Showing papers in "Molecular Crystals and Liquid Crystals in 2004"
TL;DR: A series of new compounds o-n-hydroxy-p-nhexadecanoyloxybenzylideneaniline and its substituted derivatives was synthesized from the esterification of palmitic acid with intermediary Schiff bases, which posssess various terminal substituents X (X = H, F, Cl, Br, OCH3, CH3, and C2H5) as discussed by the authors.
Abstract: A series of new compounds o-n-hydroxy-p-n-hexadecanoyloxybenzylideneaniline and its substituted derivatives was synthesized from the esterification of palmitic acid with intermediary Schiff bases, which posssess various terminal substituents X (X = H, F, Cl, Br, OCH3, CH3, and C2H5). All compounds possess mesomorphic properties wherein compounds with X = H, F, Cl, Br, and OCH3 exhibit smectic A (SmA) phases and those with terminal substituents CH3 and C2H5 are monotropic liquid crystals showing smectic C phases (SmC). Correlation studies of the clearing temperature (Tc) of the title compounds and polarizability related to mesophase stability and molecular anisotropy are reported.
77 citations
TL;DR: In this paper, the ultraviolet stability of several high birefringence liquid crystal structures was studied and it was shown that compounds containing carbon-carbon double bond or triple bond are less stable than those containing merely phenyl rings.
Abstract: The ultraviolet stability of several high birefringence liquid crystal structures was studied. Compounds containing carbon-carbon double bond or triple bond are less stable than those containing merely phenyl rings. In addition to the structural effect, absorption wavelength also plays an important role to the degradation mechanisms.
55 citations
TL;DR: In this article, a series of achiral non-symmetric banana-shaped compounds were synthesized and some of them were found to exhibit a nematic phase composed of the bent molecule.
Abstract: We synthesized a series of achiral non-symmetric banana-shaped compounds. Some of them were found to exhibit a nematic phase. We are strongly interested in this nematic phase composed of the bent molecule. On the basis of the assumption that the dynamics of the nematic phase of the banana-shaped molecules could be much different from the conventional thermotropic nematic phase of the rod-like molecules, we carried out the dynamic light scattering measurement. And we will present the unique phase behaviour of newly synthesised non-symmetric banana-shaped material with dichloro-substituted mesogen.
54 citations
TL;DR: In this article, the photooptic effect in induced cholesteric mixtures using photosensitive nematic host has been observed, and the changes of the pitch (color) and optical anisotropy (Δn) and also cholesterolic-isotropic phase transition have been studied.
Abstract: For the first time the photooptic effect in induced cholesteric mixtures using photosensitive nematic host has been observed. The changes of the pitch (color) and optical anisotropy (Δn) and also cholesteric-isotropic phase transition have been studied. Potential applications of these systems are color filters, UV image recording, UV sensors, and optical data processing systems.
46 citations
TL;DR: The mesogenic and optical properties of few families of nematic liquid crystals with low, medium and high birefringence as well as high tilted chiral anticlinic(antiferroelectric)smectics recently developed have been shortly characterized and reviewed as discussed by the authors.
Abstract: The mesogenic and optical properties of few families of nematic liquid crystals with low, medium and high birefringence as well as high tilted chiral anticlinic(antiferroelectric)smectics recently developed have been shortly characterized and reviewed. They are:alkyl 4-trans-(4-trans-alkylcyclohexyl)cyclohexyl carbonates being liquid crystals with ordinary index nolower than silica glass in broad temperature range,high birefringence two ring 4′-alkyl- and 4′-alkoxy-4′-isothiocyanatotolanes and three ring 4′-(4-alkyl)phenyl-, 4′-(trans-4-alkyl)cyclohexyl- or 4-(4′-trans-alkyl)cyclohexylethyl-4-isothiocyanatotolanes unsubstituted or laterally substituted by fluorine or chlorine atoms,(S)1-methylheptyloxyphenyl 4-(perfluoroalkanoyloxyalkoxy)biphenylates and(S)1-methylheptyloxybiphenylyl-4-yl 4-(perfluoroalkanoyloxyalkoxy)benzoates having the broad temperature range of antiferroelectric phase.The examples of mixtures with low noandΔn, highΔn as well as orthoconic antiferroelectric mixtures are given.
46 citations
TL;DR: Several dicationic salts with bis(triflimide) as counterions were prepared by metathesis reaction of the corresponding viologen dibromides (diiodides) with lithium triflimides in a polar solvent as discussed by the authors.
Abstract: Several dicationic salts with bis(triflimide) as counterions—otherwise known as viologens—were prepared by metathesis reaction of the corresponding viologen dibromides (diiodides) with lithium triflimide in a polar solvent. They were characterized for their thermotropic liquid-crystalline properties with various experimental techniques. Two of them had low crystal-to-smectic phase transitions (Tm) at –4 and 28°C; the other two also had low Tm values, at 51 and 58°C. Each had a wide range of LC phase. Two had relatively low crystal-to-isotropic (Tm) transitions at 117 and 131°C. Each had excellent thermal stability in the temperature range of 327–396°C. They exhibited photoluminescence property in both nonpolar and polar solvents as well as in the solid state. Their emission spectra in the solid state exhibited hypsochromic shift when compared with those in solution of dimethoxyethane.
45 citations
TL;DR: Anisotropic ion-conductive materials have been prepared by self-assembly of a conventional ionic liquid and a hydroxyl-terminated liquid crystal on the nanometer scale.
Abstract: Anisotropic ion-conductive materials have been prepared by self-assembly of a conventional ionic liquid and a hydroxyl-terminated liquid crystal. These assemblies form phase-segregated layered structures on the nanometer scale. Anisotropic ionic conductivities along the direction parallel and perpendicular to the layer have been successfully measured for the sample forming oriented monodomains. The ionic conductivity parallel to the layer (σi//) is higher than that perpendicular to the layer (σi⊥). The maximal anisotropy (σi///σi⊥) is 2.6 × 103 at 37°C in the smectic B phase.
45 citations
TL;DR: In this paper, the authors describe properties of two solid-state electrochromic devices with a WO3/natural polymer-based electrolyte/CeO2-TiO2 configuration.
Abstract: Solid-state electrochromic devices(ECDs)are of considerable technological and commercial interest because of their controllable transmission, absorption, and/or reflectance. For instance, a major application of these devices is in smart windows that can regulate the solar gains of buildings and also in glare attenuation in automobile rear view mirrors. A typical electrochromic device has a five-layer structure: GS/TC/EC/IC/IS/TC/GS, where GS is a glass substrate, TC is a transparent conductor, usually ITO(indium tin oxide)or FTO(fluorine tin oxide), EC is an electrochromic coating(typically WO3, Nb2O5, Nb2O5:Li+or Nb2O5–TiO2), IC is an ion conductor(solid or liquid electrolyte), in our case polymeric films based on natural polymers like starch or cellulose, and IS is an ion storage coating(typically CeO2–TiO2, CeO2–ZrO2, or CeO2–TiO2–ZrO2).This paper describes properties of two electrochromic devices with a WO3/natural-polymer-based electrolyte/CeO2–TiO2configuration.
40 citations
TL;DR: In this paper, the relationship between chemistry, properties, and performance of natural fibers is investigated and a new generation of value added composites that will be performance driven and durable is proposed.
Abstract: One of the advantages of using natural fibers in composites is that they are biodegradable and renewable. Many applications for composites, however, require high performance and durability. While our attention is being drawn to renewable, biodegradable and sustainable resources for materials, we are faced with the concern about durability. For the most part, we have designed and used natural fiber-based composites accepting performance limitations such as dimensional instability, ultraviolet and biological degradation, and thermal instability. However, with a better understanding the relationship between chemistry, properties, and performance of natural fibers, we can produce a new generation of value added composites that will be performance driven and durable.Properties such as dimensional instability, flammability, biodegradability, and degradation caused by acids, bases, and ultraviolet radiation are all a result of chemical degradation reactions(hydrolysis, oxidation, dehydration, and reduction)which...
34 citations
TL;DR: The terahertz (THz) refractive indices of a liquid crystal 4′-n-pentyl-4cyanobiphenyl (5CB) in both of the nematic and isotropic phases were determined in this article.
Abstract: The terahertz (THz) refractive indices of a liquid crystal 4′-n-pentyl-4cyanobiphenyl (5CB) in both of the nematic and isotropic phases were determined by terahertz (THz) time-domain spectroscopy for the first time, to our knowledge. We find that the extinction coefficient of 5CB is negligibly small in this frequency range. The birefringence of 5CB, on the other hand, is as large as 0.2. This is comparable to that of 5CB in the visible and near IR. The experimental results indicate that liquid crystals are potentially useful for device applications in the THz frequency range.
34 citations
TL;DR: In this article, near the reentrant isotropic (IRE) and Discotic Nems (ND) phase transitions in a lyotropic mixture of potassium laurate, decanol, and D2O were investigated.
Abstract: Lyotropic nematic textures are investigated, by image processing, near the reentrant isotropic (IRE)–discotic nematic (ND)–biaxial nematic (NB)–clamitic nematic (NC)–isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol, and D2O. The (NB), intermediate phase between the two uniaxial nematic ones, is characterized by optical birefringence measurements and discussed in terms of structural changes in the image frame by means of an adequate statistical approach. PACS: 61.30.-v, 64.70.Md, 42.65.Jx
TL;DR: In this paper, the effect of photo-induced optical anisotropy in thin polyvinyl-cinnamate (PVCi) derivatives was investigated and shown to be due to reversible photophysical reorientation of the chromophore groups, which accumulates photochemical nonactive part of the UV-light energy.
Abstract: The effect of LC photo-aligning by poly(vinyl-cinnamate) (PVCi) derivatives is consequent to the phenomena of the photo-induced optical anisotropy, found in PVCi films during their illumination by UV-light within the self-absorption band of the PVCi film. We proved in our experiment, that the phenomena of the photo-induced birefringence in thin films of PVC derivatives takes place due to the two main factors: described earlier irreversible photochemical process (2 + 2) cycloaddition of cinnamoyl groups and reversible photophysical reorientation of the chromophore groups, that accumulates photochemical non-active part of the UV-light energy. We reviewed various applications of the effect of photo-induced optical anisotropy in PVCi films including: writing the polarization holograms and images, optical data processing, development of different polarization optical elements, non-destructive testing of defects, LC photo-aligning. Most of the early papers, devoted to the above mentioned applications were publi...
TL;DR: In this paper, it was found that doping of tiny ferroelectric particles to a nematic liquid crystal (LC)strongly affects dielectric properties of the system, and that the doping increases dielectionric response of the LC due to interaction between LC molecules and particles, which possess large dipole moment and high polarisability.
Abstract: It was found that doping of tiny ferroelectric particles to a nematic liquid crystal(LC)strongly affects dielectric properties of the system. The doping increases dielectric response of the LC due to interaction between LC molecules and particles, which possess large dipole moment and high polarisability. The suspension reveals high dielectric response on either side of the Curie temperature, TCurie, and peculiarity at the vicinity of TCurie. This result points at retention of dipole ordering above Curie temperature that may be a result of a memory effect.
TL;DR: In this article, the conjugated-bond pattern along single polyacetylene chains was found to show temperature-independent Zener-type tunnelling at low temperatures, and at higher temperatures, the current shows a strong increase with temperature and the nonlinearity of the currentvoltage characteristics decreases.
Abstract: The preparation of individual polyacetylene nanofibres has allowed a more probing investigation of the properties of polyacetylene. A significant discovery is that at low temperatures, polyacetylene nanofibres show temperature-independent Zener-type tunnelling, that we suggest is tunnelling of the conjugated-bond pattern along single polyacetylene chains. At higher temperatures, the current shows a strong increase with temperature and the nonlinearity of the current-voltage characteristics decreases. We make a comparison with similar behaviour found in single-wall carbon nanotube networks, and show that the decrease in nonlinearity is consistent with our generic calculations for fluctuation-assisted tunnelling and thermal excitation. There is no evidence for superconductivity in resistance measurements on polyacetylene. The thermoelectric power of polyacetylene and other bulk organic conducting polymers indicates the absence of significant superconductivity arising from the conventional electron-phonon me...
TL;DR: In this article, the synthesis, characterization and mesomorphic properties of a new type of discotic liquid crystalline dimer bearing an electronrich triphenylene discotic connected to an electron-deficient anthraquinone discotic via an alkyl chain spacer are reported.
Abstract: The synthesis, characterization and mesomorphic properties of a new type of discotic liquid crystalline dimer bearing an electron-rich triphenylene discotic connected to an electron-deficient anthraquinone discotic via an alkyl chain spacer are reported. This donor-sigma-acceptor type molecule displays a columnar mesophase over a wide temperature range.
TL;DR: The convergent synthesis of new symmetrical and non-symmetrical star-shaped mesogens based on a phloroglucinol core is presented in this paper, where molecules with three different arms were derived via esterification of various 4-benzoylbenzoic acid derivatives, substituted with polar groups and n alkoxy chains.
Abstract: The convergent synthesis of new symmetrical and non-symmetrical star-shaped mesogens based on a phloroglucinol core is presented. Molecules with three different arms were derived via esterification of various 4-benzoylbenzoic acid derivatives, substituted with polar groups and n alkoxy chains (n = 1–3), by using a combination of protecting group techniques and stoichiometric reactions. The thermotropic properties were investigated by differential scanning calorimetry, polarised optical microscopy and synchrotron X-ray diffraction. It is found that molecules with more than seven lateral chains form mesophases. The presence of strong polar groups (−NO2) enlarges the temperature range of the liquid crystal phase. For all studied materials the diffractograms can be indexed according to a two-dimensional hexagonal lattice. The lattice parameters indicate that the flexible chains are interdigitated.
TL;DR: In this article, the authors synthesized dialkylterthiophene derivatives ω-substituted with cyclohexylethyl moiety, which exhibit smectic mesophases at room temperature, and investigated their charge carrier transport properties.
Abstract: We synthesized dialkylterthiophene derivatives ω-substituted with cyclohexylethyl moiety, which exhibit smectic mesophases at room temperature, and investigated their charge carrier transport properties. In particular, trans-pentylcyclohexylethyl-propylterthiophene (3-TTP-C2CH-5) held SmB phase at room temperature. Furthermore, a 3:1 mixture of 3-TTP-C2CH-5 and (2-methylbutyl)-dodecylterthiophene (5∗-TTP-12) showed the SmB phase between 101°C and −15°C, and the highly ordered smectic phase below −15°C. In the SmB phase of the mixture, hole and electron mobility was 10−3 cm2/Vs, and independent of temperature and electric field over room temperature. However, below room temperature, the mobility depended on both temperature and electric field, as is often observed in organic amorphous solids and formarized by Gaussian disorder model, suggesting that the carrier transport in the smectic mesophase can be explained by the hopping conduction in disordered molecular sites.
TL;DR: In this paper, the synthesis and characterization of a side group polymer based on a predominantly poly(ethylene oxide) backbone to which are attached triphenylene-based mesogenic groups via flexible spacers is reported.
Abstract: The synthesis and characterization is reported of a novel discotic side group polymer based on a predominantly poly(ethylene oxide) backbone to which are attached triphenylene-based mesogenic groups via flexible spacers. The thermal and mechanical behavior of this polymer and its complex with lithium perchlorate are compared. The addition of salt increased both the glass transition temperature and clearing point of the host polymer. The temperature dependence of the ionic conductivity of the polymer–salt complex is reported and reveals that ionic conduction can occur in essentially solid-like liquid crystal polymer electrolytes. Ion transport in this material presumably involves assistance from local segmental motions of the backbone but does not rely upon long range cooperative motions.
TL;DR: In this paper, the authors investigated the polarization phenomena in an elliptical liquid crystal-core fiber at third optical window, i.e., close to 1550 nm, and measured the polarization mode dispersion and the beat-length parameter.
Abstract: Polarization phenomena in an elliptical liquid crystal-core fiber at third optical window, i.e., close to 1550 nm have been investigated. This includes direct measurement of polarization mode dispersion and the beat-length parameter. The elliptical liquid crystal-core fiber contained a nematic mixture characterized by extremely low values of refractive indices.
TL;DR: A series of dodecyloxybiphenylyl and cholesteryl group containing dimers with ethers as spacers have been prepared and their liquid crystalline properties were investigated as a function of spacer length.
Abstract: A series of dodecyloxybiphenylyl and cholesteryl group containing dimers with ethers as spacers have been prepared and their liquid crystalline properties were investigated as a function of spacer length. For short spacers SmA and SmC phases were observed with monolayer ordering. This is aparent from polarization microscopy and temperature dependent X-ray measurements. With increasing spacer length a N∗-phase gradually appears whose liquid crystalline range increases. For the dodecyl spacer no smectic phase is observed anymore. For the nonyl spacer reentrant behavior is found (N∗-TGB-SmA-TGB-N∗). Reentrant behavior, probably N∗-TGB-N∗, is also observed for a related compound with an ester spacer.
TL;DR: In this paper, the authors study the dielectric properties of a dilute suspension of ferroelectric particles in a nematic liquid crystal (LC) host and propose theoretical model for the effective dielectrics function of the suspension.
Abstract: We study dielectric properties of a dilute suspension of ferroelectric particles in a nematic liquid crystal(LC)host. It is supposed that submicron particles do not disturb the LC alignment and the suspension macroscopically appears similar to a pure LC. We propose theoretical model for effective dielectric function of ferroelectric LC suspension. It is found that particles permanent polarisation may significantly increase the effective value of suspension dielectric function in comparison with pure LC. For more elongated particles depolarisation factor is smaller and respectively the contribution of induced polarisation of particles to the effective dielectric function is higher.
TL;DR: In this paper, the crystal structure and phonon dynamics of pentacene were computed with the quasi harmonic lattice dynamics (QHLD) method, based on atom-atom potential.
Abstract: The crystal structure and phonon dynamics of pentacene is computed with the Quasi Harmonic Lattice Dynamics(QHLD)method, based on atom-atom potential. We show that two crystalline phases of pentacene exist, rather similar in thermodynamic stability and in molecular density. The two phases can be easily distinguished by Raman spectroscopy in the 10–100 cm−1spectral region. We have not found any temperature induced phase transition, whereas a sluggish phase change to the denser phase is induced by pressure. The bandwidths of the two phases are slightly different. The charge carrier coupling to low-frequency phonons is calculated.
TL;DR: In this article, a fast optical modulator capable of switching large amount of optical retardation (a few microns) in less than 1ms was demonstrated by employing a dual frequency nematic in cells with high pre-tilt alignment and a special addressing scheme that features amplitude and frequency modulated voltage.
Abstract: We demonstrate a fast optical modulator capable of switching large amount of optical retardation (a few microns) in less than 1ms. The result is achieved by employing a dual frequency nematic in cells with high pre-tilt alignment and by providing a special addressing scheme that features amplitude and frequency modulated voltage. We explore the effect of surface alignment and dielectric heating on the switching time. We also report the measurements of dielectric permittivities and crossover frequency of dual frequency nematic.
TL;DR: In this article, the opportunities created by interfacing photonics with nanotechnology and biotechnology are discussed, including applications of quantum dots for bioimaging and of fluorescence labeled magnetic nanoparticles for multimodal imaging.
Abstract: Today major breakthroughs are more likely to occur in interdisciplinary areas. This paper discusses opportunities created by interfacing photonics with nanotechnology and biotechnology. Examples are provided from our work at the Institute for Lasers, Photonics and Biophotonics. Specifically discussed are applications of nanophotonics to nanomedicine, which is an emerging field utilizing nanostructures for bioimaging, biosensing and targeted therapy. Applications of quantum dots for bioimaging and of fluorescence labeled magnetic nanoparticles for multimodal imaging are presented. Use of nanoparticles for light-activated therapy, the photodynamic therapy, is discussed. Examples of nanophotonics to optically track and monitor nanoparticle delivery genes of and subsequent transfection is given. Finally, some examples of future opportunities are presented.
TL;DR: In this article, the behavior of a cholesteric mixture, consisting of the negative dielectric anisotropy liquid crystal MBBA and a chiral dopant S811(1%b.c.).
Abstract: We have investigated the behavior of a cholesteric mixture, consisting of the negative dielectric anisotropy liquid crystal MBBA and a chiral dopant S811(1%b.w.). In the phase diagram a.c. applied voltage versus confinement ratio, in addition to the transition previously observed, before reaching the domain of the transition TIC(Translationnary Invariant Cholesteric)–modulated TIC, we have observed a new stability domain for the topological bubble. These bubbles are now surrounded by the TIC domains and necessarily associated to an hyperbolic − 1 defect of the in plane director component.We have also obtained experimentally topological defect chains, formed by topological dipoles similar to the ones formed in 2 compound materials: liquid crystal/solid spheres or liquid crystal/liquid droplets.
TL;DR: In this paper, an ion LC-dendrimer was obtained by proton transfer reaction of alkanoic acid and primary amino groups of poly(amidoamine) dendrimers in a 1:1 molar ratio.
Abstract: Ionic LC-dendrimers were obtained by proton-transfer reaction of alkanoic acid and primary amino groups of poly(amidoamine) dendrimer in a 1:1 molar ratio. The ion complexes containing stearate, palmitate or myristate ions showed a smectic A phase. However, the ion complexes containing laurate and decanoate ions exhibited no liquid-crystalline phase. Oilystreak, maltese, and homeotropic textures were observed in the smectic A phase. The formation of the homeotropic structure is characterized by conoscopic observation. The X-ray diffraction pattern in the smectic A temperatures consists of sharp inner reflections at the small angles and the wide-angle diffuse halo. Mixtures of the dendrimer and stearic acid [a molar ratio (x) of stearic acid against the primary amino groups of the dendrimer] were prepared; mixtures with x = 0.11–1.5 showed a smectic A phase. However, the mixture with x = 2.33 formed a disordered hexagonal columnar mesophase, characterized by an optical texture and X-ray diffraction measure...
TL;DR: In this article, several compounds with high birefringence and having to have a high polarizability, isothiocyanato (NCS) terminal group was introduced.
Abstract: Several compounds with high birefringence and having tolane structure were synthesized. For a high polarizability, isothiocyanato (NCS) terminal group was introduced. Another goal of this study was reduction of melting point and smectic phases by introduction of fluorine as lateral substituent. The transition temperatures for all the synthesized compounds and the refractive and dielectric indices for one of the compounds have been determined. Electro-optic (EO) measurements were also performed.
TL;DR: In this article, the fundamental dielectric properties of nematic liquid crystals were measured in the 3-33 GHz frequency range for the purpose of applying liquid crystals to adaptive devices in the microwave and millimeter-wave ranges.
Abstract: The fundamental dielectric properties of nematic liquid crystals were measured in the 3–33 GHz frequency range for the purpose of applying liquid crystals to adaptive devices in the microwave and millimeter-wave ranges. We proposed two kinds of measurement methods. Firstly, we used the cut back method to determine the NLCs' permittivity and loss tangent, which is the first time it has been used for this purpose. Secondly, the dielectric permittivity of nematic liquid crystals used for the microstrip-line devices were determined in the 3–33 GHz frequency range by using a newly developed inductive coupled ring resonator. In addition, the effective alignment coefficient ηa(ηa < 1) is proposed for the determination of the effective $\varepsilon_{\,\parallel}^\prime$ (the long axis of the liquid crystal molecules is parallel to the direction of the r.f. electric field Erf) because the value of $\varepsilon_{\,\parallel}^\prime$ must be modified to $\eta_{\rm a}\varepsilon_{\,\parallel}^\prime$ in the microstri...
TL;DR: In this article, the authors synthesized low molar mass liquid crystals having imidazolium salt to investigate thermal properties and ionic conductivity, regardless of spacer length.
Abstract: We synthesized low molar mass liquid crystals having imidazolium salt to investigate thermal properties and ionic conductivity Two smectic (smectic A and smectic E) phases were shown for imidazolium salt derivatives, regardless of spacer length The ionic conductivity of imidazolium salt derivatives in the smectic E phase increased with increasing temperature The ionic conductivity of imidazolium salt derivatives was about 10−8–10−7 Scm−1 near room temperature The highest value of ionic conductivity for imidazolium salt derivatives was about 10−3 Scm−1 at 140°C
TL;DR: In this article, a two-layer photovoltaic cell with two organic layers was constructed and the hole-conducting layer consisted of a hexa-peri-hexabenzocoronene (HBC) derivative.
Abstract: We made photovoltaic cells containing two organic layers. The hole-conducting layer consists of a hexa-peri-hexabenzocoronene (HBC) derivative. The electron-conducting component is an alkylester of perylene tetracarboxylic acid. Both compounds form columnar mesophases which can provide 1D pathways for transport. The current/voltage-characteristics of the two-layer devices indicate a photovoltaic effect with an open circuit voltage of Voc ≈ 0.8 V, a short circuit current of Isc ≈ 3.9 μA/cm2, and a filling factor of FF ≤ 31%. The spectral distribution of the photocurrent of different samples indicates that excitations of the perylene derivative or of the HBC derivative both can lead to a photovoltaic effect.