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Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3rd order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor–Acceptor–Donor (D–A–D) architecture with acceptor, AcacBF2, located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert–Mataga plot. As donor strength in the D–A–D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.

An important virtue of polymer-based electronic devices is solution processing that offers large area, cheap roll-to-roll manufacturing. However, all organic electronic devices require a multilayered structure of successive thin layers stacked one on top of the other with defined interfaces and little to no layer intermixing. Solution processing of this type of structure is challenging, requiring careful formulation of the solution and selection of solvents, and is often avoided by turning to molecular films that are deposited by complicated and energy consuming deposition processes. Therefore, self-forming interlayers, where molecules segregate from the semiconducting layer to spontaneously form a distinct thin layer, show great potential for fast and simple processing of polymer-based devices. Until now, self-forming interlayers were demonstrated as a tool to tune the energy-level alignment at either the top or bottom interface in organic devices. Here we show that two judiciously selected additives can be collectively mixed into the active layer blend and each spontaneously migrates to a different interface to self-form interlayers at both organic/contact interfaces. The driving forces for additive migration, surface and interface energy considerations, induce interlayer formation during spin coating and top electrode deposition. Both interlayers modify the interfacial energy level alignment leading to improved device performance. In this case we show that a tri-layer stack composed of electron selective layer/active layer/hole selective layer is formed in one spin coating process. The methodology demonstrated here for organic solar cells is general and versatile, suitable for all polymer electronic devices and can be translated to roll-to-roll fabrication processes such as printing and coating.

We report on the modulation of the electrical properties of graphene-based transistors that mirror the properties of a few nanometers thick layer made of dipolar molecules sandwiched in between the 2D material and the SiO2 dielectric substrate. The chemical composition of the films of quinonemonoimine zwitterion molecules adsorbed onto SiO2 has been explored by means of X-ray photoemission and mass spectroscopy. Graphene-based devices are then fabricated by transferring the 2D material onto the molecular film, followed by the deposition of top source-drain electrodes. The degree of supramolecular order in disordered films of dipolar molecules was found to be partially improved as a result of the electric field at low temperatures, as revealed by the emergence of hysteresis in the transfer curves of the transistors. The use of molecules from the same family, which are suitably designed to interact with the dielectric surface, results in the disappearance of the hysteresis. DFT calculations confirm that the dressing of the molecules by an external electric field exhibits multiple minimal energy landscapes that explain the thermally stabilized capacitive coupling observed. This study demonstrates that the design and exploitation of ad hoc molecules as an interlayer between a dielectric substrate and graphene represents a powerful tool for tuning the electrical properties of the 2D material. Conversely, graphene can be used as an indicator of the stability of molecular layers, by providing insight into the energetics of ordering of dipolar molecules under the effect of electrical gating.

Molecular films of quinonoid zwitterions, of the general formula C6H2([horiz bar, triple dot above]O)2([horiz bar, triple dot above]NHR)2, have been shown to display electronic properties highly dependent on the nature of the N-substituent R when deposited on gold substrates. The different spacing and organization of the molecules can lead to molecular films with semi-metal or dielectric behavior. With the long term goal to establish how packing effects in the solid state correlate with properties as thin films, we first attempted to identify by X-ray diffraction analysis candidate molecules showing suitable packing arrangements in the crystalline state. To this end, we have prepared a series of new functionalized, enantiopure or sterically-hindered quinonoid zwitterions and established the crystal structure of those with R = CH2–CH2–Ph (6), CH2–CH2–CH2–Ph (7), CH2–CH2–CH2–CH2–Ph (8), CH2–CH2–CH(Ph)–Ph (9), CH(CH3)–Ph (12), CH(CH2–CH3)–Ph (13), CH2–((4–CH3)–C6H4) (15), CH2–((4–NH2)–C6H4) (19) and CH2–CH2–((3,4–(OCH3)2)–C6H3) (24). An analysis of the crystal packing of three molecules, 5, 13 and 15, selected as illustrative examples for comparisons, was carried out and it was unexpectedly found that these chemically very similar molecules gave rise to different packing in the bulk, with resulting thin films showing different electronic properties. Various methods have been used for the characterization of the films, such as synchrotron radiation-based FTIR spatial spectra-microscopy, which provided an anchoring map of zwitterion 15 on a patterned substrate (Au/SiO2) showing its selective anchoring on gold. This is one of the best examples of preferential anchoring of a zwitterion and the sole example of spatial localization for a quinonoid zwitterion thin film. We have also used combined photoemission and inverse photoemission spectra and the data were compared to occupied and unoccupied DFT density state calculations.

We demonstrate the efficient formation of carbon–nitrogen bonds starting from CH4 and NH3 on a metal surface at cryogenic temperatures. Electrons in the energy range of 1–90 eV are used to initiate chemical reactions in mixed molecular films of CH4 and NH3 at ∼15 K, and the products are detected by performing temperature programmed desorption (TPD). Extensive dehydrogenation occurs at all energies giving the products CH2NH and HCN in preference to CH3NH2. This is likely to do with the energetics of the reactions and the subsequent stability of these species in the condensed film. Thermal processing of the irradiated mixture favours dehydrogenation as indicated by the results of using different desorption rates. Electron impact excitation and subsequent dissociation into radicals is the reaction-initiating step rather than ionization of CH4 and NH3, as inferred from the yield of products as a function of electron energy. This could give insight into the important catalytic process of the industrial scale synthesis of HCN from CH4 and NH3 over Pt. This may also be a relevant pathway in the astrochemical environment where CN and HCN are abundant and low-energy electrons are found ubiquitously.

Covalently-assembled monolayers of functionalized Zn-porphyrin complex (5,10,15,20-tetra(4-pyridyl)-porphyrin, Zn-TPyP) are employed as the template layer for fabricating heterogeneous molecular dyads composed of opto-active metallo-terpyridyl complexes on SiOx substrates. Metallo-linkers such as Cu2+ and Pd2+ are exploited to connect the Zn-porphyrin template layer with the metallo-terpyridyl complexes (M–PT, M = Fe2+, Ru2+, Os2+, while PT = 4′-pyridyl terpyridyl) using a wet chemical “layer-by-layer” (LBL) technique. Formation of both the template and dyad layers over the SiOx substrates were probed by atomic force microscopy (AFM) and UV-vis absorption techniques. The molecular films were used for comparison and to study the effect of different metallo-linkers based on the changes in the characteristics of the Soret bands of Zn-TPyP and the metal-to-ligand charge-transfer (MLCT) bands of terpyridyl complexes. Besides, detailed electronic structure calculations based on first-principles density functional theory (DFT) and time-dependent DFT (TDDFT) have been performed for understanding experimentally observed photophysical properties of the surface-confined dyads.

Well-ordered molecular films play an important role in nanotechnology, from device fabrication to surface patterning. Self-assembled monolayers (SAMs) of 6-mercaptopurine (6MP) on the Au(100)-(1 × 1) and Au(111)-(1 × 1) have been used to understand the interplay of molecule-substrate interactions for heterocyclic thiols capable of binding to the surface by two anchors, which spontaneously form a highly disordered film on Au(111). Our results reveal that for the same surface coverage the simple change of the substrate from Au(111)-(1 × 1) to Au(100)-(1 × 1) eliminates molecular disorder and yields well-ordered SAMs. We discuss these findings in terms of differences in the surface mobility of 6MP species on these surfaces, the energetics of the adsorption sites, and the number of degrees of freedom of these substrates for a molecule with reduced surface mobility resulting from its two surface anchors. These results reveal the presence of subtle molecule-substrate interactions involving the heteroatom that drastically alter SAM properties and therefore strongly impact on our ability to control physical properties and to build devices at the nanoscale. Fil: Lobo Maza, Flavia Emilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Carro, Pilar. Universidad de La Laguna; España Fil: Vericat, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Kern, Klaus. Max Planck Institut für Festkörperforschung; Alemania Fil: Salvarezza, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Room temperature ferromagnetism was observed in rare earth dysprosium (Dy)-doped tris(8-hydroxyquinoline) aluminum (Alq3) organic small molecular films. The Dy-doped Alq3 films were prepared by co-evaporating pure Alq3 and Dy powders on Si substrates in a vacuum. The maximum room temperature coercive field and the saturation magnetization are about 70 Oe and 9.5 × 10−6 emu, respectively. The structures were studied by the atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and synchrotron radiation X-ray absorption fine structure (XAFS). The magnetic properties were investigated by the MicroMag Alternating Gradient Magnetometer (AGM), Quantum Design superconducting quantum interference device (SQUID) and first-principles calculations. The room temperature ferromagnetism is ascribed to the magnetic moments induced by the Dy atom and the large energy difference between ferromagnetic and antiferromagnetic coupling.

This research presents a general electrophoretic deposition (EPD) method, which offers selective preparation of various heteroatom-containing (i.e., H, Cl, F, N, and S) carboxylic acid molecular (CAM) films directly on silicon wafers, as long as the precursors are water-soluble carboxylic acids. Among them, the as-prepared fluoro-carboxylic acid (trifluoroacetic acid) molecular film with controllable thickness exhibits a longer wear life than self-assembled monolayers (SAMs), along with very low friction coefficient and a superior tolerance to humidity. It may be a promising candidate to replace SAMs as a more wear-resistant solid lubricant in micro/nano electromechanical systems (MEMS/NEMS).

To meet the lubrication demands of future MEMS/NEMS, thickness-controllable carbon films have been successfully prepared directly on silicon substrates by carbonizing electrophoresis-deposited trichloroacetic acid (TCA) molecular films. Compared with easily worn-out TCA molecular films, the transformed carbon films exhibit ultra-low friction coefficients and wear rates, along with strong adhesion to silicon substrates. These results prove that the idea of transforming organic molecular films into carbon thin films is a unique and promising approach to fabricate thickness-controllable and wear-resistant carbon-based solid lubricants for MEMS/NEMS.

Homoleptic monomolecular layers of optically-rich and redox-active Ru(II)-4′carboxylic-phenyl-2,2′:6′,2′′-terpyridyl (1) have been fabricated on SiOx-based substrates. The optical and redox properties of the films have been studied in detail. The molecular films showed high electrochemical and thermal stability. The combination of thermal and electrochemical stability of the surface-confined assemblies could be useful for potential applications in materials science.

Metal oxide thin films are increasingly utilized in small molecular organic photovoltaic devices to facilitate electron transport and injection. Despite this there is little understanding of the influence these layers have on the structure of adjacent organic semiconductor layers. Here we use both O- and Zn-terminated (0001) single crystal zinc oxide (ZnO) as a model system to investigate the effect of a metal oxide surface on the growth of a molecular semiconductor, vanadyl phthalocyanine (VOPc). The surface reconstructions of these model surfaces are determined and the properties of thin films of VOPc deposited atop are investigated. The nature of the bulk truncation of the surface is found to have pronounced effects on both the morphology and crystal structure of these molecular films. This work highlights the importance of considering the effects of the chemical composition and surface termination of metal oxide films on the structure of adjacent molecular semiconductor films.

The redox capacitance and its associated quantum component arising from the charging of molecular levels from coupled metallic states are resolvable and quantified experimentally by capacitance spectroscopy (CS). Herein we relate both this N-electron system capacitance directly to conceptual chemistry density functional theory (DFT) and the charging magnitude and associated quantum capacitive term (which resemble those introduced by Serge Luryi) to the Kohn-Sham frontier molecular orbital associated energies for isolated molecules and DFT calculated redox density of states (DOS) at metal-molecule junctions for a single molecule and molecular films confined at metallic interfaces. DFT computational analyses reveal the orbital energetic alignment between the iron redox site and those states in the metal specifically when metal-molecule junctions are formed. The impact of this on the resolved chemical softness and capacitance is also revealed. These analyses, additionally, are shown to numerically resolve redox capacitance in a manner that accurately reproduces experimental observations for molecular films. These observations both theoretically underpin CS and provide guidance on its optimised application in interfacial analyses involving molecular electrochemistry and derived sensory applications.

Sensitive, selective, low-cost, and simply designed detectors for THF among other vapour organic compounds (VOCs) are highly attractive. Self-assembled molecular films with remarkable selective vapoluminescent response to VOC THF were fabricated using drop-casting of calix[4]azacrown-based J-aggregates. The latter, stabilized via C–H⋯π and C–H⋯O hydrogen bond networks, assemble into nanoparticles that exhibit aggregation-induced emission (AIE) effect, which produces violet emission at room temperature in acetonitrile. The films are highly ordered and switch order at high temperature, leading to 2.5-fold luminescence enhancement and responsive behaviour.

Herein we demonstrate redox switchable emission from a sensitised, europium-ferrocene containing, molecular film assembled by a novel nitrene-based strategy. Electrochemical modulation of europium emission upon switching the ferrocene moiety's redox state is ascribed to the reversible generation of a quenching ferrocenium species.

The synthesis, electrochemical and spectroscopic properties of the new thiophene-substituted metal dithiolene complexes [Ni(b-3ted)2] (3) and [NBu4][Ni(b-3ted)2] ([NBu4][3]) are described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene] and compared with new studies of the known compounds [Ni(b-2ted)2] (2) and [NBu4][Ni(b-2ted)2] ([NBu4][2]). X-Ray structures were determined for the neutral complexes 2 and 3 and both showed planar nickel dithiolene units with thiophene groups twisted out of the molecular plane, precluding close molecular π-stacking. Electrochemical investigations revealed two redox processes corresponding to interconversion between neutral, monoanionic and dianionic species for 3, analogous to 2. Oxidation of 0.1 mM [3]− in CH3CN was shown to give a green molecular film of 3 which, in contrast to as-prepared crystals of 3, showed significant conductivity. Electrochemical polymerisation of 3 carried out at different concentrations resulted in films; electrochemical, SNIFTIRS and UV-Vis results were consistent with incorporation of the intact metal dithiolene complex in these films. In contrast, electrochemical polymerisation of 2 gave a film charateristic of a polymerised thiophene but with no evidence of incorporation of the intact metal dithiolene complex. Copolymerisation of 3 with thiophene gave a gold-coloured electropolymerised film of significant conductivity that, upon dissolution in CH2Cl2, showed the characteristic low energy absorption of the Ni-dithiolene complex, confirming its incorporation. This copolymerisation approach offers a versatile route to the synthesis of metal dithiolene–polythiophene hybrid films.

Novel photochromic hybrid organized molecular films composed of polyoxomolybdate (PMo12) and a series of gemini amphiphile (BisBC18Nn, n = 1, 2, 3) with different hydrophilic spacer length were fabricated by the Langmuir–Blodgett (LB) technique. When these gemini amphiphiles were spread on an aqueous PMo12 subphase, hybrid monolayers were formed in situ at the air/water interface through electrostatic interaction. These hybrid monolayers were subsequently transferred onto solid substrates and characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), atomic force microscopy (AFM) and cyclic voltammetry (CV). The hybrid multilayer films showed photochromic property, i.e., the color of BisBC18Nn/PMo12 hybrid films changed from pale yellow to cyan under UV irradiation and decoloration occurred when the films were heated in the air. Such processes could be repeated many times and the films exhibited excellent photochromic reversibility. A slight difference in the coloration of the hybrid films with different spacer lengths was observed.

New organic–inorganic hybrid molecular films, consisting of a Keggin-type polyoxometalate PW12 and a series of gemini amphiphiles with various lengths of the flexible spacers, have been fabricated using the Langmuir–Blodgett (LB) technique and the electrochemical properties of the hybrid films were investigated. When the positively charged gemini amphiphiles were spread on the aqueous subphase containing PW12, hybrid monolayers were formed in situ at the air/water interface through electrostatic interaction. The hybrid monolayers could be subsequently transferred onto solid substrates and the resulted multilayer films were characterized by UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements. Marked distinctions between the compression isotherms and different topographies of the transferred films were observed depending on the spacer length of the gemini amphiphiles. The electrochemical properties of the hybrid films were investigated by cyclic voltammetry (CV) and the second reduction peaks were found to shift gradually to negative with increasing spacer length. When the hybrid films were deposited onto glassy carbon electrode surfaces, the modified electrodes exhibited high electrocatalytic response to the reduction of NO2−. The effect of the spacer length of the gemini amphiphiles on the electrocatalytic efficiency of the hybrid films was also observed, and the greatest efficiency was achieved for the hybrid film composed of PW12 and the gemini with two methylenes as spacer.

Langmuir–Blodgett (LB) monolayers of squaraine dyes of general formula D–(C4O2)–D, where D is a heterocyclic donor, exhibit second-harmonic generation (SHG) with, for example, χzzz(2)=100–150 pm V–1 at 1.064 µm for 2,4-bis[(3,3-dimethylindolin-2-ylidene)methyl]squaraine. The behaviour is not an inherent property of the molecule and the second-order susceptibility is too high to arise from polarisation of the molecular film at the interface. Instead, the SHG is attributed to non-centrosymmetric aggregation with intermolecular charge transfer between the donor (heterocycle) and acceptor (C4O2) groups of adjacent molecules playing a significant role and contributing to the susceptibility. The nonlinear optical properties are discussed with reference to films of 1,4-bis(pyrrol-2-yl)squaraine derivatives which show either very weak or no SHG. The behaviour is dependent upon the type of aggregation and the extent of the donor–acceptor interaction.

Photopolymerized organized molecular films of polydiacetylene showed chirality although the monomeric amphiphilic diacetylene was achiral.

Optical spectroscopy is a powerful tool to study in depth manifold physical processes occurring in molecular solids, at interfaces between molecules and substrates, and at interfaces between different molecular species. Apart from probing the optical interactions themselves, also structural information can be deduced due to the sensitive dependence of the optical properties of molecular assemblies on the respective structure. In our contribution we review the method Differential Reflectance Spectroscopy (DRS), with special emphasis on the interpretation of the spectral data and the extraction of the material's properties, i.e., the complex dielectric function. We further elucidate which physical effects can be investigated. For this purpose we assess recent progress of DRS experiments and explain several selected results achieved with this technique.

Surface orientation of self-assembled molecular films of 2,9,6,23-tetraamino cobalt phthalocyanine on gold and silver is shown to determine the nature and the products of the electrocatalytic reduction of oxygen.

We report on the formation of organic-organic thin film heterostructures by co-sublimation, which exhibit either mixing of compounds on the molecular scale or pronounced phase separation into ordered domains on the micrometre scale. The mixed structures may be used as active layers in organic field effect transistors, while phase separation is useful in organic bulk hetero-junction solar cells. Pairs of five rod-like conjugated molecules were co-deposited onto silicon oxide substrates in vacuum. With the five materials: pentacene (PEN), alpha-quaterthiophene (4T), alpha-sexithiophene (6T), p-sexiphenyl (6P), and alkyl chain substituted α,ω-dihexylsexithiophene (DH6T), we investigated molecule pairs, which differ in the length of the molecular conjugated core (CC) and the overall molecular length. Material pairs with similarly sized CC, such as 4T/PEN and 6T/6P, showed the formation of ordered layered structures with intimated mixing on a molecular level. On the other hand, pronounced phase separation was observed for material pairs of dissimilar CC lengths, e.g. 4T/6T and PEN/DH6T. We propose that this can be generalized as design rule for the formation of either mixed or phase separated co-deposited molecular films.

The intrinsic flexibility of organic molecular films has been suggested to enable bendable electronics in comparison to their stiffer, inorganic counterparts. However, very little is known regarding the mechanical properties of these molecular glasses that are commonly utilized in organic electronics. To begin to address these issues, the elastic modulus of vapor deposited tris(8-hydroxyquinolinato)aluminium (Alq3) films, commonly used in organic light emitting devices (OLEDs), is determined as a function of thickness from 10 nm to 100 nm using a wrinkling-based metrology. These thicknesses correspond well with the range actually utilized in OLEDs. The direct deposition of Alq3 onto a polydimethylsiloxane (PDMS) elastomer results in anomalous results due to diffusion of Alq3 into the PDMS substrate. Conversely, a thin polystyrene (PS) film can be used as a diffusion barrier, enabling the elastic moduli to be accurately measured. Similar to most organic glasses, the Young's modulus of Alq3 is on the order of 1 GPa and is statistically invariant for thicknesses >20 nm. Interestingly, there is a significant increase in the Young's modulus for thinner films. The modulus of a 10 nm Alq3 film is found to be nearly twice that of a thicker film. Corresponding to this change in modulus is a loss of the optical adsorption peak associated with aggregation of Alq3, which suggests that the modulus change is related to the local packing of the molecule. This result illustrates that the thickness of active layers in OLEDs impacts not only the device performance but also their elastic properties, both of which are important for use in flexible devices.

The adsorption of aromatic thiols on Cu and the SAM film stability in acidic solutions have been studied by XPS, contact angle and electrochemical techniques. Three short molecules, benzenethiol (BT), 2-naphthalenethiol (2-NT) and 4-acetamidothiophenol (4-AA), were selected as representatives of aromatic thiols to highlight the effect of aromatic rings and hydrophilic terminal groups on the copper protection. All the three molecules form stable S-Cu bonds as a consequence of their adsorption process on polycrystalline copper. Although none of them provides a full copper passivation, the adsorbed films persist without major degradation on Cu electrodes even after 12 h immersion in 0.5 M sulfuric acid. Comparing the freshly prepared adsorbed films, the larger 2-NT molecule provides a better Cu passivation, but the shorter BT molecule favours a higher surface coverage. The terminal groups of 4-AA are responsible for a higher Cu surface wettability in water, compared to that with SAMs of the other molecules, and allow for an easier charge-transfer to the electrolyte and for a higher electrochemical capacitance. After long enough ageing, however, the 4-AA-based molecular films are able to self-organize and to provide a steadily improving copper passivation. Adlayers of the BT and 2-NT molecules, on the contrary, over a long time tend to protect less and less the Cu substrate, probably because of progressive electrolyte infiltration.

Gold nanoparticles (AuNPs) were adsorbed from an aqueous solution onto a poly(diphenylamine) (PDPA) monolayer at the air/liquid interface for preparing composite PDPA/AuNPs molecular films. The AuNPs were surface-modified by mercaptosuccinic acid (MSA) to enhance the electrostatic interaction between PDPA and the AuNPs. The behaviors of PDPA and mixed PDPA/AuNPs monolayers at the air/liquid interface were investigated using surface pressure-area (π-A) and surface potential-area (ΔV-A) isotherms, as well as the direct observation of Brewster Angle Microscopy (BAM). The surface structures of the corresponding Langmuir-Blodgett (LB) films were characterized by an Atomic Force Microscopy (AFM). The results show that the PDPA molecules form a condensed layer on pure water subphase, with small compressibility. The limiting molecular areas of PDPA estimated from both π-A and ΔV-A isotherms are very small, indicating that PDPA molecules were highly aggregated on pure water. This inference was confirmed by the observations of BAM and AFM. On the contrary, the mixed PDPA/AuNPs monolayer demonstrates a more expanded characteristic with a much larger limiting area in comparison with that of PDPA. Furthermore, the PDPA/AuNPs monolayer reveals a high uniform morphology without significant aggregative phases under the observation of BAM and AFM. It is inferred that the PDPA-AuNPs interaction fixes the PDPA chains on the surface of AuNPs, decreases the mobility and interaction of polymer chains, and therefore, inhibits the folding and aggregation of PDPA molecules. Therefore, highly extended PDPA molecules were obtained in the composite PDPA/AuNPs monolayer.

We demonstrate that small-molecule organic thin films of pentacene deposited from thermal and supersonic molecular beam sources can undergo significant reorganization under vacuum or in N2 atmosphere, beginning immediately after deposition of thin films onto SiO2 gate dielectric treated with hexamethyldisilazane (HMDS) and fluorinated octyltrichlorosilane (FOTS). Films deposited on bare SiO2 remain unchanged even after extended aging in vacuum. The changes observed on low-energy surfaces include the depletion of molecules in the interfacial monolayer resulting in the population of upper layers via upward interlayer transport of molecules, indicating a dewetting-like behavior. The morphology of pristine, as-deposited thin films was determined during growth by in situ real-time synchrotron X-ray reflectivity and was measured again, ex situ, by atomic force microscopy (AFM) following aging at room temperature in vacuum, in N2 atmosphere, and in ambient air. Important morphological changes are observed in ultra-thin films (coverage < 5 ML) kept in vacuum or in N2 atmosphere, but not in ambient air. AFM measurements conducted for a series of time intervals reveal that the rate of dewetting increases with decreasing surface energy of the gate dielectric. Films thicker than ∼5 ML remain stable under all conditions; this is attributed to the fact that the interfacial layer is buried completely for films thicker than ∼5 ML. This work highlights the propensity of small-molecule thin films to undergo significant molecular-scale reorganization at room temperature when kept in vacuum or in N2 atmosphere after the end of deposition; it should serve as a cautionary note to anyone investigating the behavior of organic electronic devices and its relationship with the initial growth of ultra-thin molecular films on low-energy surfaces.

Electrochemical properties of redox-active self-assembled molecular films of novel metallo-octacarboxyphthalocyanine (MOCPc, M = Fe, Co and Mn) complexes integrated with cysteamine (Cys) monolayer on gold electrodes via amide bonds were investigated. X-Ray photoelectron spectroscopy confirmed the appearance of the various elements in their expected chemical environment upon immobilization of these species. The heterogeneous electron transfer properties of the Au-Cys-MOCPc molecular films using an outer-sphere ([Fe(CN)(6)](4-)/[Fe(CN)(6)](3-)) redox probe were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The electron transfer rate constant (k(app)) depends markedly on the central metal of the metallophthalocyanine cores (k(app): CoMnFe). A strong pH dependence of the electron transport of the Au-Cys-MOCPc molecular films was found. The surface pK(a) values of the MOCPc complexes were essentially the same (ca. 7.5). The differences in the electron transports and ionization constants are discussed. The electrodes are sensitive to the electrooxidation of epinephrine in physiological pH conditions, peak potential (E(p)/V vs. Ag|AgCl, saturated KCl) decreasing as FeOCPc (0.20 V)MnOCPc (0.26 V)CoOCPc (0.34 V).

A synthetic strategy is described that provides access to oligopyridine-based ditopic ligands bridged by an alkyne spacer comprising one to four ethynyl groups. The spacer serves as both a rigid girder to maintain structural inetgrity and a conduit for electron flow. These ditopic ligands, bearing 2,2′-bipyridine, 1,10-phenanthroline or 2,2′:6′,2″-terpyridine coordination sites, are used to construct a dichotomous series of polynuclear metal complexes. Judicious selection of ligand and metal cation permits the assembly of novel molecular architectures incorporating a logical gradient of redox units along the molecular axis. Different molecular shapes become possible by changing the position at which the alkyne bridge is connected to the terminal ligand and varying the nature of the complexing cation. The elecrochemical and photochemical properties of many such molecular arrays are enumerated with a view to the future design of molecular electronic devices. The alkyne bridge actively promotes long-range electronic coupling between remote cationic units, especially under illumination with visible light. Intramolecular triplet energy transfer, photon migration and light-induced electron transfer occur by way of extremely rapid superexchange involving LUMO and HOMO states localized on the bridge. It is also shown that facile electron delocalization over an extended π* orbital takes place in the triplet excited states of symmetrical binuclear complexes. This process extends the triplet lifetime and thereby facilitates secondary reactions that are otherwise unattainable. The level of electronic communication along the molecular wire can be controlled by insertion of suitable insulating groups into the bridge, these groups also providing further means by which to manipulate the stereochemistry. In certain cases, the alkyne bridge undergoes reductive electropolymerization to generate molecular films having metallo centres dispersed along a conjugated backbone.

The lateral viscoelastic properties of mica surfaces bearing deposited films of phospholipids have been determined. These experiments have been conducted using a modified form of the mica surface forces apparatus, SFA. In this experiment a monolayer of a phospholipid is deposited onto two mica surfaces from a Langmuir–Blodgett deposition trough. The two surfaces are then placed in contact in the SFA. A small displacement, typically 100 nm, is then applied in a sinusoidal manner to one of the surfaces through a piezoelectric bimorph. A second bimorph acts a receiver. From the amplitudes and phase angle of the input and output signals, the viscoelastic properties of the molecular films of the phospholipids may be determined. The results show that all the films were more elastic than viscous, a consequence of the high surface pressures at which the films were transferred from the Langmuir trough, and that the elastic modulus decreased with increasing load applied to the two surfaces.

The problem of optical absorption due to oriented molecular films adsorbed within porous media has been treated theoretically in the approximation that the adsorbent behaves as a collection of spherical particles or cavities of small size compared with the wavelength of light. Expressions for the contribution to the spectrum arising from optical modes involving charge displacement parallel to the local substrate surface, relative to those involving normal displacements, are derived from which a number of conclusions are reached. Thus for example it is shown that in general the relative intensities of different absorption bands are dependent upon the detailed geometry of the porous adsorbent. The equations presented offer the first opportunity for quantitative interpretation of infra-red absorption spectra for porous adsorbent-adsorbate systems.