Influence of regionality and maturation time on the chemical fingerprint of whisky.

Understanding the chemical composition of whisky and the impact of each step in the manufacturing process provides a basis for responding to the challenges of producing high quality spirits. In this study, the objective was to discriminate whiskies according to their geographical origin and authenticate the maturation time in cask based on the non-volatile profiles. The combination of FT-ICR-MS and chemometrics allowed the distinction of whiskies from four geographical origins in Scotland (Highlands, Lowlands, Speyside and Islay). Statistical modeling was also used to discriminate whiskies according to the maturation time in cask and reveal chemical markers associated with the ageing regardless of the origin or the production process. Interestingly, the flow of transfer of compounds from wood barrels to distillates is not constant and homogeneous over the maturation time. The largest transfer of compounds from the barrel to the whisky was observed around twelve years of maturation.

Usage of FT-ICR-MS Metabolomics for Characterizing the Chemical Signatures of Barrel-Aged Whisky.

Whisky can be described as a complex matrix integrating the chemical history from the fermented cereals, the wooden barrels, the specific distillery processes, aging, and environmental factors. In this study, using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), we analyzed 150 whisky samples from 49 different distilleries, 7 countries, and ranging from 1 day new make spirit to 43 years of maturation with different types of barrel. Chemometrics revealed the unexpected impact of the wood history on the distillate's composition during barrel aging, regardless of the whisky origin. Flavonols, oligolignols, and fatty acids are examples of important chemical signatures for Bourbon casks, whereas a high number of polyphenol glycosides, including for instance quercetin-glucuronide or myricetin-glucoside as potential candidates, and carbohydrates would discriminate Sherry casks. However, the comparison of barrel aged rums and whiskies revealed specific signatures, highlighting the importance of the initial composition of the distillate and the distillery processes.

Opposite Surface and Bulk Solvatochromic Effects in a Molecular Spin-Crossover Compound Revealed by Ambient Pressure X-ray Absorption Spectroscopy.

We investigate the solvatochromic effect of a Fe-based spin-crossover (SCO) compound via ambient pressure soft X-ray absorption spectroscopy (AP-XAS) and atomic force microscopy (AFM). AP-XAS provides the direct evidence of the spin configuration for the Fe(II) 3d states of the SCO material upon in situ exposure to specific gas or vapor mixtures; concurrent changes in nanoscale topography and mechanical characteristics are revealed via AFM imaging and AFM-based force spectroscopy, respectively. We find that exposing the SCO material to gaseous helium promotes an effective decrease of the transition temperature of its surface layers, while the exposure to methanol vapor causes opposite surfacial and bulk solvatochromic effects. Surfacial solvatochromism is accompanied by a dramatic reduction of the surface layers stiffness. We propose a rationalization of the observed effects based on interfacial dehydration and solvation phenomena.

Correlation of the structural information obtained for europium-chelate ensembles from gas-phase photoluminescence and ion-mobility spectroscopy with density-functional computations and ligand-field theory.

We report a combined investigation of europium(iii)9-oxo-phenalen-1-one (PLN) coordination complexes, [Eu(PLN)4AE]+ with AE = Mg, Ca, and Sr, using gas-phase photoluminescence, trapped ion-mobility spectrometry and density-functional computations. In order to sort out the structural impact of the alkali earth dications on the photoluminescence spectra, the experimental data are compared to the predicted ligand-field splittings as well as to the collision cross-sections for different isomers of [Eu(PLN)4AE]+. The best fitting interpretation is that one isomer family predominantly contributes to the recorded luminescence. The present work demonstrates the complexity of the coordination patterns of multicenter lanthanoid chelates involved in dynamical equilibria and the pertinence of using isolation techniques to elucidate their photophysical properties.

A luminescent Pt2Fe spin crossover complex.

A heterotrinuclear [Pt2Fe] spin crossover (SCO) complex was developed and synthesized employing a ditopic bridging bpp-alkynyl ligand L and alkynyl coordinated PtII terpy units: [FeII(L-PtII)2]2(BF4)2 (1). We identified two different types of crystals of 1 which differ in their molecular packing and the number of co-crystallized solvent molecules: 1H (1·3.5CH2Cl2 in P1[combining macron]) and 1L (1·10CH2Cl2 in C2/c); while 1L shows a reversible SCO with a transition temperature of 268 K, the analogous compound 1H does not show any SCO and remains blocked in the HS state. The temperature-dependent magnetic properties of 1H and 1L were complementarily studied by Mössbauer spectroscopy. It has been shown that 1L performs thermal spin crossover and that 1L can be excited to a LIESST state. The vibrational properties of 1 were investigated by experimental nuclear resonance vibrational spectroscopy. The experimentally determined partial density of vibrational states (pDOS) was compared to a DFT-based simulation of the pDOS. The vibrational modes of the different components were assigned and visualized. In addition, the photophysical properties of 1 and L-Pt were investigated in the solid state and in solution. The ultrafast transient absorption spectroscopy of 1 in solution was carried out to study the PL quenching channel via energy transfer from photoexcited PtII terpy units to the FeII-moiety.

Controlled manipulation of the Co-Alq3 interface by rational design of Alq3 derivatives.

Recently, research has revealed that molecules can be used to steer the local spin properties of ferromagnetic surfaces. One possibility to manipulate ferromagnetic-metal-molecule interfaces in a controlled way is to synthesize specific, non-magnetic molecules to obtain a desired interaction with the ferromagnetic substrate. Here, we have synthesized derivatives of the well-known semiconductor Alq3 (with q = 8-hydroxyquinolinate), in which the 8-hydroxyquinolinate ligands are partially or completely replaced by similar ligands bearing O- or N-donor sets. The goal of this study was to investigate how the presence of (i) different donor atom sets and (ii) aromaticity in different conjugated π-systems influences the spin properties of the metal-molecule interface formed with a Co(100) surface. The spin-dependent metal-molecule-interface properties have been measured by spin-resolved photoemission spectroscopy, backed up by DFT calculations. Overall, our results show that, in the case of the Co-molecule interface, chemical synthesis of organic ligands leads to specific electronic properties of the interface, such as exciton formation or highly spin-polarized interface states. We find that these properties are even additive, i.e. they can be engineered into one single molecular system that incorporates all the relevant ligands.

Divergent Coordination Chemistry: Parallel Synthesis of [2×2] Iron(II) Grid-Complex Tauto-Conformers.

The coordination of iron(II) ions by a homoditopic ligand L with two tridentate chelates leads to the tautomerism-driven emergence of complexity, with isomeric tetramers and trimers as the coordination products. The structures of the two dominant [Fe(II) 4 L4 ](8+) complexes were determined by X-ray diffraction, and the distinctness of the products was confirmed by ion-mobility mass spectrometry. Moreover, these two isomers display contrasting magnetic properties (Fe(II) spin crossover vs. a blocked Fe(II) high-spin state). These results demonstrate how the coordination of a metal ion to a ligand that can undergo tautomerization can increase, at a higher hierarchical level, complexity, here expressed by the formation of isomeric molecular assemblies with distinct physical properties. Such results are of importance for improving our understanding of the emergence of complexity in chemistry and biology.

Surface induces different crystal structures in a room temperature switchable spin crossover compound.

We investigated the influence of surfaces in the formation of different crystal structures of a spin crossover compound, namely [Fe(L)2] (LH: (2-(pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine), which is a neutral compound thermally switchable around room temperature. We observed that the surface induces the formation of two different crystal structures, which exhibit opposite spin transitions, i.e. on heating them up to the transition temperature, one polymorph switches from high spin to low spin and the second polymorph switches irreversibly from low spin to high spin. We attributed this inversion to the presence of water molecules H-bonded to the complex tetrazolyl moieties in the crystals. Thin deposits were investigated by means of polarized optical microscopy, atomic force microscopy, X-ray diffraction, X-ray absorption spectroscopy and micro Raman spectroscopy; moreover the analysis of the Raman spectra and the interpretation of spin inversion were supported by DFT calculations.

Photoluminescence Spectroscopy of Mass-Selected Electrosprayed Ions Embedded in Cryogenic Rare-Gas Matrixes.

An apparatus is presented which combines nanoelectrospray ionization for isolation of large molecular ions from solution, mass-to-charge ratio selection in gas-phase, low-energy-ion-beam deposition into a (co-condensed) inert gas matrix and UV laser-induced visible-region photoluminescence (PL) of the matrix isolated ions. Performance is tested by depositing three different types of lanthanoid diketonate cations including also a dissociation product species not directly accessible by chemical synthesis. For these strongly photoluminescent ions, accumulation of some femto- to picomoles in a neon matrix (over a time scale of tens of minutes to several hours) is sufficient to obtain well-resolved dispersed emission spectra. We have ruled out contributions to these spectra due to charge neutralization or fragmentation during deposition by also acquiring photoluminescence spectra of the same ionic species in the gas phase.

Highly luminescent charge-neutral europium(iii) and terbium(iii) complexes with tridentate nitrogen ligands.

We report on the synthesis of tridentate-nitrogen pyrazole-pyridine-tetrazole (L(1)H) and pyrazole-pyridine-triazole (L(2)H) ligands and their complexation with lanthanides (Ln = Gd(iii), Eu(iii) and Tb(iii)) resulting in stable, charge-neutral complexes Ln(L(1))3 and Ln(L(2))3, respectively. X-ray crystallographic analysis of the complexes with L(1) ligands revealed tricapped trigonal coordination geometry around the lanthanide ions. All complexes show bright photoluminescence (PL) in the solid state, indicating efficient sensitization of the lanthanide emission via the triplet states of the ligands. In particular, the terbium complexes show high PL quantum yields of 65 and 59% for L(1) and L(2), respectively. Lower PL efficiencies of the europium complexes (7.5 and 9%, respectively) are attributed to large energy gaps between the triplet states of the ligands and accepting levels of Eu(iii). The triplet state energy can be reduced by introducing an electron withdrawing (EW) group at the 4 position of the pyridine ring. Such substitution of L(1)H with a carboxylic ester (COOMe) EW group leads to a europium complex with increased PL quantum yield of 31%. A comparatively efficient PL of the complexes dissolved in ethanol indicates that the lanthanide ions are shielded against nonradiative deactivation via solvent molecules.

Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation.

We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be -5.93 and -3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10(-6) and 2.1 × 10(-6) cm(2)·V(-1)·s(-1) was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10(-6) cm(2)·V(-1)·s(-1) and a hole mobility of 1.4 × 10(-4) cm(2)·V(-1)·s(-1). The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement.

Palladium versus platinum: the metal in the catalytic center of a molecular photocatalyst determines the mechanism of the hydrogen production with visible light.

To develop highly efficient molecular photocatalysts for visible light-driven hydrogen production, a thorough understanding of the photophysical and chemical processes in the photocatalyst is of vital importance. In this context, in situ X-ray absorption spectroscopic (XAS) investigations show that the nature of the catalytically active metal center in a (N^N)MCl2 (M=Pd or Pt) coordination sphere has a significant impact on the mechanism of the hydrogen formation. Pd as the catalytic center showed a substantially altered chemical environment and a formation of metal colloids during catalysis, whereas no changes of the coordination sphere were observed for Pt as catalytic center. The high stability of the Pt center was confirmed by chloride addition and mercury poisoning experiments. Thus, for Pt a fundamentally different catalytic mechanism without the involvement of colloids is confirmed.

Characterization of Nonanuclear Europium and Gadolinium Complexes by Gas-Phase Luminescence Spectroscopy.

Gas-phase measurements using mass-spectrometric techniques allow determination of the luminescence properties of selected molecular systems with knowledge of their exact composition. Furthermore, isolated luminophores are unaffected by matrix effects like solvent interactions or crystal packing. As a result, the system complexity is reduced relative to the condensed phase and a direct comparison with theory is facilitated. Herein, we report the intrinsic luminescence properties of nonanuclear europium(III) and gadolinium(III) 9-hydroxyphenalen-1-one (HPLN)-hydroxo complexes. Luminescence spectra of [Eu9(PLN)16(OH)10](+) ions reveal an europium-centered emission dominated by a 4-fold split Eu(III) hypersensitive transition. The corresponding Gd(III) complex, [Gd9(PLN)16(OH)10](+), shows a broad emission from a ligand based triplet state with an onset of about 1000 wavenumbers in excess of the europium emission. As supported by photoluminescence lifetime measurements for both complexes, we deduce an efficient europium sensitization via PLN-based triplet states. The luminescence spectra of the complexes are discussed in terms of a square antiprismatic europium/gadolinium core structure as suggested by density functional computations.

Substitutional photoluminescence modulation in adducts of a europium chelate with a range of alkali metal cations: a gas-phase study.

We present gas-phase dispersed photoluminescence spectra of europium(III) 9-hydroxyphenalen-1-one (HPLN) complexes forming adducts with alkali metal ions ([Eu(PLN)3M](+) with M = Li, Na, K, Rb, and Cs) confined in a quadrupole ion trap for study. The mass selected alkali metal cation adducts display a split hypersensitive (5)D0 → (7)F2 Eu(3+) emission band. One of the two emission components shows a linear dependence on the radius of the alkali metal cation whereas the other component displays a quadratic dependence thereon. In addition, the relative intensities of both components invert in the same order. The experimental results are interpreted with the support of density functional calculations and Judd-Ofelt theory, yielding also structural information on the isolated [Eu(PLN)3M](+) chromophores.

Room temperature switching of a neutral molecular iron(II) complex.

Abrupt room temperature switching (T(c) = 295 K with a 5 K hysteresis) was achieved in a neutral Fe(II) complex based on a 2-(1H-pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine ligand. Structural characterization and spin crossover study (via SQUID magnetometry, photoexcitation and X-ray absorption spectroscopy) in the solid state are described.

Substitution-controlled ultrafast excited-state processes in Ru-dppz-derivatives.

Ru-dppz (dppz = dipyrido[3,2-a:2',3,3'-c]phenazine) complexes play an important role as environmentally sensitive luminescence sensors and building blocks for larger supramolecular compounds. Their photophysical properties are known to be highly sensitive to intermolecular solvent-solute interactions and solvent bulk-properties. Here, the synthesis and characterisation of a novel Ru-dppz derivative is reported. The potential of drastically tuning the photophysical properties of such complexes is exemplified, by introducing very simple structural modifications, namely bromine, into the dppz-ligand scaffold. The photophysics i.e. nature of excited states and the excited-state relaxation pathway of the various complexes has been investigated by means of electrochemical measurements, steady-state emission experiments and femtosecond time-resolved spectroscopy. It could be shown that the location of bromine substitution influences the relative energy between a luminescent and a non-luminescent metal-to-ligand charge-transfer state and therefore quenches or facilitates transitions between both. Hence it is illustrated that the luminescent properties and the underlying ultrafast excited-state dynamics of the complexes can be controlled by structural variations, i.e. by intramolecular interactions as opposed to changes in the intermolecular interactions.

Phosphaalkenes in pi-conjugation with acetylenic arenes.

Phosphaalkene inclusion at the periphery of acetylenic arenes results in decreased band gaps of the title compounds as verified by spectroscopic and electrochemical techniques. The electronic coupling between two 1-phosphahex-1-ene-3,5-diyne units is mediated by all para-substituted arenes and increases from 4b to 4d.

C,C-diacetylenic phosphaalkenes as heavy diethynylethene analogues.

A series of C,C-diacetylenic phosphaalkenes 1b-e has been prepared from 1-chloropenta-1,2-dien-4-ynes 6b-e in a reaction with Mes*PCl(2) (Mes* = 2,4,6-((t)Bu)(3)Ph) in the presence of LDA. Under identical conditions, isomeric butadiyne-substituted phosphaalkenes 2c-f can be obtained from 3-chloropenta-1,4-diynes 5c-f. The title compounds represent rare examples of diethynylethenes in which a constituting methylene has been replaced by a phosphorus center. The formation of both isomers can be rationalized by a common pathway that involves isomeric allenyllithium species. Spectroscopic, electrochemical, and theoretical investigations show that the phosphorus heteroatoms are an intrinsic part of the compounds' pi-systems and lead to decreased HOMO-LUMO gaps compared to those in all-carbon-based reference compounds.

Photophysics of an intramolecular hydrogen-evolving Ru-Pd photocatalyst.

Photoinduced electron-transfer processes within a precatalyst for intramolecular hydrogen evolution [(tbbpy)(2)Ru(tpphz)PdCl(2)](2+) (RuPd; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'c:3'',2'',-h:2''',3'''-j]phenazine) have been studied by resonance Raman and ultrafast time-resolved absorption spectroscopy. By comparing the photophysics of the [(tbbpy)(2)Ru(tpphz)](2+) subunit Ru with that of the supramolecular catalyst RuPd, the individual electron-transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. The resonance Raman data reveal that the initial excitation of the molecular ensemble is spread over the terminal tbbpy and the tpphz ligands. The subsequent excited-state relaxation of both Ru and RuPd on the picosecond timescale involves formation of the phenazine-centered intraligand charge-transfer state, which in RuPd precedes formation of the Pd-reduced state. The photoreaction in the heterodinuclear supramolecular complex is completed on a subnanosecond timescale. Taken together, the data indicate that mechanistic investigations must focus on potential rate-determining steps other than electron transfer between the photoactive center and the Pd unit. Furthermore, structural variations should be directed towards increasing the directionality of electron transfer and the stability of the charge-separated states.