Regiosymmetric poly(dialkylphenylenedioxythiophene)s: electron-rich, stackable pi-conjugated nanoribbons.
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Biomedical subjects
Wojciech Pisula
Publications and source records attributed to Wojciech Pisula.
From macro- to nanoscopic templating with nanographenes.
A hexa-peri-hexabenzocoronene carrying six long, branched alkyl chains has been processed in nano- and macroscopic pore templates. An extraordinary self-organization of this material was observed within macroscopically large glass capillaries after cooling from the isotropic phase. Thereby, the columnar structures were long-range aligned along the capillary axis over several centimeters. This behavior was explained by the pronounced directional self-assembly of the molecules, whereby the curvature effect of the capillary was negligible. The processing in nanoscopic pores of an inorganic membrane yielded an improved supramolecular organization. It was possible to remove the inorganic template and to obtain bundles and single nanorods. The templating over different dimensions opens a variety of potential applications.
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From armchair to zigzag peripheries in nanographenes.
Synthetic concepts toward the synthesis of large, not-fully benzenoid polycyclic aromatic hydrocarbons (PAHs), decorated with phase-forming and solubilizing n-dodecyl chains, are presented based on the intramolecular cyclodehydrogenation reaction of suitable oligophenylene precursors. The formal addition of successive C2 units into the armchair bays of the parent hexa-peri-hexabenzocoronene extends the aromatic system and leads to PAHs with a partial zigzag periphery. This variation of the nature of the periphery, symmetry, size, and shape has a distinct impact upon the electronic properties and the organization into columnar superstructures. Both computational and experimental UV/vis spectra, which are in good agreement, emphasize the dependence of the characteristic bands alpha, p, and beta upon the overall size and symmetry of the PAHs. While the number and the substitution patterns of attached n-dodecyl chains do not influence the electronic properties, the thermal behavior and supramolecular organization are strongly influenced, which has been elucidated with differential scanning calorimetry (DSC) and 2D wide-angle X-ray diffractometry (2D-WAXS) on mechanically aligned samples. This study provides valuable insight into the future design of semiconducting materials based on extended PAHs.
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A conjugated polycarbazole ring around a porphyrin.
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Suppressing aggregation in a large polycyclic aromatic hydrocarbon.
With the approach presented herein, a large aromatic pi-system is synthesized, which shows extraordinarily high solubility and an effective suppression of aggregation. This was due to a distortion of the aromatic core by bulky tert-butyl groups and the solubilizing effects of alkyl chains in the corona of the aromatic core. Therefore not only the processing and cleaning of the materials with standard laboratory techniques became possible, but moreover the first structure-rich UV/vis and a resolved (1)H NMR spectra for an aromatic system two times larger than hexa-peri-hexabenzocoronene were recorded. The bulk properties in an extruded fiber as well as on the surface showed a columnar self-assembly including a phase in which a homeotropic alignment on a substrate was observed, which turns the material into an interesting candidate for future applications in electronic devices.
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Pronounced supramolecular order in discotic donor-acceptor mixtures.
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Response to novelty of various types in laboratory rats.
One purpose of the two studies reported here was to examine the reactions of rats to changes in the spatial arrangement of a familiarized environment under low stress conditions. The second purpose was to test the role of rats' experience with novelty. In Experiment I the novelty was manipulated by introducing new tunnels into one zone of the experimental chamber. The introduction of novelty took place after 11 habituation sessions. In Experiment II in the course of habituation sessions the experimental group of rats was subjected to a persistent change of tunnel arrangement in the experimental zone, whereas for the control group nothing changed. All animals reacted to the novelty with increased time spent in the experimental zone and decreased time spent in other zones. Both experiments show that under low stress conditions rats demonstrate a positive response toward novelty and that their previous experience with novelty does not affect that reaction.
Animals↗
In situ studies of phase transitions in thin discotic films.
The crystalline to liquid crystalline (Cr-LC) phase transition in thin films of zone-cast hexa-peri-hexabenzocoronene sixfold substituted with dodecyl side chains (HBC-C12H25) has been studied in detail using grazing incidence X-ray diffraction (GID), electron diffraction (ED), and variable angle spectroscopic ellipsometry (VASE), When heating the material, a first minor transition is observed around 42 degrees C. This change is attributed to alterations of the crystalline alkyl chain packing, which only slightly changes the electronic properties of the material. At higher temperatures of about 90 degrees C, but still significantly below the previously reported transition temperature in bulk, the Cr-LC transition is observed. An accompanying large increase in optical anisotropy is compatible with the X-ray data, showing a transition from the as-cast herringbone-like crystalline state to a highly ordered discotic hexagonal columnar LC phase. The structural transition has the macroscopic effect of increasing the film thickness. The high structural order of the as-cast low-temperature phase is only partly recovered after cooling, and the phase transition exhibits a large hysteresis. From the ellipsometry data, the dielectric tensor of HBC-C12H25 was refined to unprecedented detail.
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Charge recombination via intercolumnar electron tunneling through the lipid-like mantle of discotic hexa-alkyl-hexa-peri-hexabenzocoronenes.
The recombination of the mobile charge carriers formed in pulse-ionized hexa-alkyl-substituted hexa-peri-hexabenzocoronenes occurs mainly via intercolumnar electron tunneling through the intervening hydrocarbon mantle. This is evidenced as a dramatic increase in the time scale of the decay of the radiation-induced conductivity from a few hundred nanoseconds to close to a millisecond as the peripheral alkyl substituents increase in size from 8 to 24 carbon atoms with corresponding disk diameters, D, from 23.4 to 36.6 A. The decay kinetics are a function only of the total number of peripheral carbon atoms with no evidence for specific effects of chain branching. The 1/e decay time, tau(e), increases exponentially with D according to tau(e) = tau(e)(0) exp(betaD) with tau(e)(0) = 48 fs and beta = 0.63 A(-1). Taking into account the tilted columnar configuration of the molecules in the solid phase leads to a beta value of ca. 0.8 A(-1) for the distance dependence of intercolumnar electron tunneling. In contrast to the orders of magnitude changes in the time scale for intercolumnar charge recombination, the intracolumnar charge hopping times vary by only a factor of 4, between 40 and 160 fs, with no systematic dependence on the nature of the alkyl substituents. On the basis of the results, the time scale estimated for electron tunneling across a 40 A thick lipid membrane is estimated to be close to 1 ms.
Electric Conductivity↗
Structure of zone-cast HBC-C12H25 films.
The structure of a thin zone-cast film of the hexa-n-dodecyl-substituted hexa-peri-benzocoronene (HBC) has been investigated using grazing incidence X-ray diffraction. A model with an orthorhombic unit cell containing two molecules accounts well for the observations. The molecules are arranged in a "herringbone" structure resembling the packing observed for unsubstituted HBC. The molecular disk planes are oriented perpendicularly to the substrate, rotated by approximately 39 degrees about the film normal. The relatively long side chains of dodecyl were found to be in an ordered interdigitated state. The aliphatic side chains and the aromatic HBC-cores segregate to form regular vertical domains spanning the film thickness. For in-plane rocking scans a discrete orientation distribution is observed with peaks at regular angle intervals. We interpret this as a grain boundary effect induced by alkyl chain stacking faults.
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Influence of alkyl substituents on the solution- and surface-organization of hexa-peri-hexabenzocoronenes.
Three hexa-peri-hexabenzocoronenes (HBCs) with branched, bulky alkyl substituents of different lengths in the periphery of the aromatic core have been synthesized to tune the self-association properties in solution. 1H NMR and photophysical measurements were used to probe the solution organization in comparison to the known hexa-dodecyl-substituted HBC in different solvent systems. Thermodynamic parameters for the self-association in solution, obtained by curve fitting of the concentration- and temperature-dependent NMR data using van't Hoff analysis, indicated that the self-association is an enthalpically driven process that is entropically disfavored. Photoluminescence and NMR results were both employed to determine the critical concentration where no self-association for different compounds occurred. The interactions between the molecules could be controlled by varying the nonsolvent content in the solvent mixtures, supporting the model of solvophobic effects. The spatial demand of the solubilizing side chains modulated the self-association in solution. This behavior was translated into the solution casting process, where the kinetic in addition to the thermodynamic parameters played an essential role for structure formation. The study illuminates the relationship between the solution association of HBCs and the morphology, when processed on a surface. These results are essential for the application of these materials in devices.
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Exploratory behavior as a function of environmental novelty and complexity in male and female rats.
Laboratory rats show a positive response to low- and nonstressful novel events. The novel event may involve a number of aspects of the stimulus field. It is usually associated with a change in amount of environmental complexity. Most studies concerning novelty-related behavior involve the introduction of novel objects or the rearrangement of familiar objects. The present purpose was to measure exploratory behavior in response to environments of increased and decreased complexity. Both directions of environmental change are conditions of novelty. A two-way manipulation of increasing and decreasing the complexity of the environment was used. Rats of both sexes showed increased exploration to exposure to novelty, no matter which manipulation was applied; however, female and male rats behaved differently to the two types of novelty. Males responded more to novelty from the introduction of an unfamiliar object. The results indicate novel stimulation, whether of increasing or decreasing complexity, has reward properties. Perhaps the male-specific behavior directed toward unfamiliar objects may serve an adaptive function.
Animals↗
Exceptionally long-range self-assembly of hexa-peri-hexabenzocoronene with dove-tailed alkyl substituents.
The substitution of a hexa-peri-hexabenzocoronene by bulky, space-demanding, 2-decyltetradecyl side chains proved to be an effective procedure to influence the thermal and self-aggregation behavior. The extremely large steric requirement of the introduced side chains modulated the aggregation and resulted in a dramatic lowering of the isotropization temperature and a higher solubility. As an additional consequence of the exceptional, long-range self-aggregation of the discotic molecule, spherulite formation was observed during crystallization by polarized light microscopy. Macroscopic self-assembly was induced by zone crystallization of the material, leading to aligned columnar superstructures as revealed by 2D-WAXS experiments. These extraordinary properties have not yet been reported for a discotic columnar material, making this compound very promising for application in electronic devices.
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Comparative psychology, a new perspective for the 21st century: up the spiral staircase.
This article responds to the continuing obituaries for Comparative Psychology. We understand the field to be a general psychology, a way of understanding the origins of all behavior of all species. We outline a methodological and conceptual foundation for comparative psychology to enter the new millennium-with an anagenetic and dynamic systems perspective. We see an important role to be played by comparative psychologists in managing resources, increasing our activity in social and political issues, and transcending our traditional role as the study of animal behavior to one that makes significant contributions to psychology and humanity by studying relationships between animals and changing environments, and by providing a historical perspective on human evolution.
Animals↗
The Roman high- and low-avoidance rats respond differently to novelty in a familiarized environment.
The purpose of the present study was to investigate the response to novelty in Roman high- and low-avoidance rats under non-stressful conditions. To reduce fear, a procedure of repetitive placing in the experimental chamber consisting of start, screen, and tunnel zones was applied. Each animal was placed in the experimental chamber daily for a 6min period. The first 11 sessions were the habituation sessions. In the 12th session, the novelty was introduced into the screen and tunnel zones. The subsequent two sessions were conducted under novelty conditions. Behavioral activities such as walking, object contacts, time spent in given zones, and entering the tunnels were measured. All the comparisons were made for two 3-min intervals, using a three-factor MANOVA, involving 2(sex)x2(subline)x8(3-mininterval). All subjects increased time spent in the tunnel zone, but RHA/Verh rats responded to a greater extent, especially the males. All subjects spent shorter times in the screen zone, but the RHA/Verh rats responded to a much greater extent. RHA/Verh rats, especially males responded with a substantial increase of time spent inside the tunnels. All subjects responded with an increased amount of object contacts. In general the RHA/Verh subjects showed a more pronounced response to novelty, as evidenced by a significant shift toward the tunnel zone. They spent more time in this zone than their RLA/Verh counterparts. Among the RLA/Verh rats, males tended to behave similarly to RHA/Verh rats, especially during the second 3min interval of session "12." The differences between the rat lines obtained in this study may be attributed to mechanisms specific to exploration, making them promising subjects to study the relationships between reactivity, novelty detection, adaptation, and environmental information processing.
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Uniaxial alignment of the columnar super-structure of a hexa (alkyl) hexa-peri-hexabenzocoronene on untreated glass by simple solution processing.
Uniaxially aligned, thin films of a discotic columnar thermotropic liquid crystalline material can be prepared by a simple solution zone-casting method, without the need for modified surfaces or traditional alignment techniques. Atomic force microscopy together with X-ray diffraction reveals single-crystalline-like order over several square centimeters, far exceeding the requirements for application of such films in organic molecular electronic devices such as field-effect transistors.
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