (UME). The surface of a ZnSe ATR crystal was initially coated with 2,5-di-(2-thienyl)-pyrrole (SNS) layer, which was then locally polymerized during Ru(bpy)(3)(2+) mediated feedback mode SECM experiments. The polymerization reaction was simultaneously monitored by recording absorption intensity changes of SNS specific IR bands, thereby providing information on the polymerization mechanism and on the percentage of surface modification.

Strongly adherent conductive heteropolymers

Abstract A number of “trimer” thiophenepyrrolethiophene monomers have been synthesized which allow incorporation of functionality at an N-alkyl group and which form semiconducting films upon electropolymerization. When the N-alkyl group is an alkanethiol, the resulting monomers attach strongly to gold or platinum surfaces and allow electropolymerization on the surface rather than precipitation after polymerization. Such polymerized films exhibit remarkable adherence to the metal surface, in contrast to unsubstituted monomers.

Electropolymerization of Bilayer with Phosphonic Acid Tethers for Immobilization of Biomolecules

Bilayer consisting of polypyrrole, PPy, as the inner and poly(2,5-dithienyl-(N-3-phosphorylpropyl)pyrrole, p(TPTC3-PO 3 H 2 ) as the outer layers was electropolymerized in layer-by-layer steps. Due to the presence of phosphonic acid functionality tethered to the backbone of outer polymer, the system is capable of binding organic and inorganic bases and offers an easy and convenient access to sensor devices. The ion transport through the polypyrrole film depends on its thickness. The thin layer of pTPTC3-PO 3 H 2 does not hinder the redox and ion-transport characteristics of the PPy layer.

Control of Chloride Ion Exchange by DNA Hybridization at Polypyrrole Electrode

Publisher Summary This chapter presents an approach based on the reversible transport of counter ions into or out of the polypyrrole (PPy) layer when it is electrochemically oxidized or reduced. The movement of ions is governed by doping and undoping of the polymer, satisfying the rule of charge neutrality at all redox states of the polymer. The PPy layer with the grafted pTPTC3PO 3 H 2 allows the Mg 2+ cation to form a bidentate complex between the phosponate group of TPTC3PO 3 H 2 and the phosphate group of the probe DNA. The chapter describes preparation, characterization, and testing of the probe. Most of the proof-of-principle, development and optimization work is done with a 27-mer oligonucleotide called “probe DNA”. The grafting of thin pTPTC3PO 3 H 2 layer on the PPy has been confirmed by FTIR and by X-ray photoelectron spectroscopy (XPS). Probing of the hybridization event is a two-step process. First, the probe DNA molecule is attached to the Mg 2+- modified bilayer. In the second step, dipping the electrode with the already attached probe DNA to the complementary target DNA solution achieves the hybridization. The selectivity of the response of the probe DNA modified electrode was tested against non-complementary DNA target.

Hydrogen bonding and cooperativity effects on the assembly of alkyl- and perfluoroalkyl-sulfonyl naphthols: F···F non-bonded interactions†

Important differences in the crystal packing of 6-perfluorohexylsulfonyl-2-naphthol (1F) including π–π stacking aromatic interactions and F···F non-bonded contacts, in contrast to its nonfluorinated analog (1), appear to translate into differences between their photophysical properties both in the solid state and in solution.