Molecular organization in perylene tetracarboxylic di-imide solid films

The vibrational spectra of thin solid films of three perylene tetracarboxylic di-imide derivatives (phenyl, methyl, and unsubstituted) are reported. A preferred molecular orientation in the evaporated solid films emerged for all three perylene derivatives from the i.r. data. Raman spectra obtained in resonance with the absorption band were characteristic of scattering via a Herzberg—Teller mechanism.     

Transition metal-coated nanoparticle films: vibrational characterization with surface-enhanced Raman scattering

The utilization of surface-attached gold nanoparticles as templates for generating Pt-group particles displaying near-optimal surface-enhanced Raman scattering (SERS) characteristics is described. Essentially epitaxial transition metal coatings down to the monolayer level can be prepared, most readily by the spontaneous replacement of an electrochemically deposited copper layer by the desired Pt-group metal. The and essentially pinhole-free nature of the coated nanoparticles is demonstrated from the form of the SER spectra for chemisorbed carbon monoxide and ethylene. The potential of the present strategy for synthesizing relatively monodispersed "core-shell" nanoparticles using a myriad of coating materials, also displaying SERS activity, is pointed out.     

Preparation and electronic characteristics of anionic perylene bisimide films

Neutral perylene bisimides(PBI) are well-known n-type organic semiconductors, with number of challenging electronic properties in their neutral and reduced states. We report the characteristic electronic properties of PBI anionic films. We unexpectedly discovered that pristine PBI dianion film showed p-type character, while oxidized dianion film(dominant neutral state with few radical anions) showed normal n-type semiconductor character based on Seebeck effect measurements. Both kinds of films exhibit high electrical conductivity with a potential for thermoelectric applications. The mechanism of polarity reversal is proposed.     

Optical and morphological characterization of bispyrazole thin films for gas sensing applications

The optical gas recognition capabilities of thin film layer of 4-[bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-amino]phenol deposed on quartz substrates were studied. The dynamic gas responses to the following analytes have been investigated as air pollutants (SO₂, NO₂, CO, CH₄ and NH₃). The spin-coated bispyrazole layer appears to have reversible response towards SO₂ and a very low and irreversible response to NO₂. The selectivity of the thin film based on bispyrazole layer with respect to other analytes was also examined and the present data show that the thin sensing layer in the presence of CO, CH₄ and NH₃ in low concentration does not influence its optical properties.     

Crystallographic and morphological characterization of thin pentacene films on polycrystalline copper surfaces

The degree of crystallinity, the structure and orientation of crystallites, and the morphology of thin pentacene films grown by vapor deposition in an ultrahigh vacuum environment on polycrystalline copper substrates have been investigated by x-ray diffraction and tapping-mode scanning force microscopy (TM-SFM). Depending on the substrate temperature during deposition, very different results are obtained: While at 77 K a long-range order is missing, the films become crystalline at elevated temperatures. From a high-resolution x-ray-diffraction profile analysis, the volume-weighted size of the crystallites perpendicular to the film surface could be determined. This size of the crystallites increases strongly upon changing temperature between room temperature and 333 K, at which point the size of individual crystallites typically exceeds 100 nm. In this temperature region, three different polymorphs are identified. The vast majority of crystallites have a fiber texture with the (001) net planes parallel to the substrate. In this geometry, the molecules are oriented standing up on the substrate (end-on arrangement). This alignment is remarkably different from that on single-crystalline metal surfaces, indicating that the growth is not epitaxial. Additionally, TM-SFM images show needlelike structures which suggest the presence of at least one additional orientation of crystallites (flat-on or edge-on). These results indicate that properties of thin crystalline pentacene films prepared on technologically relevant polycrystalline metal substrates for fast electronic applications may be compromised by the simultaneous presence of different local molecular aggregation states at all temperatures.     

Fabrication, characterization, and application in surface-enhanced Raman spectrum of assembled type-I collagen-silver nanoparticle multilayered films

In this paper, we report a facile method for the fabrication of type-I collagen-silver nanoparticles (Ag NPs) multilayered films by utilizing type-I collagen as a medium. These samples were characterized by UV-vis spectra photometer, atomic force microscopy, scanning electron microscopy, and Fourier transform IR spectrum. Experimental results show that collagen molecules serve as effective templates to assemble Ag NPs into multilayer films. These samples exhibit high surface-enhanced Raman scattering (SERS) enhancement abilities. For example, EF(nu(cc)) (EF means enhancement factor) at 1592 cm(-1) in the SERS spectrum of 4-aminothiophenol on seven-layered substrates was calculated to be 1.81 x 10(5), which is larger than that reported in several literatures. The EFs increased as the layer number of multilayer films increases.     

Molecular and morphological characterization of midblock‐sulfonated styrenic triblock copolymers

Midblock‐sulfonated triblock copolymers afford a desirable opportunity to generate network‐forming amphiphilic materials that are suitable for use in a wide range of emerging technologies as fuel‐cell, water‐desalination, ion‐exchange, photovoltaic, or electroactive membranes. Employing a previously reported synthetic strategy wherein poly(p‐tert‐butylstyrene) remains unreactive, we have selectively sulfonated the styrenic midblock of a poly(p‐tert‐butylstyrene‐b‐styrene‐b‐p‐tert‐butylstyrene) (TST) triblock copolymer to different extents. Comparison of the resulting sulfonated copolymers with results from our prior study provides favorable quantitative agreement and suggests that a shortened reaction time is advantageous. An ongoing challenge regarding the morphological development of charged block copolymers is the competition between microphase separation of the incompatible blocks and physical cross‐linking of ionic clusters, with the latter often hindering the former. Here, we expose the sulfonated TST copolymers to solvent‐vapor annealing to promote nanostructural refinement. The effect of such annealing on morphological characteristics, as well as on molecular free volume, is explored. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 490–497     

Molecular assemblies of perylene bisimide dyes in water

Perylene bisimides are among the most valuable functional dyes and have numerous potential applications. As a result of their chemical robustness, photostability, and outstanding optical and electronic properties, these dyes have been applied as pigments, fluorescence sensors, and n‐semiconductors in organic electronics and photovoltaics. Moreover, the extended quadrupolar π system of this class of dyes has facilitated the construction of numerous supramolecular architectures with fascinating photophysical properties. However, the supramolecular approach to the formation of perylene bisimide aggregates has been restricted mostly to organic media. Pleasingly, considerable progress has been made in the last few years in developing water‐soluble perylene bisimides and their application in aqueous media. This Review provides an up‐to‐date overview on the self‐assembly of perylene bisimides through π–π interactions in aqueous media. Synthetic strategies for the preparation of water‐soluble perylene bisimides and the influence of water on the π–π stacking of perylene bisimides as well as the resulting applications are discussed.     

Fabrication and characterization of homogeneous surface-enhanced Raman scattering substrates by single pulse UV-laser treatment of gold and silver films

The fabrication of SERS-active substrates, which offer high enhancement factors as well as spatially homogeneous distribution of the enhancement, plays an important role in the expansion of surface-enhanced Raman scattering (SERS) spectroscopy to a powerful, quantitative, and noninvasive measurement technique for analytical applications. In this paper, a novel method for the fabrication of SERS-active substrates by laser treatment of 20, 40, and 60 nm thick gold and of 40 nm thick silver films supported on quartz glass is presented. Single 308 nm UV-laser pulses were applied to melt the thin gold and silver films. During the cooling process of the noble metal, particles were formed. The particle size and density were imaged by atomic force microscopy. By varying the fluence, the size of the particles can be controlled. The enhancement factors of the nanostructures were determined by recording self-assembled monolayers of benzenethiol. The intensity of the SERS signal from benzenethiol is correlated to the mean particle size and thus to the fluence. Enhancement factors up to 10(6) with a high reproducibility were reached. Finally we have analyzed the temperature dependence of the SERS effect by recording the intensity of benzenethiol vibrations from 300 to 120 K. The temperature dependence of the SERS effect is discussed with regard to the metal properties.     

Surface enhanced resonance Raman scattering imaging of Langmuir-Blodgett monolayers of bis (benzimidazo) thioperylene.

The synthesis, spectroscopic characterization and surface-enhanced spectroscopy of a new electro active organic material bis (benzimidazo) thioperylene (Monothio BZP) are reported. Langmuir monolayers of Monothio BZP were successfully formed on water subphase and characterized by the pi-A surface-pressure area isotherm. Langmuir-Blodgett (LB) monomolecular layers of Monothio BZP were fabricated onto glass substrates and onto silver island films for surface-enhanced spectroscopic studies. The results of surface-enhanced resonance Raman scattering (SERRS), SERRS imaging and surface-enhanced fluorescence (SEF) studies for Monothio BZP LB monolayers are reported. Raman imaging (global imaging and point-by-point mapping) of the SERRS signal for a single monomolecular layer on silver islands were obtained using the 514.5 nm laser line. The SERRS imaging permits a visualization of the variation of the SERRS intensity across of the rough metal surface. The SEF was recorded for the excimer emission of aggregates in the LB film. The distance dependence and the enhancement factor of SEF were determined using fatty acid spacing layers. A temperature dependence study of the LB monolayer SERRS and SEF spectra was carried out between -190 degrees and + 200 degrees C confirming the thermal stability of the LB monolayer on silver. The specificity and the sensitivity of SERRS signal on metal island films was probed using mixed LB films with 0.01% molecular ratio of Monothio BZP in Arachidic Acid (AA). The micro-Raman SERRS spectra from ca. 10(-3) attomole of the dye were recorded.     

Optical, morphological and structural characterization of Langmuir-Schaefer films of a functionalized copper phthalocyanine

Langmuir-Schaefer (LS) films of copper(II) tetrakis-(isoprpoxy-carbonyl)-phthalocyanine (TiPCuPc) have been deposited onto various solid supports. Its floating film have been characterized at the air-water interface by means of Brewster Angle Microscopy and Langmuir curves. Vibrational modes of multilayer transferred LS film have been studied by Raman spectroscopy and the optical parameters (refractive index n and extinction coefficient k) have been determined in the visible range of the electromagnetic spectrum. Linearly polarized light absorbance measurements have been performed at room temperature in the 400-800 nm spectral range and the average orientation of the phthalocyanine rings have been estimated. Transmission electron microscopy has been also used to characterize the morphological properties of the LS film and a close packed arrangement of the deposited molecules has been observed.     

Energy transfer in molecular layer-by-layer films of water-soluble perylene diimides

Multilayer films of water-soluble anionic and cationic perylene diimide (PDI) moieties have been prepared using the molecular layer-by-layer method described in an earlier publication (Tang, T. J.; Qu, J. Q.; Müllen, K.; Webber, S. E. Langmuir 2006, 22, 26-28) and the fluorescence intensity compared with and without a base layer prepared using an anionic terrylene diimide dye (n-TDI), which serves as an energy-trapping layer for the PDI exciton. The fluorescence quenching data could be fit equally well to a modification of a model used by Kuhn to describe energy transfer from a J aggregate or a model developed by Kenkre and Wong to describe excitonic transfer. For both models, we obtain a characteristic energy-transfer distance on the order of 5.4 nm. Fluorescence quenching of the PDI via a single F?rster energy-transfer step to the n-TDI layer is ruled out on the basis of the observed power-law dependence. We also consider a model in which the excitation is trapped at the outermost surface. This model provides a reasonable fit to the data only if the Kuhn relationship is used.     

Bioaerosol detection and characterization by surface-enhanced Raman spectroscopy

Instrumentation has been developed to detect and characterize airborne pollen and bacteria rapidly by injecting a bioaerosol into a nanocolloidal suspension of silver particles using a micropump. The biological particles were mixed with the silver colloid in order to deposit the metallic particles on the surface of the bioanalyte. The silver/bioanalyte suspension was pumped through a light scattering cuvette, and the enhanced Raman spectrum was recorded. Surface-enhanced Raman spectra are presented for tree pollen (cottonwood and redwood pollen) and a bacterium (Escherichia coli), and the E. coli spectra are compared with results obtained from the literature and with results obtained previously by mixing various concentrations of the bioanalyte with the silver colloid. Although the system has not been optimized to maximize the Raman spectra, it is shown spectra can be obtained rapidly. Some assignments of the chemical bonds associated with the spectra are based on previously published results for bacteria and pollen.     

Molecular probes of solvation phenomena

The properties of the molecules present in any chemical or biological system are dependent on interactions with the environment, and a quantitative understanding of solvation phenomena remains a major challenge. Molecular recognition probes provide a new approach to quantitatively measure the properties of solvents. Traditionally, solvent polarity scales have been based on spectroscopic probes that provide insight into the nature of solvent-solute interactions. This review compares the solvent polarity parameters obtained from the wavelengths of UV/Visible absorption maxima with solute H-bond parameters obtained from the free energies of solution equilibria. The similarity of the solvent and solute H-bond scales leads to a general H-bond scale that uses the same parameters to describe both solvent and solute. The general H-bond scale provides a framework for understanding the relationship between local intermolecular interactions and the properties of the bulk medium. Intermolecular interactions are sensitive to solvation equilibria, so molecular recognition probes provide fundamentally different information from spectroscopic probes that are sensitive to the populations of different solvation states of the solute. Studies of mixed solvents demonstrate the potential of molecular recognition probes for providing new insights into solvation phenomena.     

Preparation and characterization of regioisomerically pure 1,7-disubstituted perylene bisimide dyes

A detailed study on bromination and subsequent imidization of perylene bisanhydride with cyclohexylamine is reported. The present results reveal that previously reported 1,7-difunctionalized perylene bisimides are presumably contaminated with the respective 1,6 regioisomers. N,N'-Dicyclohexyl-1,7-dibromoperylene bisimide 1,7-3 is obtained for the first time in isomerically pure form, and its structure is unequivocally confirmed by X-ray analysis. By using regioisomerically pure 1,7-dibromoperylene bisimide 1,7-3, 1,7-dipyrrolidinylperylene bisimides 4a-c and 1,7-dipyrrolidinylperylene bisanhydride 5 as well as the unsymmetrically difunctionalized 1-bromo-7-pyrrolidinyl- and 1-cyano-7-pyrrolidinylperylene bisimides 7 and 8 are synthesized in good yield.     

Single molecule study of perylene orange photobleaching in thin sol-gel films

The paper reports on photobleaching mechanisms of perylene orange embedded in thin sol-gel films, derived from single molecule studies. The experimental configuration uses wide-field illumination and one photon excitation of the molecules. Measurements have been performed both at ambient conditions and under vacuum in order to get information on the influence of oxygen on photobleaching in such porous samples. We have also recorded the evolution of photobleaching with respect to the excitation intensity. The results demonstrate that photobleaching from excited states higher than the first singlet and triplet states has a nonnegligible contribution as soon as the excitation energy exceeds a few hundred W/cm2 and that this process is favored in the presence of air. The study also demonstrates that perylene orange in sol-gel films is not a very efficient emitter but that photobleaching can be slow, which explains the interest for perylene orange as a good candidate to produce long lifetime solid-state lasers when embedded in monoliths of sol-gel.     

Gas-sensor properties of composite semiconductor films of substituted perylene and tin dioxide nanoparticles

Electrical conductivity of film samples of a composite constituted by a perylene derivative (3,4,9,10-perylenetetracarboxylic-dianhydride) and SnO₂ nanoparticles was studied in adsorption of vapors of ammonia, toluene, aqueous hydrogen peroxide, ethanol, and water. A model of formation of the composite sample under study and a mechanism by which adsorbed molecules affect its electrical conductivity are suggested.     

Water-soluble perylene diimides: Solution photophysics and layer-by-layer incorporation into polyelectrolyte films

Recently the synthesis of water-soluble and fluorescent perylene diimides has been reported (Müllen, K.; et al. Angew. Chem., Int. Ed. 2004, 43, 1528; Chem.-Eur. J. 2004, 10, 5297). We have characterized the photophysics of two of these compounds (anionic n-PDI, CAS Reg. No. 694438-88-5. and cationic p-PDI, CAS Reg. No. 817207-4-7) in pure water, dimethyl sulfoxide (DMSO), and aqueous NaCl. These studies, supported by molecular dynamics simulations, have led to the conclusion that these compounds form weakly interacting aggregated species in pure water. n-PDI and p-PDI have been incorporated in polyelectrolyte films of poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDAC) following the layer-by-layer (LBL) methodology. The optical density and fluorescence intensity of the PDI-LBL films grew linearly with the number of layers, and the PDI was not extracted by subsequent polyelectrolyte deposition. The PDI fluorescence quantum yield was substantially diminished in these films, which we interpret as a self-quenching effect, enhanced by inter- and intralayer energy transfer. Energy-transfer studies to the incorporated cationic dye Brilliant Green (BG) has demonstrated that the BG resides in the same PSS-rich region as p-PDI and is largely excluded from the region that contains n-PDI (PDAC-rich).     

Solid-state detection of gases by use of thin films based on pyrazole units, and morphological characterization of the films by AFM

Synthesis of a series of heterocyclic compounds based on pyrazole units is reported. The possibility of using these compounds, as solid-state thin layers deposited on quartz substrates, for optical recognition of hazardous pollutant gases was investigated. The gases SO₂, NO₂, CO, CH₄, and NH₃ were studied. Two of the ligand layers had reversible sensitivity toward SO₂, with good reaction time. The presence of CO, CH₄ NO₂, and NH₃ had no effect on the optical properties. Morphological characterization by use of AFM microscopy was also investigated.     

Modulation of the optical response of polyethylene films containing luminescent perylene chromophores

In this work, two perylene derivatives containing different peripheral alkyl chains (i.e., N,N'-bis-(hexyl)perylene-3,4,9,10-tetracarboxyldiimide (ES-PTCDI) and N,N'-bis-(2'-ethylhexyl)perylene-3,4,9,10-tetracarboxyldiimide (EE-PTCDI)) were synthesized and efficiently dispersed at low loadings (from 0.01 to 0.1 wt %) into linear low-density polyethylene (LLDPE) by processing in the melt. Spectroscopic investigations (UV-vis and fluorescence) combined with quantum-mechanical studies demonstrated the ability of both chromophores to generate aggregates among the planar structure of dyes when dissolved in solution or dispersed into LLDPE above a certain concentration. The data acquired for dyes' dispersions into the polymer matrix reveal that the optical properties and responsiveness to mechanical stimuli are strongly dependent on the compactness of perylene aggregates provided by the different molecular structure of dyes. In particular, the strong intermolecular aggregates of ES-PTCDI resulted in being more resistant toward mechanical stress and less orientable by uniaxial drawing along the drawing direction of the film, whereas the less compact and distorted supramolecular architecture of EE-PTCDI chromophores provided composite films with a remarkable optical response to mechanical solicitations.