Chemosensation in anxiety: the trigeminal system matters.

The presence of a perceptual bias due to anxiety is well demonstrated in cognitive and sensory task for the visual and auditory modality. Event-related potentials, by their specific measurement of neural processes, have strongly contributed to this evidence. There is still no consensus as to whether such a bias exists in the chemical senses; chemosensory event-related potentials (CSERPs) are an excellent tool to clarify the heterogeneous results, especially since the Late Positive Component (LPC) may be an indicator of emotional involvement after chemosensory stimulation. This research examined the association between state and trait anxiety and the amplitude and latency of pure olfactory and mixed olfactory-trigeminal LPC. In this study, 20 healthy participants (11 women) with a mean age of 24.6 years (SD = 2.6) completed a validated questionnaire to measure anxiety (STAI), and CSERP was recorded during 40 pure olfactory stimulations (phenyl ethanol) and 40 mixed olfactory-trigeminal stimulations (eucalyptol). LPC latency and amplitude were measured at Cz (electrode located at midline central) for each participant. We observed a significant negative correlation between LPC latencies and the state anxiety scores for the mixed olfactory-trigeminal condition (r(18) = -0.513; P = 0.021), but not for the pure olfactory condition. We did not observe any effect on LPC amplitudes. This study suggests that a higher level of state anxiety is related to a more rapid perceptual electrophysiological response for mixed olfactory-trigeminal stimuli but not for pure odors.

Verbal Episodic Memory Alterations and Hippocampal Atrophy in Acute Mild Traumatic Brain Injury.

Episodic memory deficit is a symptom frequently observed after a mild traumatic brain injury (mTBI). However, few studies have investigated the impact of a single and acute mTBI on episodic memory and structural cerebral changes. To do so, we conducted two experiments. In the first, we evaluated verbal episodic memory by using a word recall test, in 52 patients with mTBI (mean age 33.1 [12.2] years) 2-4 weeks after a first mTBI, compared with 54 healthy controls (31.3 [9.2] years) and followed both groups up for 6 months. In the second, we measured hippocampal volume in a subset of 40 participants (20 patients with mTBI, 20 controls) from Experiment 1 using magnetic resonance imaging (MRI; T1-weighted images) and correlated memory performance scores to hippocampal volume. Experiment 1 showed significantly reduced verbal episodic memory within the first month after an mTBI and a tendency for a reduction 6 months later, more pronounced for men. In Experiment 2, patients with mTBI exhibited a generally reduced hippocampal volume; however, we did not observe any linear correlation between hippocampal volume and memory scores. These results suggest that one single mTBI is associated with both episodic memory alteration and reduced volume of the hippocampus in the acute phase. Future studies are needed to elucidate the link between both measures.

Revisiting the Optimal Nano-Morphology: Towards Amorphous Organic Photovoltaics.

Organic photovoltaic cells commonly use an active layer with a polycrystalline bulk heterojunction. However, for simplifying the fabrication process, it may be worthwhile to use an amorphous active layer to lessen the burden on processing to achieve optimal performance. While polymers can adopt amorphous phases, molecular glasses, small molecules that can readily form glassy phases and do not crystallize over time, offer an appealing alternative, being monodisperse species. Our group has developed a series of reactive molecular glasses that can be covalently bonded to chromophores to form glass-forming adducts, and this strategy has been used to synthesize glass-forming donor and acceptor materials. Herein, the results of devices incorporating these materials in either partially or fully amorphous active layers are summarized. Additionally, these molecular glasses can be used as ternary components in crystalline systems to enhance efficiency without perturbing the morphology.

Simple Unbiased Hot-Electron Polarization-Sensitive Near-Infrared Photodetector.

Plasmonic nanostructures can generate energetic "hot" electrons from light in a broad band fashion depending on their shape, size, and arrangement. Such structures have a promising use in photodetectors, allowing high speed, broad band, and multicolor photodetection. Because they function without a band gap absorption, photon detection at any energy would be possible through engineering of the plasmonic nanostructure. Herein, a compact hot-electron-based photodetector that combines polarization sensitivity and circularly polarized light detection in the near-infrared region was fabricated using an indium tin oxide (ITO)-Au hybrid layer. Furthermore, the sensitivity of the device was significantly increased by adding a poled Azo molecular glass film in a capacitor configuration. The resulting device is capable of detecting light below the ITO band gap at ambient temperature without any bias voltage. This photodetector, which is amenable to large-area fabrication, can be integrated with other nanophotonic and nanoplasmonic structures for operation at telecom wavelengths.

Transfer of chirality from light to a Disperse Red 1 molecular glass surface.

Chiral structures and materials interact with light in well-documented ways, but light can also interact with achiral materials to generate chirality by inscribing its asymmetric configuration on photoresponsive materials, such as azobenzene derivatives. While it is thus possible to generate both two-dimensional (2D) and three-dimensional (3D) chirality, 2D chirality is especially attractive because of its non-reciprocity. Herein, 2D chirality is induced on the surface of a glass-forming Disperse Red 1 derivative by irradiation with a single laser beam, yielding crossed spontaneous surface relief gratings with different pitches. Azimuth rotations up to 10° have been observed, and the absence of 3D chirality has been confirmed. This method thus allows generating non-reciprocal planar chiral objects by a simple, single irradiation process on a thin film of a material that can easily be processed over large areas or onto small objects.

Influence of Hydrogen Bonding on the Surface Diffusion of Molecular Glasses: Comparison of Three Triazines.

Surface grating decay measurements have been performed on three closely related molecular glasses to study the effect of intermolecular hydrogen bonds on surface diffusion. The three molecules are derivatives of bis(3,5-dimethyl-phenylamino)-1,3,5-triazine and differ only in the functional group R at the 2-position, with R being C2H5, OCH3, and NHCH3, and referred to as "Et", "OMe", and "NHMe", respectively. Of the three molecules, NHMe forms more extensive intermolecular hydrogen bonds than Et and OMe and was found to have slower surface diffusion. For Et and OMe, surface diffusion is so fast that it replaces viscous flow as the mechanism of surface grating decay as temperature is lowered. In contrast, no such transition was observed for NHMe under the same conditions, indicating significantly slower surface diffusion. This result is consistent with the previous finding that extensive intermolecular hydrogen bonds slow down surface diffusion in molecular glasses and is attributed to the persistence of hydrogen bonds even in the surface environment. This result is also consistent with the lower stability of the vapor-deposited glass of NHMe relative to those of Et and OMe and supports the view that surface mobility controls the stability of vapor-deposited glasses.

Influence of Hydrogen Bonding on the Kinetic Stability of Vapor-Deposited Glasses of Triazine Derivatives.

It has recently been established that physical vapor deposition (PVD) can produce organic glasses with enhanced kinetic stability, high density, and anisotropic packing, with the substrate temperature during deposition (Tsubstrate) as the key control parameter. The influence of hydrogen bonding on the formation of PVD glasses has not been fully explored. Herein, we use a high-throughput preparation method to vapor-deposit three triazine derivatives over a wide range of Tsubstrate, from 0.69 to 1.08Tg, where Tg is the glass transition temperature. These model systems are structural analogues containing a functional group with different H-bonding capability at the 2-position of a triazine ring: (1) 2-methylamino-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (NHMe) (H-bond donor), (2) 2-methoxy-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (OMe) (H-bond acceptor), and (3) 2-ethyl-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (Et) (none). Using spectroscopic ellipsometry, we find that the Et and OMe compounds form PVD glasses with relatively high kinetic stability, with the transformation time (scaled by the α-relaxation time) on the order of 103, comparable to other highly stable glasses formed by PVD. In contrast, PVD glasses of NHMe are only slightly more stable than the corresponding liquid-cooled glass. Using IR spectroscopy, we find that both the supercooled liquid and the PVD glasses of the NHMe derivative show a higher average number of bonded NH per molecule than that in the other two compounds. These results suggest that H-bonds hinder the formation of stable glasses, perhaps by limiting the surface mobility. Interestingly, despite this difference in kinetic stability, all three compounds show properties typically observed in highly stable glasses prepared by PVD, including a higher density and anisotropic molecular packing (as characterized by IR and wide-angle X-ray scattering).

Photoactive/Passive Molecular Glass Blends: An Efficient Strategy to Optimize Azomaterials for Surface Relief Grating Inscription.

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Disperse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol % of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE, and initial inscription rate reach a maximum when Tg is 25-40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol % azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE 6-fold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo-orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo-orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

Photoinduction of spontaneous surface relief gratings on Azo DR1 glass.

Surface relief gratings were spontaneously photoinduced from a collimated Nd:YAG laser beam at 532 nm on thin films of a disperse red 1 functionalized glass-forming compound. Pattern formation was studied by measuring the diffraction intensity of a He-Ne laser probe beam at 633 nm and by atomic force microscopy (AFM). The dependence of pattern formation on both irradiation time and intensity was studied. The gratings could be erased both optically and thermally. The orientation of the gratings is influenced by the polarization of the writing beam, and it is accompanied by strong diffraction of the incident light into the sample plane, thereby providing a way to couple and trap the light into the substrate. Interestingly, photobleaching upon prolonged irradiation yields transparent gratings, and the process is partially reversible upon thermal erasure.

Electric-Field-Induced Nanoscale Surface Patterning in Mexylaminotriazine-Functionalized Molecular Glass Derivatives.

Nanoscale surface patterns were observed in thin films of mexylaminotriazine-functionalized glasses containing polar groups upon the application of an electric field at temperatures over their glass transition temperatures (Tg). This phenomenon occurred due to the surface deformation process initiated by external electric field instabilities on the films. The minimal surface deformation temperature (Tdewet) relative to Tg was found to increase as a function of the polarity of the substituents and the surface pattern roughness was observed to increase linearly with temperature for a fixed electric field and exposure time. Reversal of the electrical field polarity and the use of both hydrophilic and hydrophobic substrates did not significantly change the surface deformation behavior of the films, which is due to the deposition of charges at the free interface. The application of a mask between the electric field electrodes allowed to selectively pattern areas that are exposed. Furthermore, it was observed that this surface deformation behavior was reversible, since heating the films to a temperature above Tg in the absence of an electric field caused the erasure of all surface patterns.

Unraveling the interplay between hydrogen bonding and rotational energy barrier to fine-tune the properties of triazine molecular glasses.

Mexylaminotriazine derivatives form molecular glasses with outstanding glass-forming ability (GFA), high resistance to crystallization (glass kinetic stability, GS), and a glass transition temperature (Tg) above room temperature that can be conveniently modulated by selection of the headgroup and ancillary groups. A common feature of all these compounds is their secondary amino linkers, suggesting that they play a critical role in their GFA and GS for reasons that remain unclear because they can simultaneously form hydrogen (H) bonds and lead to a high interconversion energy barrier between different rotamers. To investigate independently and better control the influence of H bonding capability and rotational energy barrier on Tg, GFA and GS, a library of twelve analogous molecules was synthesized with different combinations of NH, NMe and O linkers. Differential scanning calorimetry (DSC) revealed that these compounds form, with a single exception, kinetically stable glasses with Tg values spanning a very broad range from -25 to 94 °C. While variable temperature infrared spectroscopy combined to chemometrics reveals that, on average, around 60% of the NH groups are still H-bonded as high as 40 °C above Tg, critical cooling rates obtained by DSC clearly show that molecules without H-bond donating linkers also present an outstanding GFA, meaning that H bonding plays a dominant role in controlling Tg but is not required to prevent crystallization. It is a high interconversion energy barrier, provoking a distribution of rotamers, that most efficiently promotes both GFA and resistance to crystallization. These new insights pave the way to more efficient glass engineering by extending the possible range of accessible Tg, allowing in particular the preparation of homologous glass-formers with high GS at ambient temperature in either the viscous or vitreous state.

Submolecular Plasticization Induced by Photons in Azobenzene Materials.

We demonstrate experimentally for the first time that the illumination of azobenzene derivatives leads to changes in molecular environment similar to those observed on heating but that are highly heterogeneous at the submolecular scale. This localized photoplasticization, which can be associated with a free volume gradient, helps to understand the puzzling phenomenon of photoinduced macroscopic material flow and photoexpansion upon illumination far below the glass transition temperature (T(g)). The findings stem from the correlation of infrared (IR) spectral band shifts measured upon illumination with those measured at controlled temperatures for two amorphous DR1-functionalized azo derivatives, a polymer, pDR1A, and a molecular glass, gDR1. This new approach reveals that IR spectroscopy can be used as an efficient label-free molecular-scale thermometer that allows the assignment of an effective temperature (T(eff)) to each moiety in these compounds when irradiated. While no band shift is observed upon illumination for the vibrational modes assigned to backbone moieties of pDR1A and gDR1 and a small band shift is found for the spacer moiety, dramatic band shifts are recorded for the azo moiety, corresponding to an increase in T(eff) of up to nearly 200 °C and a molecular environment that is equivalent to thermal heating well above the bulk T(g) of the material. An irradiated azo-containing material thus combines characteristic properties of amorphous materials both below and above its bulk T(g). The direct measurement of T(eff) is a powerful probe of the local environment at the submolecular scale, paving the way toward better rationalization of photoexpansion and the athermal malleability of azo-containing materials upon illumination below their T(g).

Design and fabrication of constant-pitch circular surface-relief diffraction gratings on disperse red 1 glass.

Circular surface-relief diffraction gratings with a constant pitch were photo-inscribed on thin films of a disperse red 1 functionalized glass-forming compound using a novel holographic technique. Various light-interfering metallic fixtures, which consisted of annular rings with a sloped and polished inner surface, were designed and fabricated. Each of them allowed the inscription of stable and high-quality circular diffraction gratings with pitches ranging from approximately 600-1400 nm and depths up to 250 nm. This was accomplished by exposure to a collimated laser beam with an irradiance of 604 mW/cm2 for 350 s. The resulting gratings had a diameter of 11.4 mm and had the advantage of being produced in a simple single-step procedure with no postprocessing or specialized equipment. The pitch and diameter of these circular gratings were dependent on the fixture geometry, while the depth was related to the exposure time.

Synthesis, structure and magnetism of homodinuclear complexes of Co, Ni and Cu supported by a novel bitriazine scaffold.

Btzn (1), an amine-functionalized bi(1,3,5-triazine) 4,4'-(NH(2))(2)-6,6'-(NHC(6)H(5))(2)-2,2'-(1,3,5-C(3)N(3))(2), is reported, and its coordination with Co, Ni and Cu is explored. Reactions of metal salts (2 equiv) with Btzn (1 equiv) result in dimeric species [(Btzn)Co(2)(NCS)(4)(EtOH)(2)(DMF)(2)], (2), [(Btzn)Ni(2)(η(1)-ONO(2))(2)(MeOH)(4)(DMF)(2)]·2[NO(3)], (3), [(Btzn)Cu(2)Cl(4)(DMF)(2)], (4), and [(Btzn)Cu(2)(η(2)-O(2)NO)(2)(OH(2))(2)(DMF)(2)]·2[NO(3)], (5). These complexes are the first examples of the coordination of transition metals with bi(1,3,5-triazine) ligands. Their structures display a bridging bis-bidentate coordination mode for Btzn. Variable-temperature magnetic susceptibility of the complexes reveals antiferromagnetic exchange between the spin carriers, with calculated exchange coupling values (J) of -4.7 cm(-1) for 3, -18.2 cm(-1) for 4, and -5.5 cm(-1) for 5. An in-depth evaluation of the metal geometry highlights the inefficient overlap of the magnetic d-orbitals through the bridging ligand, most likely leading to reduced delocalization and coupling.

Syntheses and structures of isomeric diaminotriazinyl-substituted 2,2'-bipyridines and 1,10-phenanthrolines.

Isomeric 2,2'-bipyridines 4a-6a and 1,10-phenanthrolines 7a-9a with two diaminotriazinyl (DAT) substituents were synthesized to explore their dual ability to direct association by the chelation of metals and the characteristic hydrogen bonding of DAT groups. Crystals of compounds 4a-6a and 7a-9a were grown under diverse conditions, and their structures were solved by X-ray crystallography. Analysis revealed multiple shared features analogous to those observed in the structures of simpler DAT-substituted pyridines 1-3. For example, the bipyridines and phenanthrolines favor flattened conformations except in the cases of compounds 8a and 9a, where the patterns of substitution prevent the DAT groups from lying in the plane of the phenanthroline core. As expected, the DAT groups form approximately coplanar hydrogen bonds according to standard motifs I-III, which play a key role in directing molecular organization. However, the structures of simple pyridines 1-3, which favor efficiently packed chains and sheets, differ predictably from those of bipyridines 4a-6a and phenanthrolines 7a-9a in two ways: (1) The larger number of DAT groups in compounds 4a-9a typically leads to complex three-dimensional networks held together by a larger number of hydrogen bonds per molecule, and (2) the need to respect multiple directional interactions prevents compounds 4a-9a from forming closely packed structures, and significant quantities of guests are included. Together, these observations confirm the effectiveness of incorporating special groups such as DAT within more complex molecular structures to control association according to reliable patterns. Bipyridines 4a-6a and phenanthrolines 7a-9a promise to be particularly rich sources of new supramolecular chemistry because they have well-defined molecular topologies and a dual ability to direct association by chelating metals and by engaging in multiple hydrogen bonds according to reliable patterns.

Linker-directed vertex desymmetrization for the production of coordination polymers with high porosity.

Five non-interpenetrated microporous coordination polymers (MCPs) are derived by vertex desymmetrization using linkers with symmetry inequivalent coordinating groups, and these MCPs include properties such as rare metal clusters, new network topologies, and supramolecular isomerism. Gas sorption in polymorphic frameworks, UMCM-152 and UMCM-153 (based upon a copper-coordinated tetracarboxylated triphenylbenzene linker), reveals nearly identical properties with BET surface areas in the range of 3300-3500 m(2)/g and excess hydrogen uptake of 5.7 and 5.8 wt % at 77 K. In contrast, adsorption of organosulfur compounds dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) shows remarkably different capacities, providing direct evidence that liquid-phase adsorption is not solely dependent on surface area or linker/metal cluster identity. Structural features present in MCPs derived from these reduced symmetry linkers include the presence of more than one type of Cu-paddlewheel in a structure derived from a terphenyl tricarboxylate (UMCM-151) and a three-bladed zinc paddlewheel metal cluster in an MCP derived from a pentacarboxylated triphenylbenzene linker (UMCM-154).

A glass forming module for organic molecules: making tetraphenylporphyrin lose its crystallinity.

Formation of stable glassy phases can be induced through rational design in compounds which otherwise readily crystallize, such as tetraphenylporphyrin, by simple functionalization with moieties known to promote glass formation such as mexylaminotriazine units.

Tg and rheological properties of triazine-based molecular glasses: incriminating evidence against hydrogen bonds.

Bis(mexylamino)triazines have been identified as a family of compounds showing an exceptional propensity to form glassy phases as opposed to crystals. The particularities of this family of compounds are their ability to self-assemble through hydrogen bonding in well-defined patterns to form supramolecular aggregates which pack poorly and the wide range of glass transition temperatures (T(g)) that can be attained through minor structural modifications. Representative bis(mexylamino)triazines were studied by rheology to establish correlations between their rheological properties and their molecular structure, and all compounds were found to behave in a similar fashion except for the temperature at which glass transition takes place. FTIR and NMR spectroscopy experiments were performed on the molecular glasses studied herein; comparisons between the viscosity, T(g), hydrogen bonding, and association constant (K(a)) in CDCl3 solution have revealed a relationship between the rheological properties, the T(g) of the molecular glasses, and the extent and strength of hydrogen bonding present in the material.

Porous crystal derived from a tricarboxylate linker with two distinct binding motifs.

The use of a reduced symmetry organic linker for the preparation of porous coordination polymers is demonstrated. The solvothermal reaction of the unsymmetrically substituted biaryl compound biphenyl-3,4',5-tricarboxylic acid with Cu(II) ions produces a [3,4,6]-connected coordination polymer exhibiting very high porosity and surface area (SLangmuir = 3100 m2/g). A striking feature of the structure is its incorporation, in a single material, of both the ubiquitous dinuclear Cu(II) paddlewheel motif and the rarely observed trinuclear Cu(II) cluster. Saturation H2 uptake, measured at 77 K, shows an excess gravimetric uptake of 5.7 wt % at 45 bar with a steep rise at low pressures.

The dark side of crystal engineering: creating glasses from small symmetric molecules that form multiple hydrogen bonds.

Glasses made from compounds of low molecular weight are useful materials with many attractive features, including well-defined compositions. At present, there are no reliable ways to identify molecules that will form long-lived glasses, and efforts to design them have tended to rely on crude principles, such as avoiding small, symmetric, and relatively inflexible molecules that engage in strong intermolecular association. We have found that it is possible to make glasses from such molecules by turning to the dark side of crystal engineering and by making small but carefully selected structural modifications specifically designed to thwart established patterns of crystallization.