Polarization Caging in Diffusion-Controlled Electron Transfer Reactions in Solution

In some bimolecular diffusion-controlled electron transfer (ET) reactions such as ion recombination (IR), both solvent polarization relaxation and the mutual diffusion of the reacting ion pair may determine the rate and even the yield of the reaction. However, a full treatment with these two reaction coordinates is a challenging task and has been left mostly unsolved. In this work, we address this problem by developing a dynamic theory by combining the ideas from ET reaction literature and barrierless chemical reactions. Two-dimensional coupled Smoluchowski equations are employed to compute the time evolution of joint probability distribution for the reactant (P-(1)(X,R,t)) and the product (p((2))(X,R,t)), where X, as is usual in ET reactions, describes the solvent polarization coordinate and R is the distance between the reacting ion pair. The reaction is described by a reaction line (sink) which is a function of X and R obtained by imposing a condition of equal energy on the initial and final states of a reacting ion pair. The resulting two-dimensional coupled equations of motion have been solved numerically using an alternate direction implicit (ADI) scheme (Peaceman and Rachford, J. Soc. Ind. Appl. Math. 1955, 3, 28). The results reveal interesting interplay between polarization relaxation and translational dynamics. The following new results have been obtained. (i) For solvents with slow longitudinal polarization relaxation, the escape probability decreases drastically as the polarization relaxation time increases. We attribute this to caging by polarization of the surrounding solvent, As expected, for the solvents having fast polarization relaxation, the escape probability is independent of the polarization relaxation time. (ii) In the slow relaxation limit, there is a significant dependence of escape probability and average rate on the initial solvent polarization, again displaying the effects of polarization caging. Escape probability increases, and the average rate decreases on increasing the initial polarization. Again, in the fast polarization relaxation limit, there is no effect of initial polarization on the escape probability and the average rate of IR. (iii) For normal and barrierless regions the dependence of escape probability and the rate of IR on initial polarization is stronger than in the inverted region. (iv) Because of the involvement of dynamics along R coordinate, the asymmetrical parabolic (that is, non-Marcus) energy gap dependence of the rate is observed.

Synthesis, Structure and Optical Studies of a Family of Three-Dimensional Rare-Earth Aminoisophthalates M(mu(2)-OH)(C8H5NO4)] (M = Y3+, La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, and Er3+)

A hydrothermal reaction of the acetate salts of the rare-earths, 5-aminoisophthalic acid (H(2)AIP), and NaOH at 150 degrees C for 3 days gave rise to a new family of three-dimensional rare-earth aminoisophthalates, M(mu(2)-OH)(C8H5NO4)] M = Y3+ (I), La3+ (II), Pr3+ (III), Nd3+ (IV), Sm3+ (V), Eu3+ (VI), Gd3+ (VII), Dy3+ (VIII), and Er3+ (IX)]. The structures contain M-O(H)-M chains connected by AIP anions. The AIP ions are connected to five metal centers and each metal center is connected with five AIP anions giving rise to a unique (5,5) net. To the best of our knowledge, this is the first observation of a (5,5) net in metal-organic frameworks that involve rare-earth elements. The doping of Eu3+/(3+) ions in place of Y3+/ La3+ in the parent structures gave rise to characteristic metal-centered emission (red = Eu3+, green = Tb3+). Life-time studies indicated that the excited emission states in the case of Eu3+ (4 mol-% doped) are in the range 0.287-0.490 ms and for Tb3+ (4 mol-% doped) are in the range of 1.265-1.702 ms. The Nd3+-containing compound exhibits up-conversion behavior based on two-photon absorption when excited using lambda = 580 nm.

Electron paramagnetic resonance studies of some ternary oxides of copper (II)

The electron paramagnetic resonance (EPR) of ternary oxides of Cu(II) has been studied between 4.2 and 300 K. The systems include those with 180 degrees Cu-O-Cu interactions (such as Ln2CuO4, Sr2CuO2Cl2, Sr2CuO3 and Ca2CuO3) or 90 degrees Cu-O-Cu interactions (such as Y2Cu2O5 or BaCuO2) as well as those in which the Cu2+ ions are isolated (such as Y2BaCuO5, La1.8Ba1.2Cu0.9O4.8 and Bi2CuO4). The change in the EPR susceptibility as a function of temperature is compared with that of the DC magnetic susceptibility. Compounds with extended 180 degrees Cu-O-Cu interactions which have a low susceptibility also do not give EPR signals below room temperature. For compounds such as Ca2CuO3 with one-dimensional 180 degrees Cu-O-Cu interactions a weak EPR signal is found the temperature dependence of which is very different from that of the DC susceptibility. For Y2BaCuO5 as well as for La1.8Ba1.2Cu0.9O4.8 the EPR susceptibility as well as its temperature variation are comparable with those of the static susceptibility near room temperature but very different at low temperatures. Bi2CuO4 also shows a similar behaviour. In contrast, for Y2Cu2O5, in which the copper ions have a very distorted nonsquare-planar configuration, the EPR and the static susceptibility show very similar temperature dependences. In general, compounds in which the copper ions have a square-planar geometry give no EPR signal in the ground state (0 K) while those with a distortion from square-planar geometry do give a signal. The results are analysed in the light of recent MS Xalpha calculations on CuO46- square-planar clusters with various Cu-O distances as well as distortions. It is suggested that in square-planar geometry the ground state has an unpaired electron in anionic orbitals which is EPR inactive. Competing interactions from other cations, an increase in Cu-O distance or distortions from square-planar geometry stabilise another state which has considerably more Cu 3d character. These states are EPR active. Both these states, however, are magnetic. For isolated CuO46- clusters the magnetic interactions seem to involve only the states which have mainly anionic character.

Electron field emission from sp (2)-induced insulating to metallic behaviour of amorphous carbon (a-C) films

The influence of concentration and size of sp (2) cluster on the transport properties and electron field emissions of amorphous carbon films have been investigated. The observed insulating to metallic behaviour from reduced activation energy derived from transport measurement and threshold field for electron emission of a-C films can be explained in terms of improvements in the connectivity between sp (2) clusters. The connectivity is resulted by the cluster concentration and size. The concentration and size of sp (2) content cluster is regulated by the coalescence of carbon globules into clusters, which evolves with deposition conditions.

Time-Resolved Resonance Raman Studies on Proton-Induced Electron-Transfer Reaction from Triplet Excited State of 2-Methoxynaphthalene to Decafluorobenzophenone

In this paper time-resolved resonance Raman (TR3) spectra of intermediates generated by proton induced electron-transfer reaction between triplet 2-methoxynaphthalene ((ROMe)-R-3) and decafluorobenzophenone (DFBP) are presented The TR3 vibrational spectra and structure of 2-methoxynaphthalene cation radical (ROMe+) have been analyzed by density functional theory (DFT) calculation It is observed that the structure of naphthalene ring of ROMe+ deviates from the structure of cation radical of naphthalene

Infrared divergences and confinement in massive (2+1)-dimensional QED

In (2+1)-dimensional quantum electrodynamics with massless photons and massive matter fields, it is shown that the mass renormalization of the latter is infrared divergent at one loop. This result remains unchanged at two loops. A simple argument based on a similar divergence of the Coulomb potential leads us to conjecture that charged states are not observable in this model. This argument holds in 1+1 dimensions also.

Covalent attachment of two important dicopper(II) systems in a one-dimensional polymeric chain: An x-ray structure of [Cu2(en)2(OH)2·Cu2(O2CMe)4](PF6)2·0.5EtOH]α showing the shortest Cucdots, three dots, centeredCu Distance in the tetraacetato core

Reaction of Cu2(O2CMe)4(H2O)2 with 1,2-diaminoethane(en) in ethanol, followed by the addition of NH4PF6, led to the formation of a covalently linked 1D polymeric copper(II) title complex showing alternating [Cu2(en)2(OH)22+] and [Cu2(O2CMe)4] units in the chain and the shortest Cucdots, three dots, centeredCu separation of 2.558(2) Å in the tetraacetato core.

The Zintl ion As-7](2-): an example of an electron-deficient As-x radical anion

K(2,2,2-crypt)](2)As-7]center dot THF, 1 (2,2,2-crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo8.8.8]hexacosane) is the first well characterized seven-atom radical anion of group 15. UV-Vis spectroscopy confirms the presence and electronic structure of As-7](2-). Cyclic voltammetry in DMF solution shows the As-7(3) /As-7(2) redox couple as a one-electron reversible process. Theoretical investigations explore the bonding and properties of compound 1.

Electron donor-acceptor complexes of I-2 with diethyl ether and diethyl sulphide. An ab initio MO study

The charge-transfer complexes of I-2 with the n-donors diethyl ether and diethyl sulfide were studied at the Hartree-Fock and MP2 levels. The structures were fully optimized using the 3-21G((*)) basis set as well as with effective core potentials. The calculations consistently yield a C-2v structure for the ether-I-2 complex, but an unsymmetrical form for the sulfide-I-2 complex. A natural bond orbital analysis and the BSSE-corrected complexation energies reveal stronger interactions in the sulfide complex. The computed orbital energies of the monomers and complexes reproduce the trends in experimentally observed vertical ionization potentials.

Spin state and exchange in the quasi-one-dimensional antiferromagnet KFeS2

We report the optical spectra and single crystal magnetic susceptibility of the one-dimensional antiferromagnet KFeS2. Measurements have been carried out to ascertain the spin state of Fe3+ and the nature of the magnetic interactions in this compound. The optical spectra and magnetic susceptibility could be consistently interpreted using a S = 1/2 spin ground state for the Fe3+ ion. The features in the optical spectra have been assigned to transitions within the d-electron manifold of the Fe3+ ion, and analysed in the strong field limit of the ligand field theory. The high temperature isotropic magnetic susceptibility is typical of a low-dimensional system and exhibits a broad maximum at similar to 565 K. The susceptibility shows a well defined transition to a three dimensionally ordered antiferromagnetic state at T-N = 250 K. The intra and interchain exchange constants, J and J', have been evaluated from the experimental susceptibilities using the relationship between these quantities, and chi(max), T-max, and T-N for a spin 1/2 one-dimensional chain. The values are J = -440.71 K, and J' = 53.94 K. Using these values of J and J', the susceptibility of a spin 1/2 Heisenberg chain was calculated. A non-interacting spin wave model was used below T-N. The susceptibility in the paramagnetic region was calculated from the theoretical curves for an infinite S = 1/2 chain. The calculated susceptibility compares well with the experimental data of KFeS2. Further support for a one-dimensional spin 1/2 model comes from the fact that the calculated perpendicular susceptibility at 0K (2.75 x 10(-4) emu/mol) evaluated considering the zero point reduction in magnetization from spin wave theory is close to the projected value (2.7 x 10(-4) emu/mol) obtained from the experimental data.

A Layered Zinc Phosphate, [C6N4H22][Zn6(PO4)4(HPO4)2], Formed by One-Dimensional Tubes

An open-framework zinc phosphate, [C6N4H22][Zn6(PO4)4(HPO4)2] (I), with alternating inorganic and organic layers has been synthesized hydrothermally from a starting mixture of ZnO, HCl, H3PO4, H2C2O4, and triethylenetetramine. Single-crystal data for I: monoclinic, space GROUP =P21/c (No. 14), a=9.881(1), b=16.857(1), c=8.286(1) Å, β=96.7(1)°, V=1370.8(1) Å3, Z=2, R1=0.06, and wR2=0.13 [1408 observed reflections with I>2σ(I)]. The structure of I comprises a network of ZnO4, PO4, and PO3(OH) tetrahedra forming one-dimensional tubes. The tubes, in turn, are linked via oxygen atoms forming macroanionic inorganic layers with eight-membered apertures. The one-dimensional tube-like architecture in I is a novel feature worthy of note.

Symmetry of one-dimensional dynamical systems in terms of transfer matrix parameters

The concept of symmetry for passive, one-dimensional dynamical systems is well understood in terms of the impedance matrix, or alternatively, the mobility matrix. In the past two decades, however, it has been established that the transfer matrix method is ideally suited for the analysis and synthesis of such systems. In this paper an investigatiob is described of what symmetry means in terms of the transfer matrix parameters of an passive element or a set of elements. One-dimensional flexural systems with 4 × 4 transfer matrices as well as acoustical and mechanical systems characterized by 2 × 2 transfer matrices are considered. It is shown that the transfer matrix of a symmetrical system, defined with respect to symmetrically oriented state variables, is involutory, and that a physically symmetrical system may not necessarily be functionally or dynamically symmetrical.

Coordination-driven self-assembly of 2D-metallamacrocycles using a shape-selective Pt(2)(II)-organometallic 90 degrees acceptor: design, synthesis and sensing study

Synthesis of a series of two-dimensional metallamacrocycles via coordination-driven self-assembly of a shape-selective Pt(2)(II)-molecular building unit incorporating carbazole-ethynyl functionality is described. An equimolar (1 : 1) combination of a Pt(2)(II)-organometallic 90 degrees acceptor, 1, with rigid linear ditopic donors (L(a) and L(b)) afforded [4 + 4] self-assembled octanuclear molecular squares, 2 and 3, in quantitative yields, respectively [L(a) = 4,4'-bipyridine; L(b) = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar treatment of 1 with an amide-based unsymmetrical flexible ditopic donor, L(c), resulted in the formation of a [2 + 2] self-sorted molecular rhomboid (4a) as a single product [L(c) = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboid, triangle and square) due to the different connectivity of L(c), the formation of a single and symmetrical molecular rhomboid (4a) as the only product is an interesting observation. All the self-assembled macrocycles (2, 3 and 4a) were fully characterized by multinuclear NMR ((1)H and (31)P) and ESI-MS analysis. Further structural insights about the size and shape of the macrocycles were obtained through energy minimization using density functional theory (DFT) calculations. Decoration of the starting carbazole building unit with Pt-ethynyl functionality enriches the assemblies to be more p-electron rich and luminescent in nature. Macrocycles 2 and 3 could sense the presence of electron deficient nitroaromatics in solution by quenching of the initial intensity upon gradual addition of picric acid (PA). They exhibited the largest quenching response with high selectivity for nitroaromatics compared to several other electron deficient aromatics tested.

High room-temperature hole mobility in Ge0.7Si0.3/Ge/Ge0.7Si0.3 modulation-doped heterostructures

Modulation-doped two-dimensional hole gas structures consisting of a strained germanium channel on relaxed Ge0.7Si0.3 buffer layers were grown by molecular-beam epitaxy. Sample processing was optimized to substantially reduce the contribution from the parasitic conducting layers. Very high hall mobilities of 1700 cm2/V s for holes were observed at 295 K which are the highest reported to date for any kind of p-type silicon-based heterostructures. Hall measurements were carried out from 13 to 300 K to determine the temperature dependence of the mobility and carrier concentration. The carrier concentration at room temperature was 7.9×1011 cm−2 and decreased by only 26% at 13 K, indicating very little parallel conduction. The high-temperature mobility obeys a T−α behavior with α∼2, which can be attributed to intraband optical phonon scattering.

Diketopyrrolopyrrole-Diketopyrrolopyrrole-Based Conjugated Copolymer for High-Mobility Organic Field-Effect Transistors

In this communication, we report the synthesis of a novel diketopyrrolopyrrole-diketopyrrolopyrrole (DPP-DPP)-based conjugated copolymer and its application in high-mobility organic field-effect transistors. Copolymerization of DPP with DPP yields a copolymer with exceptional properties such as extended absorption characteristics (up to similar to 1100 nm) and field-effect electron mobility values of >1 cm(2) V-1 s(-1). The synthesis of this novel DPP-DPP copolymer in combination with the demonstration of transistors with extremely high electron mobility makes this work an important step toward a new family of DPP-DPP copolymers for application in the general area of organic optoelectronics.