Spectral Characteristics of C60-Conducting Polymer Junctions: Various Molecular D-A Type Photocells

Abstract

We have found recently that thin film layered heterojunction between C₆₀ and conducting polymer, like poly(3-alkylthiophene) (PAT) shows a photovoltaic effect due to photoinduced charge transfer at the interface. Here we describe two other examples of such photocells in RO-PPV/C₆₀ and PPP/C₆₀ heterojunctions and study their spectral characteristics. Contrary to conventional inorganic semiconductor p-n junction photocells, the C₆₀-PAT junction can be rather viewed as molecular donor-acceptor (D-A) type photocell in which the processes of photogeneration and separation of charge carriers are quite distinct. In a p-n junction free electron-hole pairs are known to be primarily photogenerated at interband transition and then separated in the internal electric field of the barrier, while in D-A molecular photocell mainly neutral excitons are first created by light, with charges being primarily separated at the narrow interface region due to D-A type intermolecular charge transfer interactions. We analyze how this processes depend on the wavelength of the pumping light and on the polarity and magnitude of the applied voltage.     

First crystal structure of a pentacyclic biomarker: 4,4,6a,12b,14b-Pentamethyl-1,2,3,4,4a,5,6,6a,6b,7, 8,12b,13,14,14a,14b-hexadecahydropicen-3β-ol

The crystal structure of the title compound (1, C₂₇H₄₀O 1/8 H₂O) synthesized via photo-induced electron transfer promoted biomimetic cascade cyclization, is reported. Compound 1 crystallizes in the monoclinic space group C2/c, with cell parameters a = 53.982(4), b = 7.1889(6), c = 11.170(1) Å, = 96.86(1). The structure adopts a fully trans-fused ring junction with all methyl groups axially oriented. The geometrical aspects associated with 1 were discussed and compared with the previously determined X-ray data for structurally analogous compounds.     

Molecular and crystal structures of decamethylruthenocene (η5-C5Me5)2Ru in the temperature range 153–300 K: Thermal motion in a crystal according to X-ray diffraction data

The crystal structure of decamethylruthenocene (η⁵-C₅ Me ₅)₂Ru (I) is investigated by X-ray diffraction. It is demonstrated that the compound studied crystallizes in two polymorphic modifications, namely, modification Ia with space group P2₁/m (Z = 2) in the temperature range 153–300 K and modification Ibwith space group P2₁/n (Z = 4) at 203 K. No temperature phase transition between the modifications is found. In crystal Ia, the molecule occupies a special position in the mirror plane. In crystal Ib, the molecule is located in the general position. The cyclic ligands η⁵-C₅ Me ₅, (Cp*) are aligned parallel to each other and adopt an eclipsed conformation. The bond lengths in compounds Ia and Ib are identical. Analysis of the anisotropic displacement parameters of the atoms indicates that molecules Ia and Ib are not structurally rigid and that the Cp* rings involved in these molecules can execute independent librations. In the temperature range 153–300 K, the Cp*(1) ligand in molecule Ia is statically disordered over two positions. The barrier heights B ₅ for rotation of the Cp* ligands are estimated both from the root-mean-square amplitudes of librations 〈ϕ²〉 and with the use of the atom-atom potential method. __________ Translated from Kristallografiya, Vol. 48, No. 2, 2003, pp. 283–292. Original Russian Text Copyright ? 2003 by Zanin, Antipin.     

Arrangement of K Clusters in the K-Doped Zeolite K-LTA

Abstract

K clusters incorporated into zeolite K-LTA causes ferromagnetism below 8 K. Distribution of K⁺ ions in its α-cages was studied by X-ray powder diffraction. On the basis of space group F23, electron-density distribution was determined by Rietveld analysis followed by iteration of analysis by a maximum-entropy method and whole-pattern fitting. K⁺ ions were located in α-cages in such a way that K clusters between adjacent α-cages are not equivalent to each other, which will lead to the ferromagnetism with antiferromagnetic components.     

Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline I I I. p-n-Hexyloxybenzyl ideneam i no-p'-fluorobenzene (HBAF)

Abstract

The heat capacity of HBAF has been measured between 15 K and 385 K. Four phase transitions were found at 328.07 K (crystal-smectic B); 330.33 K (smectic B-smectic A); 334.88 K (smectic A-nematic); and 336.33 K (nematic-isotropic liquid), respectively. The enthalpies and entropies of these transitions were determined to be 23.22 kJ mol^?1/70.7 JK^?1 mol^?1; 3.05/9.2; 3.41/10.2; and 1.17/3.5, respectively. The total transition entropy of HBAF agreed well with those previously reported for the present homologues. The standard thermodynamic functions were estimated up to 385 K. The heat capacity curve of HBAF in the transition region had a close resemblance to that of p-n-hexyloxybenzylideneamino-p'-chlorobenzene. The entropies of the smectic A-nematic and nematicisotropic liquid transitions were compared with those theoretically derived by McMillan. The smectic B-smectic A transition entropy was interpreted in terms of order-disorder phase transition associated with the orientation of molecule.     

Mössbauer Spectra of FePS3-Cobaltocene Intercalation Compound

Abstract

Mössbauer spectra of the FePS₃-cobaltocene intercalation compound were measured in the temperature range of 300K to 10K. The spectra, distinct from those of pure FePS₃, suggest the charge transfer from cobaltocene to Fe-S antibonding orbitals of the FePS₃ host lattice.     

Magnetic Properties Near the Ferromagnetic-Nonferromagnetic Phase Boundary in Potassium Clusters Incorporated into Zeolite LTA

Abstract

Magnetic and optical properties are investigated for K clusters incorporated into zeolite LTA at loading densities of K atoms, n, between 1.0 and 3.2 per cluster. No magnetic ordering is observed at n < 2. The spontaneous magnetization due to ferromagnetism is observed suddenly at n > 2. It is confirmed that the 1p-like quantum electronic state of K cluster plays an essential role in the ferromagnetic phase.     

Supramolecular Association in the Structure of 2,9-<Emphasis Type="Italic">C</Emphasis>-<Emphasis Type="Italic">meso</Emphasis>-2,5,5,7,9,12,12,14-Octamethyl-1,8-diaza-4,11-diazoniacyclotetradecane as its Bis(nitrate) and Bis(acetate) Trihydrate

Abstract In the crystal structure of the nitrate salt, columns of di-cationic macrocycles, each disposed about a center of inversion, are interspersed by pairs of nitrate anions that form charged-assisted N–H···O hydrogen-bonding interactions, reinforced by C–H···O contacts. The topology of the resulting supramolecular architecture is that of a linear chain and these associate via further weak C–H···O contacts. In the structure of the acetate trihydrate, di-cationic macrocycles are circumscribed by 32-membered rings defined by O–H···O interactions, involving the acetate anions and solvent water molecules. Systematic variations in the geometric parameters in the molecular structures are correlated with the influence of intermolecular interactions. The nitrate crystallizes in the monoclinic space group P2₁/n with a = 8.3524(11) ?, b = 12.5497(16) ?, c = 11.1208(16) ?, β = 103.180(3)°, and Z = 2. The acetate trihydrate also crystallizes in the monoclinic space group P2₁/n with a = 9.6679(15) ?, b = 15.278(2) ?, c = 9.8376(18) ?, β = 106.068(5)°, and Z = 2. Index Abstract Supramolecular Association in the Structure of 2,9- C-meso -2,5,5,7,9,12,12,14-Octamethyl-1,8-diaza-4,11- diazoniacyclotetradecane as its Bis(nitrate) and Bis(acetate) Trihydrate Saroj K. S. Hazari, ⁽¹⁾ Tapashi G. Roy, ^(1)* Kanak K. Barua ⁽¹⁾ and Edward R. T. Tiekink ^(2)* A linear supramolecular chain stabilized by charge-assisted N–H···O hydrogen-bonding interactions is found in the nitrate salt. In the acetate trihydrate, di-cationic macrocycles are circumscribed by 32-membered rings constructed by O–H···O hydrogen-bonds. Supramolecular Association in the Structure of 2,9- C-meso -2,5,5,7,9,12,12,14-Octamethyl-1,8-diaza-4,11- diazoniacyclotetradecane as its Bis(nitrate) and Bis(acetate) Trihydrate Saroj K. S. Hazari, ⁽¹⁾ Tapashi G. Roy, ^(1)* Kanak K. Barua ⁽¹⁾ and Edward R. T. Tiekink ^{(2)* (1)}Department of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh ⁽²⁾Department of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249-0698 Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

A pure reentrant cholesteric phase

Abstract

An optically active derivative of p-cyanobiphenyl exhibits a stable reentrant cholesteric phase with the seuqnce: K N?S_A N?I.     

X-Ray Diffraction and Physical Properties of Potassium Fullerides KxC70

Abstract

X-ray diffraction and magnetic-susceptibility measurements have been carried out for single phase K_xC₇₀ (x=1, 3, 4, 6 and 9) compounds synthesized by heating stoichiometric amount of K₉C₇₀ and C₇₀. The x-ray diffraction profiles show no structural transition down to 10K. The fairly large temperature-independent paramagnetic contribution was observed in x=3 and 4. The electrical resistivity has been measured for K evaporated C₇₀ film with increasing K thickness. Two resistivity minima were observed at x=1 and 4.     

Crystal structure and phase transitions in the new crystals of [(CH3)2NH2]2CuCl4[(CH3)2NH2]Cl

Crystals grown from a solution of dimethylammonium and copper chlorides are studied using electron paramagnetic resonance (EPR) and X-ray diffraction. The dielectric properties of the crystals grown are measured. It is established that the crystals have the composition [(CH₃)₂NH₂]₂CuCl₄[(CH₃)₂NH₂]Cl and, in phase I at room temperature, are described by the orthorhombic space group Pna2₁ with the unit cell parameters a = 11.338 Å, b = 9.981 Å, and c = 15.675 Å. At temperatures of 279 K and 253 K, the crystals undergo jumpwise phase transitions into the incommensurate modulated ferroelectric phase II and commensurate modulated phase III, respectively. __________ Translated from Kristallografiya, Vol. 49, No. 1, 2004, pp. 92–100. Original Russian Text Copyright ? 2004 by Kirpichnikova, Pietraszko, Bednarski, Waplak, Sheleg. Dedicated to the 80th Birthday of L.A. Shuvalov     

Influence du Nombre de Chaînes Latérales sur les Propriétés Mésogènes de Dérivés Porphyriniques

Abstract

A number of solid state organic solar cells have been prepared and tested in simulated sunlight. Photovoltaic effects were consistent with the formation of a rectifying junction at the interface between a triphenylmethane dye (n-type) and a merocyanine dye (p-type). The most efficient device consisted of a sandwich of thin layers of indium-tin oxide/malachite green/a benzothiazole-rhodanine merocyanine/Au on Pyrex. Exposure of the cell to chlorine vapour in the absence of air improved the sunlight efficiency to 0.12%. Investigations of the photocurrent action spectrum, rectification and capacitance have given mechanistic information on the photovoltaic energy conversion processes.     

Measurements of Soliton Trapping and Motion in Trans-Polyacetylene Using Dynamic Nuclear Polarization

Abstract

The motion of solitons in undoped trans-(CH)_x is studied over the temperature range 1.5–300 K using dynamic nuclear polarization. The results of a theoretical model for the combined solid state and Overhauser effects in terms of the time dependence of the electron nuclear interaction due to motion of electrons is presented. Its application to the experiment shows that most of the solitons are trapped below 30 K and that the mobile solitons above 30 K have a diffusion coefficient that is approximately proportional to the square root of the temperature. At 300 K the time for a soliton to diffuse its length is greater than or equal to 1.7 × 10^?11 seconds.     

Physical Properties of Vanadium Oxide Bronzes β-A0.33V2O5 (A = Ca and Sr)

Abstract

The vanadium bronzes.β-A_0.33V₂O₅(A= Ca and Sr) have been synthesized, and their electromagnetic properties investigated. They show phase transitions at 150K and 170K, respectively, accompanying with anomalies in the magnetic susceptibility and resistivity curves. These transitions are of charge order type. Below the transition temperature the magnetic susceptibility showed low dimensional behavior in both compounds, especially spin gap behavior in Sr_0.33V₂O₅. Such behavior is closely related to the crystal structure characteristic of the vanadium β-bronzes and a manner of ordering for magnetic V⁴⁺ ions at the transition.     

Crystal Structures and Phase Transformations of the Fluorinated Fullerenes

Abstract

In situ x-ray diffraction experiments of the fluorinated fullerenes, C₆₀F _x (x = 0, 36 and 48) at high temperatures have been undertaken. The structural phase transformation of C₆₀F₄₈ was observed at about 358 K. It was also found that the lattice parameters of the low temperature phase of C₆₀F₄₈ show anomalous change at about 310 K. The thermal expansion coefficients of the fluorinated fullerenes were determined by using the change of the lattice parameters with temperature.     

Pressure and Temperature Induced Frequency Shifts of Raman-Active Phonons in the MX Solid Pt2Br6(NH3)4

Abstract

We report the dependencies on hydrostatic pressure up to 100 kbar, and on temperature from 10 K to 300 K of the frequencies of Raman-active stretching modes in the single crystal MX chain solid Pt₂Br₆(NH₃)₄ (PtBrn). The data show that a predicted pressure-induced metallization does not occur, and suggests instead that either a 3-D structural distortion or a transition to a broken-symmetry ground state different from the charge-density wave (CDW) takes place.     

Migration and Annihilation of Triplet Excitation Energy in the Charge-Transfer Anthracene-Tetrachlorophtalic Anhydride Crystal

Abstract

The emission spectra of the charge-transfer crystal of anthracene-tetrachlorophtalic anhydride were studied in the 1.7-300 K temperature range. Delayed fluorescence was observed over the whole temperature range. At temperatures below ～40 K it results from heterogenous (mobile exciton-trapped exciton) triplet-triplet annihilation. At higher temperatures it is due to homogenous triplet-triaplet annihilation. The existence of mobile excitons is also proved by the character of the ESR lines which are very narrow Lorentzians. The phosphorescence, observed only in the range 1.7–40 K, originates from at least two different kinds of traps with energies ～6 cm^?1 and ～140 cm^?1, respectively. The vibrational structure of the phosphorescence is identical to that of anthracene, with 0—0 band blue-shifted by ～400cm^?1. A kinetic model of trapping and detrapping of triplet excitons as well as the nature of the traps are discussed.     

Etude par Calorimetrie,Diffraction des Rayons X et Diffusion Raman d'une Transition de Phase dans (C4 H4P) Mn (CO)3

Abstract

Heat capacity measurements (95-300K), X-ray diffraction (78-300K) and low frequency Raman spectroscopy (10-350K) have evidenced an order-disorder phase transition in phosphacymantrene, (C₄ H₄P) Mn (CO)₃. This transition has been characterized by a monoclinic ←→ triclinic structural change at about 110 K and by a pretransitional phenomenon. The measured transition enthalpy and entropy are 480 ± 10J.mil^?1 and 4.17 ± 0.08J.K^?1 mol^?1, at 115 K, respectively.

A complete assignment of the observed Raman bands in h₄ and d₄ derivatives is proposed. From the temperature dependence of frequencies, intensities and half-widths of some Raman bands we have discussed the order, the nature and the mechanism of the phase transition: intermolecular interactions appear to be mainly involved in the mechanism and an activation energy roughly equal to 2100 ± 840 J. mol^?1 has been determined.     

The Heat Capacity of 1,2,4,5-Tetracyanobenzene and of its 1 : 1 Charge-Transfer Complex with Pyrene from 10 K to 300 K

Abstract

The heat capacity of 1,2,4,5-tetracyanobenzene and of its 1 : 1 complex with pyrene has been measured form ～ 10 K to ～ 300 K. There is a transition in the complex which appears as an approximately symmetrical anomaly in the heat capacity-temperature curve between ～ 220 K and 250 K, but the heat capacity is not reproducible in this region even if the sample is subjected to the same preliminary thermal treatment. Moreover, the room-temperature form can be undercooled at least down to 150 K. In the two runs in which the heat capacity anomaly was most prominent. C_p reached its maximum at 232 ± 1 K. The largest measured value of the entropy of transition was 9.2 JK^?1 mol^?1. This value is compatible with but does not prove, the exisstence of static disorder above the transition, with one of the components (pyrene, in the light of the structural information) having at least two distinguishable orientations. At all temperatures in the range covered (apart from the transition region), the heat capacity of the complex is less than the sum of that of the pure components, and possible reasons for this are brifly discussed.     

Effect of Pressure on Antiferromagnetic Transition in Alkali-Electro-Sodalite

Abstract

Pressure (0–19 kbar) and temperature (4–300 K) dependent EPR study of Sodium-Electro-Sodalite (SES) is presented. SES, which consists of a bcc sub-lattice of F-centers supported by a zeolite-like framework, is known to be a Mott insulator at room temperature. On cooling, SES undergoes an AF transition at 48±2 K providing the first example of an s-electron antiferromagnet. We find that the width of the EPR resonance above T _N is influenced not only by a strong exchange interaction, but also by a fast spin-lattice relaxation. Also, with increasing pressure, T _N decreases linearly and extrapolates to 0 K at about 65 kbar. The reason for this seemingly unexpected behavior is briefly discussed.