Absorption Spectra Of Single Crystals Research Articles

Azobased iminopyridine ligands and their rhenium metal complexes: Syntheses, spectroscopic, trans-cis photoisomerization and theoretical studies

The reaction of rhenium(I) pentacarbonyl chloride Re(CO)5Cl with N,N-dimethyl-4-((E)-(pyridin-2-ylmethylene) amino)phenyl) diazenyl) aniline L1 and (E)-4-((E)-(4-nitrophenyl)diazenyl)-N-(pyridin-2-ylmethylene) aniline L2 affords two rhenium metal complexes [ReL1(CO)3Cl] (ReL1) and [ReL2(CO)3Cl] (ReL2), respectively. These Re(I) complexes were characterized in detail, including their single crystal structures, absorption spectra and electronic structures using DFT calculations. Trans to cis photoisomerization of the free ligands and complexes was investigated experimentally and rationalized theoretically. Interestingly, light-induced photoisomerization of the azo fragment is observed for free ligand L1 while inhibition of this process is produced upon coordination to Re metal cation.

Spectral Characteristics of Mn2+ Doped Na5Lu9F32 Single Crystals

Mn2+ ion doped Na5Lu9F32 single crystals are grown by an improved Bridgman method. The absorption and fluorescence spectrum of single crystals in the range of 300–800 nm are measured to investigate the spectral properties. Fluorescent band centered at 550 nm was observed in the fluorescence spectrum of the crystals corresponding to the 4T1(4G) → 6A1(6S) transition of the Mn2+ ion. An excitation peak of 400 nm is observed in the excitation spectrum due to the charge transfer transition of electrons from the ground state to the conduction band. The calculated values for the crystal field (Dq) and Racah parameters indicate that a stable cubic crystal structure of Mn2+ ion surrounded by eight F− ligands can be formed with the introduction of Mn2+ ion into Na5Lu9F32 single crystals.

Crystal structure of Ce-doped (La,Gd)2Si2O7 grown by the Czochralski process

Single crystals of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 were grown by the Czochralski method. Structure analysis of the single crystals by X-ray diffraction (XRD) revealed that (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 crystalize in monoclinic cells (space group P21/c), a = 5.3905(8) Å, b = 8.5605(11) Å, c = 13.957(2) Å, β = 112.223(6)º, and a = 5.3921(7) Å, b = 8.5688(10) Å, c = 13.9172(14) Å, β = 111.980(5)º, respectively. One of the two different rare-earth sites is preferentially occupied by La and Gd atoms or by La, Ce and Gd atoms, and the other is occupied by Gd atoms only. Peaks attributed to the 4f-4f transitions (8S7/2–6G7/2 and 8S7/2–6Ix) of Gd3+ and 4f-5d transitions of Ce3+ were observed in the absorption spectra of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 single crystals.

Expanding pentafluorouranates: hydrothermal synthesis and characterization of β-NaUF5 and β-NaUF5·H2O.

Two new sodium uranium(iv) pentafluorides were synthesized from uranium dioxide, HF, and NaF using mild hydrothermal conditions. β-NaUF5·H2O has greater lattice energy than previously-known α-NaUF5·H2O and possesses lower symmetry with the latter compound being orthorhombic, whereas β-NaUF5·H2O is monoclinic. Trigonal β-NaUF5 also possesses different connectivity between the [UFn] building units than the α-phase, with higher symmetry and greater lattice energy than orthorhombic α-NaUF5. The single crystal absorption spectra of these compounds are also reported and compared.

Preparation, single-crystal investigation and spectrophotometric studies of proton transfer complex of 2,6-diaminopyridine with oxalic acid in various polar solvents

Charge transfer complex (CT complex) of donor, 2,6-diaminopyridine (DAP) and π- acceptor, oxalic acid (OA) has been synthesized in acetonitrile at room temperature. The CT complex is formed through the transfer of lone pair electrons from 2,6-diaminopyridine to oxalic acid. The CT complex was characterized by elemental analysis, FTIR spectra single crystal studies, TGA-DTA, 1H NMR and electronic absorption spectra in different solvents which indicate the CT interaction associated with proton migration from the acceptor to the donor followed by hydrogen bonding via N+H⋯O−. It was found that formation of CT Complex is solvent dependent. Spectrophotometric data show the properties of complex in terms of formation constant (KCT), molar extinction coefficient (εCT), energy of interaction (ECT), ionization potential (ID), resonance energy (RN), free energy (ΔG), oscillator strength (f) and transition dipole moment (μEN). The stoichiometry of the CT complex was found to be 1:1 by a straight-line method between donor and acceptor with maximum absorption bands. The physical parameters of CT complex were evaluated by the Benesi–Hildebrand equation. The agreements between the spectroscopic results were also confirmed by single crystal X-ray of the resulting charge transfer complex.

Optical absorption and photoconductivity of MnGaInS4 single crystals in polarized light

The results of studying optical-absorption and spectral curves of photoconductivity in MnGaInS4 single crystals are presented for two light polarizations (E || C and E ⊥ C). The intrinsic absorption edge and the band-gap width of MnGaInS4 single crystals in polarized light are determined. The anisotropy of optical absorption and photoconductivity spectrum of MnGaInS4 single crystals is observed. It is suggested that the polarization splitting of the absorption edge is related to the splitting of the MnGaInS4 valence band.

One-Pot Synthesis of a Mono-O,B,N-strapped BODIPY Derivative Displaying Bright Fluorescence in the Solid State.

Tin(IV) catalysis allows isolation of a boron dipyrromethene derivative bearing a solitary strap around the boron center. The conditions favor internal cyclization without contamination by side products and provide high yields of product in good purity. A phenolate-based strap imposes chirality and causes geometrical distortion of the dipyrrin. Relatively strong fluorescence is observed for single crystals, evaporated films, and adsorbed layers. Single-crystal absorption and emission spectra resemble those observed from solution with contributions from a dimer.

Spin-state-correlated optical properties of copper(ii)-nitroxide based molecular magnets.

Molecular magnets based on copper(ii) ions and stable nitroxide radicals exhibit promising switchable behavior triggered by a number of external stimuli; however, their spin-state-correlated optical properties vital for photoinduced switching have not been profoundly investigated to date. Herein, the electronic absorption spectra of single crystals of three representatives of this unique family are studied experimentally and theoretically in the visible and near-IR regions. We established that the color of the complexes is mainly determined by optical properties of the nitroxide radicals, whereas the Cu(hfac)2 fragment contributes to the near-IR range with the intensity smaller by an order of magnitude. The thermochromism of these complexes evident upon thermal spin state switching is mainly caused by a spectral shift of the absorption bands of the nitroxides. The vibrational progression observed in the visible range for single crystals as well as for solutions of pure nitroxides is well reproduced by DFT calculations, where the C-C stretching mode governs the observed progression. The analysis of the spectra of single crystals in the near-IR region reveals changes in the energy and in the intensity of the copper(ii) d-d transitions, which are well reproduced by SOC-NEVPT2 calculations and owe to the flip of the Jahn-Teller axis in the coordination environment of copper. Further strategies for designing bidirectional magnetic photoswitches using these appealing compounds are discussed.

IR absorption spectra in the region of stretching and deformation vibrations of hydrogen bond in pure and alloyed single crystals of LiNbO3

We have measured infrared absorption spectra of the stretching and bending vibrations of the hydrogen bond of pure and alloy additives Me (Me = Mg, Zn) single crystals of lithium niobate (LiNbO 3 ) grown using various technologies. Preliminary studies of the spectra showed that the frequency of stretching vibrations in the IR spectra of single-crystal samples obtained from the homogeneously doped charge differ significantly (more than 50 cm −1 ). However, no difference in the IR spectra of single crystals obtained using other doping techniques, we have found. It is assumed that the observed differences in the absorption spectra of single crystals due to the different character of the formation of hydrogen bonds in the preparation of precursors Nb 2 O 5 : Me.

(Invited) Anisotropic Magnetism of an Endohedral Metallofullerene for Molecular Location Sensor

Location recognition in molecular-scale provides valuable information on positional relationship, absolute conformation and dynamics of molecules. They can be used for deep understanding of nature of functional molecular materials or for elucidating biological processes. Therefore, a number of molecular probes have been developed and reported to date for molecular recognition and location determination. Recently, our group has reported anisotropic magnetism of an endohedral metallofullerene (EMF) Ce@C82 both in a pristine form and chemically functionalized form.1,2 Remarkably, the anisotropy of the magnetism which is led by the encapsulated Ce atom was slightly influenced by the carbene addition reaction. In addition, absolute position of the hydrogen atoms of the addend were assigned by the difference in the effective distance of the anisotropic magnetism, which is decreased with the cube of distance between the Ce and hydrogen atoms. In this study, we have developed Ce@C82 derivatives that demonstrate a potential of EMFs for location recognition in molecular-scale. Five derivatives of Ce@C82 were successfully synthesized and isolated by a similar radical reaction that we reported recently.3 Addition position of the two isomers of them were unambiguously determined by a single crystal structure and/or characteristic absorption spectra. DFT calculations provide reasonable criteria to predict the addition position by the radical coupling reaction. The carbon atoms that have high SOMO density and positive charge are preferable for the addition position. Temperature-dependent 1H-NMR measurements demonstrated unique paramagnetic shifts that are derived by the anisotropic magnetism of the Ce atom. And further analysis of the shifts revealed the dependency of the shift based on the distance and relative position from the Ce atom. This result indicates that the paramagnetic shifts provide location information of the addend. Therefore, Ce@C82 is capable to act as an molecular probe for location recognition of atoms by utilizing anisotropic magnetism of an EMF. Reference: 1. T. Wakahara et al. J. Am. Chem. Soc. 2004, 126, 4883-4887. 2. Y. Takano et al. J. Am. Chem. Soc. 2009, 131, 9340-9346. 3. Y. Takano et al. J. Am. Chem. Soc. 2008, 130, 16224-16230.

Excitonic emission and absorption resonances in V0.25W0.75Se2 single crystals grown by direct vapour transport technique

A systematic study on emission and absorption spectra of vanadium mixed tungsten diselenide single crystals grown by direct vapour transport (DVT) technique is reported. The grown crystals were characterized by energy dispersive analysis of X-ray (EDAX), which gives the confirmation about the stoichiometry. The structural characterizations were accomplished by X-ray diffraction (XRD), surface morphology and transmission electron microscopy (TEM). These characterizations were indicating the growth of V0.25W0.75Se2 single crystal from vapour phase. The optical response of this material has been observed by combination of UV–vis-NIR spectroscopy and photo luminescence (PL) spectroscopy. A detailed study of excitonic emission and absorption resonances was carried out on grown crystals. The energy band gap was calculated for indirect allowed transition with absorbed and emitted phonon. Additionally, absorption tail for grown crystal is found to obey the Urbach׳s rule.

IR absorption and Raman spectra of single crystals of stable germanium isotopes

The Raman and IR absorption spectra of single crystals of germanium isotopes 72Ge, 73Ge, 74Ge, and 76Ge in the region of phonon absorption and interband electronic transitions are studied at room temperature. The dependence of the Raman peak position on the atomic mass has the form ν ~ M –1/2. The shifts of the phonon absorption peaks of individual isotopes with respect to germanium of natural isotopic composition natGe are determined. With increasing average atomic mass of germanium, these peaks shift to longer wavelengths. In the region of interband electronic transitions, the intrinsic absorption edge of 76Ge is observed to shift by 1 meV to higher energies with respect to Ge of natural isotopic composition. For isotopes with atomic masses close to that of natural germanium (72Ge,73Ge, 74Ge), we found no significant difference in the band gap width at room temperature.

Absorption and luminescence spectra of CeF3-doped BaF2 single crystals and nanoceramics

We have studied the radiation resistance of BaF2:Ce3+ scintillator single crystals and ceramics at gamma doses from 106 to 108 rad. It has been shown that the ceramics produced using the self-fluorinating precursor BaF2 ∙ HF is more radiation-resistant.

Synthesis and thermal, optical, dielectric and mechanical properties of l-asparagine sodium nitrate single crystal

Single crystal of l-asparagine sodium nitrate (LASN) was grown from aqueous solution by room temperature solution growth technique. The grown crystal was characterized by single crystal X-ray diffractometry (XRD), FTIR and optical absorption spectrum. The micro hardness test of the sample revealed that the crystal belongs to the soft category of materials. The dielectric response of the crystal with varying frequencies was studied and reported. The thermal stability of the compounds has been determined by TG-DTA curves. The SHG relative efficiency of LASN crystal was found to be inferior than that of KDP.

Study on a series of rhenium complexes: Synthesis, characterization, photophysical feature and oxygen sensing performance

This paper synthesized a series of diamine ligands with different conjugation chains and their corresponding Re(I) complexes for oxygen sensing purpose. It was anticipated that these conjugation chains might increase sensing collision probability and thus improve sensing performance. These Re(I) complexes were characterized in detail, including their single crystal structures, electronic transitions, absorption and emission spectra, emission lifetimes and yields. By doping them into a silica substrate MCM-41, their emission response to various O2 concentrations was analyzed. A maximum emission intensity ratio of 8.17 was obtained with short response time of 7s. The correlation between sensing performance and probe structure was discussed tentatively. We finally came to a conclusion that excited state lifetime was a major factor controlling sensitivity. While electron distribution effect on sensitivity was limited.

Investigation on growth and defects of Ho3+:BaY2F8 crystals grown by Czochralski method

Large and heavily Ho3+-doped BaY2F8 single crystals were grown by the Czochralski method. X-ray powder diffraction was applied to analyze the phase of the crystal samples. Simultaneously, metallographic microscope, scanning electron microscopy and energy dispersive spectrometer were employed to observe and investigate defects in the as grown crystals. Two significant kinds of defects, namely cracking and impurities were discovered in the samples of Ho3+:BaY2F8 single crystals. Theoretical analyses suggested that mechanisms concerning the formation of the impurities such as bubbles and inclusions were considered to be closely related to the growth temperature and atmosphere while the former defect was primarily brought by the lattice distortion relating to the thermal stress and the impurities. Based on the results of experiments and theoretical analyses, the parameters of growth process were optimized and a crack free 20 mol% Ho3+:BaY2F8single crystal has been successfully obtained. Furthermore, the UV–Vis-IR (0.2–10 μm) absorption spectra of BaY2F8 single crystal and the crystal heavily doped with Ho3+ ions (20 mol%) have been investigated at room temperature.

Crystal structure of the charge-transfer complex 2-(1,2,3,4-tetra-hydro-naph-thal-en-1-yl-idene)hydrazinecarbo-thio-amide-pyrazine-2,3,5,6-tetra-carbo-nitrile (2/1).

The reaction of 2-(1,2,3,4-tetra­hydro­napthalen-1-yl­idene)hydrazinecarbo­thio­amide (TTSC) with pyrazine-2,3,5,6-tetra­carbo­nitrile (tetra­cyano­pyrazine, TCNP) yields the title 2:1 charge-transfer adduct, 2C11H12N3S·C6N8. The complete TCNP mol­ecule is generated by a crystallographic inversion centre and the non-aromatic ring in the TTSC mol­ecule adopts an envelope conformation with a methyl­ene C atom as the flap. In the crystal, the thio­semicarbazone mol­ecules are connected through inversion-related pairs of N—H⋯S inter­actions, building a polymeric chain along the b-axis direction. The TCNP mol­ecules are embedded in the structure, forming TTSC–TCNP–TTSC stacks with the aromatic rings of TTSC and the mol­ecular plane of TCNP in a parallel arrangement [centroid–centroid distance = 3.5558 (14) Å]. Charge-transfer (CT) via π-stacking is indicated by a CT band around 550 cm−1 in the single-crystal absorption spectrum.

Tetrathiafulvalene-supported triple-decker phthalocyaninato dysprosium(III) complex: synthesis, properties and surface assembly.

Self-assembly of functional compounds into a prerequisite nanostructure with desirable dimension and morphology by controlling and optimizing intermolecular interaction attracts an extensive research interest for chemists and material scientist. In this work, a new triple-decker sandwich-type lanthanide complex with phthalocyanine and redox-active Schiff base ligand including tetrathiafulvalene (TTF) units has been synthesized, and characterized by single crystal X-ray diffraction analysis, absorption spectra, electrochemical and magnetic measurements. Interestingly, the non-centrosymmetric target complex displays a bias dependent selective adsorption on a solid surface, as observed by scanning tunneling microscopy (STM) at the single molecule level. Density function theory (DFT) calculations are utilized to reveal the formation mechanism of the molecular assemblies, and show that such electrical field dependent selective adsorption is regulated by the interaction between the external electric field and intrinsic molecular properties. Our results suggest that this type of multi-decker complex involving TTF units shows intriguing multifunctional properties from the viewpoint of structure, electric and magnetic behaviors, and fabrication through self-assembly.

Calix[4]arene-Supported Mononuclear Lanthanide Single-Molecule Magnet

Three new single paramagnetic lanthanide-based complexes, [Ln(L)(LOEt)] (Ln(3+) = Dy(3+), Tb(3+), and Ho(3+)), are synthesized with the multidentate calix[4]arene ligand H2L (H2L = 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-dihydroxy-26,28-dimethoxycalix[4]arene) and Kläui's tripodal ligand LOEt(-) (LOEt(-) = (η(5)-cyclopentadienyl)tris(diethylphosphito-p)cobaltate(III)). All of the complexes have been characterized by single crystal X-ray diffraction analysis, thermal stability, absorption spectra, and magnetization measurements. The magnetic properties and magnetostructural correlation in this seven-coordinated system are investigated. The dysprosium complex 1 shows typical single-molecule magnetic behavior with characteristic magnetic hysteresis loops and the slow relaxation of magnetization.

Spectroscopy of BODIPY in solid phase: crystal and nanoparticles

We compare the absorption and fluorescence spectra of single crystals and suspensions of nanoparticles with the prediction of the Frenkel theory. The single crystals of a novel synthesized fluorescent BODIPY derivative dye, adamantyl mesityl BODIPY (4,4-difluoro-3,5-di-(adamantyl)-8-mesityl-4-bora-3a,4a-diaza-s-indacene), have been prepared. Their birefringence and dichroism have been studied. The X-ray crystallography shows a monoclinic crystal with all transition moments parallel to one common plane. The refractive indices along the two neutral axes have been measured for a wavelength from 530 to 700 nm, with a difference, Δn equal to 0.11. The Frenkel exciton theory was used here to describe the coupling of the electronic excited states in the crystals. The coupling estimated by the dipolar approximation was compared with the excited state splitting calculated by TDDFT in dimers. A perfect crystal absorption spectrum is predicted. The spectral broadening that occurs at room temperature is also taken into account. The absorption spectrum of the monocrystal is reproduced without adjustable parameters. But we had to take into account the presence of optical leaks in our microspectrophotometer before comparing experiment and theory. The controlled size nanoparticles (NPs) produced by our 3D hydrodynamic focusing microfluidic system exhibit molecule like absorption. We could reproduce their absorption and fluorescence spectra assuming a strong disorder in the Frenkel model. We conclude that the nanoparticles are amorphous.