Photoinduced energy- and electron-transfer from a photoactive coordination cage to bound guests.

In a coordination cage which contains an array of twelve naphthyl chromophores surrounding a central cavity, photoinduced energy or electron-transfer can occur from the chromophore array to the bound guest in supramolecular host/guest complexes

High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS†

A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power, ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards, in the form of pressed pellets (no binder), were prepared in-house using ferromanganese concentrates from a deep-sea nodule reference material as well as from shallow-marine concretions varying in size and having different proportions of three major phases: aluminosilicates, Fe- and Mn-oxyhydroxides. Element concentrations in each standard were determined by means of conventional solution nebulisation ICP-MS following acid digestion. Examples of selected inter-element correlations in distribution patterns along the cross-section of a concretion are given

Conformation and protonation of 2,2'-bipyridine and 4,4'-bipyridine in acidic aqueous media and acidic ZSM-5 zeolites: A Raman scattering study

In situ FT-Raman scattering spectroscopy was used to monitor the sorption kinetics of 2,2'- and 4,4'-bipyridine in acidic ZSM-5 zeolites. The data processing of all the Raman spectra was applied to extract the characteristic Raman spectra of occluded species and respective Raman contribution generated from many spectral data which resolves spectrum of mixture into pure component spectra without any prior information. The assignment of the extracted spectra was performed according to careful comparison with corresponding spectra extracted from a set of Raman spectra recorded during the protonation of 2,2'- or 4,4'-bipyridine (bpy) in hydrochloric acid aqueous solutions. The data processing of the Raman spectra recorded during the slow sorption of 4,4'-bpy in acidic HnZSM-5 (n = 3, 6) zeolites provides specific Raman spectrum of N,N'-diprotonated dication 4,4'-bpyH22+ as unique species generated in the void space of acidic ZSM-5 zeolites. No evidence of Lewis acid sites was found during the sorption of 4,4'-bpy by Raman scattering spectroscopy. The data processing of the Raman spectra recorded during the slow sorption of 2,2'-bpy in acidic HnZSM-5 (n = 3, 6) zeolites provides specific Raman spectrum of trans-N-monoprotonated cation 2,2'-bpyH+ as major species generated in the void space of acidic ZSM-5 zeolites at loading corresponding to 1 mol per unit cell. The trans/cis interconversion occurs at higher loading even after the complete uptake of the sorbate and indicates some rearrangement in the void space over a long time. The cations were found to be located in straight channels in the vicinity of the intersection with the zigzag channel of the porous materials with the expected conformations deduced from ab initio calculations. However, the motions of occluded species within the channel of ZSM-5 are hindered but remain in the range of the isotropic limit of a liquid at room temperature

A theoretical study of the confinement effects on the energetics and vibrational properties of 4,4′-bipyridine adsorption on H-ZSM-5 zeolite

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Spontaneous Ionization and Electron Transfer of Polyaromatics by Sorption in ZSM-5 Zeolites

This article reviews the recent works of the authors about the spontaneous ionization and subsequent electron transfer of polyaromatic molecules upon sorption into ZSM-5 zeolites. The results demonstrate once again that the tight fit between the size of rod shape polyaromatic molecules and the diameter of the straight channel can stabilize radical cation-electron pairs or electron–hole pairs over long periods. Applying diffuse reflectance UV–visible absorption (DRUVv) spectrometry, Raman scattering spectrometry and continuous wave electron paramagnetic resonance (CW-EPR) we were able to monitor with in situ conditions the sorption and ionization of biphenyl (BP), naphthalene (NPH) and anthracene (ANTH) in ZSM-5 zeolite samples with Mn(AlO2)n(SiO2)96–n composition per unit cell (UC) (n = 0–6.6; M = H+, Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+). Particular emphasis was placed on pulsed electron paramagnetic resonance (EPR) spectrometry, which has shown to be a powerful technique for a new insight of the ejected electron. The spontaneous ionization is an intrinsic property of the inner surface of the porous materials, which depends both on the ionization potential of sorbate and the polarization energy of the host at the sorption site. For molecules with relatively low ionization potential such as ANTH (IP 7.44 eV) the ionization can occur in both dehydrated acidic and non acidic MnZSM-5 (n > 2; M = H+, Li+, Na+, Mg2+, Ca2+) zeolites. However, the ionization yield was found to highly depend on the nature of the extraframework cation and was found to decrease from H+ (100%) > Li+ (30%) ~ Mg2+ ~ Ca2+ >> Na+ >> K+, Rb+, Cs+ (0%). It was established that the ejected electron is trapped as isolated electron in the oxygen framework in close proximity of Al atoms and extraframework cations with some pairing electronic effect with the ANTH•+ radical cation. Calcination of acidic HnZSM-5 under molecular oxygen is a prerequisite for the spontaneous ionization of BP (IP 8.16 eV) and NPH (IP 8.14 eV) with higher ionization potential. The spontaneous ionization of molecules with relatively high ionization potential such as NPH and BP was effective upon sorption after generation of electron acceptor Lewis acid sites. The oxidizing power of radical cations BP•+ and NPH•+ initiates at room temperature subsequent electron abstraction from the framework and generates unusual long-lived electron–hole pairs. The oxidizing power of ANTH•+ is inefficient at room temperature but is effective at 450 K. The electron and positive hole are trapped in the oxygen framework in close proximity of Al and proton with electronic interactions with the occluded sorbate before the final charge recombination. To cite this article: S. Marquis et al., C. R. Chimie 8 (2005)

Solvatochromism and photochromism by zeolite confinement. Salicydeneaniline in MFI-type zeolites

International audienc