Search results for "Absorption"
showing 10 items of 2701 documents
Decoupling the artificial special pair to slow down the rate of singlet energy transfer
2012
Trimer 2, composed of a cofacial heterobismacrocycle, octamethyl-porphyrin zinc(II) and bisarylporphyrin zinc(II) held by an anthracenyl spacer, and a flanking acceptor, bisarylporphyrin free-base ( Ar = -3,5-(t Bu )2 C 6 H 3), has been studied by means of absorption spectroscopy, "steady state and time-resolved fluorescence" and fs transient absorption spectroscopy, and density functional theory (DFT) in order to assess the effect of decoupling the chromophores' low energy MOs on the rate of the singlet, S1, energy transfer, k ET , compared to a recently reported work on a heavily coupled trimeric system, Trimer 1, [biphenylenebis(n-nonyl)porphyrin zinc(II)]-bisarylporphyrin free-base ( A…
Formation of complex defects in Mn c Mg 1–c O and Ni c Mg 1–c O single solid solution
2005
The results of investigation of the fast neutron irradiation and thermal treatment on absorption spectra of single solid solution of MncMg1–cO, NicMg1–cO and MgO crystals are presented. It is shown that at impurity ion concentration larger than 0.1 mass.% a probability of formation of aggregate centers consisting of more than three F+- or F-centers is small. After thermal treatment of MncMg1–cO and NicMg1–cO single solid solution irradiated by fast neutrons additional wide bands are observed. We assume that these additional bands belong to complex centers of Mn3+-VMg and Ni3+-VMg. The mechanisms of bands formation are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Monodisperse Dialkoxy-Substituted Oligo(phenyleneethenylene)s
2006
Individual but connected synthetic routes for the preparation of the all-E-configured 2,5-dipropoxy-substituted oligo(1,4-phenyleneethenylene)s 1a–g were developed. An increasing number of conjugated stilbene units from n = 1 to n = 11 led to a convergent bathochromic shift (Δλ = λ∞ − λ1 = 127 nm) in the UV/Vis absorption. An exponential function for the convergence of the absorption energies (wavelengths) in conjugated systems is proposed. By a simple extrapolation of this function the effective chain length may be determined.
Exciton interactions in self-organised bacteriochlorophyll a - aggregates
2002
Exciton interactions of self-organised bacteriochlorophyll a - aggregates in non-polar solution linked via water and dioxane have been studied. Absorption and CD spectra of the aggregates show large red shifts typical of J-aggregates. Femtosecond excitation of the Qy band of the aggregates is followed by wavelength dependent non-exponential picosecond relaxation and anisotropy decay takes place in subpicosecond time scale. To explain these observations exciton theory and semi-empirical MO/CI calculations, that constitute the basis of the CIEM-approach developed by Linnanto et al. (J. Phys. Chem. B, 1999, 103B, 8739) was used. Structural models of aggregates were created by using the molecul…
Exciton Interactions and Femtosecond Relaxation in Chlorophyll a−Water and Chlorophyll a−Dioxane Aggregates
1998
Chlorophyll a (Chl a) in hydrocarbon solution with a small amount of dioxane or water shows red-shifted absorption bands at 686 nm and at 700 nm (dioxane) and at 745 nm (water), indicative of self-organized aggregate structures in solution. To study the relationship between the structure and spectral properties of the aggregates, several one-dimensional model structures of Chl a−dioxane and Chl a−water aggregates were computed by the molecular mechanics method. Three overall structures ranging from stick to a ring shape were energetically favored for the dioxane system. All these structures contain structural heterogeneity that consists of repeating dimers that further form tetramer substru…
The influence of sigma and pi acceptors on two-photon absorption and solvatochromism of dipolar and quadrupolar unsaturated organic compounds.
2003
Two-photon absorption cross sections delta and solvatochromic properties were determined for a series of quadrupolar and dipolar compounds by using femtosecond excitation in the spectral range between 710 and 960 nm. The compounds investigated were distyrylbenzenes and polyenes bearing appropriate pi or sigma acceptors. The delta values for the centrosymmetric compounds trans, trans- 1,4-bis[2-(2',5'-dihexyloxy)phenylethenyl]-2,3,5,6-tetrafluorobenzene (6), trans, trans-1,4-bis[2-(4'-dibutylamino)phenylethenyl]- 2,3,5,6-tetrafluorobenzene (2), trans, trans-1,4-bis[2-(4'dimethylamino)phenylbutadienyl]- 2,3,5,6-tetrafluorobenzene (7), trans,-trans-1,4-bis[2-(4'-dimethylamino)phenylethenyl]2,5…
Spin crossover in iron(II) tris(2-(2′-pyridyl)benzimidazole) complex monitored by variable temperature methods: synchrotron powder diffraction, DSC, …
2003
Abstract The thermal expansion of the spin crossover system [Fe(pybzim) 3 ](ClO 4 ) 2 · H 2 O (pybzim=2-(2 ′ -pyridyl)benzimidazole) has been determined from powder X-ray data between 50 and 250 K; the wavelength of the synchrotron source was 1.21888(1) A. The unit cell parameters of the triclinic crystal system were a =12.091 A, b =12.225 A, c =14.083 A, α =77.70°, β =80.35°, γ =74.35°, and V =1944.9 A 3 at 250 K. In addition to the linear thermal expansion of the unit cell volume, an extra expansion due to the low-spin (LS) to high-spin (HS) transition is observed. The V ( T ) function shows a sudden increase comparable with the step in the effective magnetic moment at the transition reg…
EXAFS study of the local structure of crystalline and nanocrystalline Y2O3using evolutionary algorithm method
2015
Temperature-dependent local structure and lattice dynamics of yttria (Y2O3) were studied by X-ray absorption spectroscopy. Novel method, which combines the reverse Monte Carlo and evolutionary algorithm techniques, was applied for the analysis of extended X-ray absorption fine structure at the Y K-edge. This approach allowed us to reconstruct 3D atomic structure models of crystalline and nanocrystalline Y2O3.
Modification of LiF structure by irradiation with swift heavy ions under oblique incidence
2013
The structural modifications of LiF irradiated with swift heavy ions under oblique angles have been investigated using AFM, SEM, chemical etching, nanoindentation and optical absorption spectroscopy. LiF crystals were irradiated under incidence angles of 30 and 70 degrees with 2.2 GeV Au (fluence 57?l011 ions-cm2) and 150 MeV Kr ions (fluence 1012?1014 ions?cm?2). Structural study on sample cross-sections shows that two damage regions ? (1) nanostructured zone and (2) dislocation ? rich zone, which are typical for irradiations at normal incidence, appear also in samples irradiated under oblique angles. However in the latter case a more complex structure is formed that leads to stronger ion-…
Properties of small clusters at ionic surfaces: (NaCl)nclusters (n=1–48) at the (100) MgO surface
1995
We have studied the geometry, binding energy, interaction with the surface, barriers for diffusion, optical absorption, and the possibility for their observation using atomic force microscopy of (NaCl${)}_{\mathit{n}}$ clusters (n=1--48) on the (100) MgO surface. We address the questions at which cluster size do the adsorbed molecules lose their identity and how do strained clusters accommodate the strain. The relation between the structure of initial molecular fragments adsorbed at the surface and the structure of the corresponding thick film is discussed. The results are compared with the calculated structures of the free clusters and the experimental data on the molecular-beam epitaxy of…