Splitting Of Absorption Bands Research Articles

A multifunctional stealthy material for wireless sensing and active camouflage driven by configurable polarization

• A multifunctional design with energy absorption, sensing and camouflage functions • Dipole configurations is achieved by the introduction of cobalt ions • The reconfigured dipole relaxation promotes the splitting of absorption bands The dipole species transformation and polarization relaxation configuration are achieved by changing the cobalt ion stoichiometry, which precisely tailors the electromagnetic attenuation performance of bismuth iron cobalt oxide. When the stoichiometric ratio of Fe:Co is 19:1, the optimal reflection loss reaches -60 dB. The high electromagnetic attenuation performance significantly improve the linear sensitivity of the strain response and active customized stealth capability of the designed multifunctional capacitor-like structure. Therefore, the wireless multifunctional design integrates energy attenuaten of electromagnetic wave with the wireless sensing and active camouflage functions for the first time. The work provides an important step for the realization of electromagnetical multifunctional applications including electromagnetic protection and electromagnetic sensing in artificial beings, medical health and even space travel.

Structure, optical and magnetic properties of radical anion, dianion salts and coordination complexes of organic dye 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA)

Reduction of organic dye 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) yields a series of radical anion and dianion salts of PTCDA (1–5). Their formation is accompanied by essential red shift and splitting of absorption bands of pristine PTCDA (493 and 560 nm) which appear nearly in the whole visible range, namely, at 660, 700 and 760–770 nm for the radical anions, and 514–526, 544–569, 633–644 and 700–713 nm for the dianions. Weaker bands are also observed in the NIR range at 954 and 938–940 nm, respectively. Reduction elongates double CO bonds, and the shape of the anions becomes non-planar due to twisting. A dihedral angle between two planar halves of PTCDA increases together with anion charge. The PTCDA•− radical anions form {PTCDA}22− dimers in 1–3 with short interplanar distances of 3.220–3.299 Å. These dimers show intense charge transfer bands at 1460–1480 nm and they are diamagnetic up to 360 K indicating large singlet-triplet energy gap for them. The dianions are diamagnetic in the salts. The PTCDA2− dianion can also form coordination complexes coordinating two potassium cations in {cryptand(K+)}2(PTCDA2−)⋅C6H4Cl2 (6) or vanadocene cation in {cryptand(K+)}(Cp2V+)(PTCDA2−)⋅C6H4Cl2 (7). Mixed {cryptand(K+)}2(PTCDA2−){GaIIICl(Pc•3−)}•−⋅2C6H4Cl2 (Pc: phthalocyanine, 8) salt containing two strongly absorbing anionic chromophores has also been obtained. Both anions are chequered in the layers forming short CO(PTCDA2−)⋅⋅⋅H[GaIIICl(Pc•3−)}•−] hydrogen bonds. Most probably, namely these bonds provide rather effective antiferromagnetic coupling of the [GaIIICl(Pc•3−)}•−] spins (S = 1/2) within the layers with large negative Weiss temperature of −25 K.

A comparative study of porphyrin dye sensitizers YD2-o-C8, SM315 and SM371 for solar cells: the electronic structures and excitation-related properties

Understanding the electronic structures and excitation properties of dye sensitizers has significant importance to improve the photon-energy conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). Here, based upon the results calculated using density functional theory, the electronic structures and excitation related properties of porphyrin dye sensitizers YD2-o-C8, SM315, and SM371 were analyzed. It was found that the similar electronic structures of YD2-o-C8 and SM371 result in similar absorption spectra, excitation, and free energy variation for electron injection (EI) and dye regeneration. However, since the electronic structure of the benzothiadiazole unit is well-coupled to that of the porphyrin ring, introducing benzothiadiazole into porphyrin dyes generates a decrease in the lowest unoccupied molecular orbital energy, red-shift and splitting of absorption bands. Meanwhile, remarkably it increases the transferred charges of excitation, which is responsible for the superior short-circuit current density of SM315 sensitized DSSCs. Furthermore, the transition configurations and molecular orbitals indicate the diarylamine group acts as an electronic donor, and the different EI modes with different timescales coexist in excited states due to the multi-configurations of transition. The results of structure-property relationships are favorable to develop novel dye sensitizers for DSSCs.

Absorption and Fluorescence Spectra of Aqueous Solutions of Disodium Cromoglycate

ABSTRACT In the AM1 approximation, we calculated the molecular geometry and energetic structure of an individual molecule of disodium cromoglycate and its conformers as well as measured their absorption and fluorescence spectra in aqueous solutions of different concentrations. The calculation of electron transitions gives the lowest two π-π* transitions and one n-π* for the unit aromatic chromophore which is slightly split in a cromoglycate dianion containing two aromatic blocks. These transitions are found to correspond to the low intensive absorption band at 330 nm and fluorescence at 384 nm upon low concentration. It is established that the increase in the concentration leads to the aggregation and hence to the essential splitting of absorption bands and appearance of the fluorescence at 485 nm.

Vibrational spectroscopy of a tetraureidocalix[4]arene based molecular capsuleElectronic supplementary information (ESI) available: three tables containing fully assigned IR data of tetraureido calix[4]arene 1, its complex with cyclohexane and benzene, and the corresponding model substances 2–5 as well as 1H NMR spectra of the capsules 1·C6H6·1 and 1·C6H12·1 in solution. See http://www.rsc.org/suppdata/p2/b1/b108055p/

Structural models for self-assembled dimers composed of two urea calix[4]arenes which entrap benzene or cyclohexane are developed using Fourier transform infrared (FTIR) spectroscopy. Based on the host–guest ratio determined by 1H NMR spectroscopy in solution, and confirmed for the solid state by a thermogravimetric analysis, it is possible to prove by a comparison of the FTIR data of host, guest, complex and model compounds, that the capsule is held together by a cyclic array of weak and strong hydrogen bonds between the urea units attached at the wide rim of the calixarenes. The dimerization of the two urea units leads to a loss of symmetry, and an averaged C4 symmetrical arrangement is probable. Guest molecules, such as benzene or cyclohexane, are enclosed inside the container rotating fast on the IR timescale around a longitudinal axis of the guest. From the observed splitting of absorption bands upon dimerization and inclusion it follows that either two crystallographically independent types of capsules exist in the crystal lattice or that the guests are occupying two major orientations in the capsule. As indicated by a higher complexation induced shift for cyclohexane, this guest exhibits a tighter interaction with the host molecules compared to benzene.

Role of Intermolecular Interactions in Forming the Vibrational Spectra of Carbohydrate Nitrate Crystals in the Region 1600–1700 cm−1

To elucidate the role of intermolecular interactions in forming the vibrational spectra of the crystals of carbohydrate nitrates in the region 1600–1700 cm−1, theoretical calculations are performed (in the approximation of an additive model of interatomic interactions with the use of the Green's functions) for the density of vibrational states and the intensity of absorption bands in the IR spectrum of a methyl-β-D-glucopyranoside tetranitrate molecule in a crystal. It is shown that the splitting of absorption bands in the IR spectral region under consideration relates to the crystal effect.

On the splitting of SiH absorption bands in infrared spectra of hydrogenated microcrystalline silicon

Abstract The structure of hydrogenated microcrystralline silicon (mc-Si: H) films deposited by hot-wire chemical vapour deposition was investigated by means of X-ray diffraction (XRD) and infrared (IR) spectroscopy. Roughly random orientation of crystallites grained preferentially by (111) planes was established by XRD. The behaviour of IR absorption lines were analysed with respect to the variation in mean grain sizes and high-temperature treatments. As was established, the characteristic features of IR absorption in mc-Si: H come from the bonding of hydrogen on grain boundaries in the form of monohydrides and polyhydride groups and the splitting of absorption bands. The latter was interpreted in terms of absorption of optically anisotropic SiH monolayers covering the internal surfaces in mc-Si: H.

The splitting of absorption bands in IR spectra of anisotropic SiH monolayers covering the internal surfaces in μc-Si:H

Microcrystalline silicon (μc-Si:H) films with a hardly detectable residual amorphous phase fraction (<5%) have been prepared by hot-wire chemical vapor deposition (HW-CVD). The hydrogen bonding and structure of the internal boundaries in μc-Si:H samples were studied by means of IR spectroscopy. The absorption bands of monohydrides, SiH, and polihydrides, SiH x , were identified with respect to their different thermal stability. A characteristic feature of the IR absorption in μc-Si:H investigated in this paper is the splitting of SiH vibrational modes. The interpretation of this splitting in terms of the absorption of optically anisotropic SiH monolayers covering the internal surfaces in μc-Si:H enables us to identify the absorption lines in IR spectra and to determine the crystallographic orientation of grain boundaries in our μc-Si:H samples.

The spectrochemical properties of bis(amino hydroxamato)copper(II) complexes

The d-d absorption spectra of CuL 2, where L = glycinehydroxamic acid (Glyha), l-α-alaninehydroxamic acid (Alaha), l-α-leucinehydroxamic acid (Leuha), l-histidinehydroxamic acid (Hisha) and sarcosinehydroxamic acid (Sarha), in aqueous solutions have been treated by the Angular Overlap Model (AOM) in C 2 h symmetry. Low symmetry splittings of absorption bands of the measured spectra were found by Gaussian analysis. The ligand field parameters were estimated by the Powell optimize algorithm.

Analysis by exciton theory of the optical properties of the Chloroflexus aurantiacus reaction center

The optical properties of the reaction center of the filamentous green bacterium Chloroflexus aurantiacus, that contains three bacteriochlorophyll (BChl) a and three bacteriopheophytin (BPh) a molecules, were analyzed in the near-infrared region with the aid of exciton theory. The coordinates obtained from the X-ray analysis of the reaction center of Rhodopseudomonas viridis (Deisenhofer, J., Epp, O., Miki, K., Huber, R. and Michel, H. (1984) J. Mol. Biol. 180, 385–398) were used for the geometry of the reaction center of C. aurantiacus, with the replacement of one of the ‘accessory’ BChl molecules by BPh. The results were found to be in good agreement with experimental low-temperature absorption spectra, linear and circular dichroism and fluorescence polarization spectra and lead to the following conclusions. The allowed, low-energy exciton transition of the primary electron donor (P-865) is located at 887 nm and carries the dipole strength of approx. two BChl a monomers; the high-energy exciton transition, around 790 nm, is mixed with wave functions of other pigments, which explains its relatively small angle with respect to the 887 nm transition. The optical transition of the accessory BChl a molecule near 812 nm has some contribution of the BChls that constitute P-865. This can account for the experimentally observed reorientation and shift of this transition upon oxidation of P-865. Two of the BPh molecules are located on the same (probably the M) polypeptide subunit and show a clear splitting of absorption bands (11 nm) due to exciton coupling; the single BPh on the opposite branch shows hardly any exciton shift. Similar calculations for reaction centers of purple bacteria that contain four BChl a and two BPh a molecules resulted in a very low dipole strength for the high-energy transition of the primary donor due to antisymmetric mixing with both accessory BChl a wave functions and gave very little splitting of the absorption bands of BPh a. Our results indicate that the arrangement of the chromophores in reaction centers of C. aurantiacus is very similar to that in purple bacteria. The functional L-chains of the reaction centers of purple and filamentous green bacteria consist of pigments of the same type in a probably very similar arrangement.

Singly and Doubly Excited States of Exchange-Coupled Dimers

Abstract The optical absorption spectra of dimers of weakly coupled paramagnetic transition metal ions differ from those of monomelic complexes in several respects: They show additional splittings of absorption bands; intensities of spin-forbidden transitions may be enhanced by several orders of magnitude; the dimer absorptions may be strongly temperature dependent; new bands corresponding to the simultaneous excitation of both ions are observed. From an analysis of excited state exchange splittings, the orbital contributions to the exchange parameter JAB can be deduced. The dimer excitations are intimately related to charge transfer transitions, which provide their intensities.

Charge-Transfer Complexes of Carbonyl Cyanide in Gas and Condensed Phases

Absorption spectra of carbonyl cyanide charge-transfer complexes with common donors were studied in gas phase and in solutions, their fluorescence spectra in n-hexane solutions at 77°K. The general form of the absorption band is the same in the gas and liquid phases, but the gas-phase spectra show a blue shift of 2000–3500 cm−1, an intensity decrease, and a strong increase in the equilibrium constant of complex formation. The reasons of the frequency shift, the splitting of absorption bands, and the influence of complex formation on the electronic spectrum of carbonyl cyanide are discussed.

Studies of the birefringence and birefringence dispersion of polypeptides and proteins.

AbstractAn apparatus has been constructed which permits the polarimetric observation of streaming solutions of macromolecules. The apparatus is a streaming birefringence device allowing the usual measurements of birefringence parallel to the cylinder axis but which in addition transmits light in the radial direction. Installation of the apparatus between the polarizer and analyzer of a Rudolph polarimeter makes possible the measurement of changes in optical rotation, dichroism and birefringence. The present work is concerned with the latter effect. The systems studied were α‐helical polyglutamic acid, paramyosin, and collagen (ichthyocol). The combined measurements of radial and axial birefringence completely determines the refractive index ellipsoid of the streaming fluid. This result in turn permits the testing of the Peterlin‐Stuart distribution function for streaming in a Couette device, apart from a proportionality constant. The comparison between theory and experiment is very satisfactory provided the system is reasonably homogeneous with regard to molecular length and is sufficiently dilute. On the other hand, it is concluded that the Peterlin‐Stuart optical factor seriously overestimates the “form” birefringence in agreement with recent results and conclusions of Taylor and co‐workers. The apparatus permits the study of the dispersion of the birefringence in the radial direction. The dispersion of collagen follows a one‐term Sellmeier formula and is dominated by absorption bands in the neighborhood of 2000 A. On the other hand, the dispersion of the α‐helical systems is complex and requires a multiterm Sellmeier formula. This contrast between the two kinds of polypeptidc helices is similar to results obtained with other optical techniques and is attributed to the splitting of absorption bands in the α‐helix.