Optical charge transfer transitions in supramolecular fullerene and porphyrin compounds

By the DFT method with the planar wave basis set and in the PAW approximation the geometric and electronic structures of four supramolecular compounds of porphyrin and fullerene molecules in the crystalline state are performed: H₂TPP·C₆₀·3 toluene, H₂T_pivPP·C₆₀, H₂T_3,5-dimethylPP·C₇₀·4 toluene, and NiT_4-methylPP·2C₇₀·2 toluene. The geometry is optimized using the PBE functional and the Grimme DFT-D2 dispersion interaction correction. The electronic structure and absorbance spectra are calculated using the HSE functional. It is shown that the H₂TPP·C₆₀·3 toluene structure having a sufficiently wide absorbance wavelength range, which results in a photoinduced electron transition from the higher occupied states formed by porphyrin molecules to the lower unoccupied states formed by fullerene molecules, is most promising for the design of photogalvanic elements.     

Through bond mechanism versus exciplex formation in the photochemistry of fullerene / ferrocene donor-bridge-acceptor dyads

A systematic fluorescence and flash photolytic investigation of a series of covalently linked fullerene / ferrocene based donor-bridge-acceptor dyads is reported as a function of the nature of the bridge between the donor site and acceptor site. The fluorescence of the investigated dyads 2 (Φ_rel = 0.17 × 10^?4, 3 (Φ_rel = 0.78 × 10^?4), 4 (Φ_rel = 1.5 × 10^?4), 5 (Φ_rel = 0.7 × 10^?4), and 6 (Φ_rel = 2.9 × 10^?4) were substantially quenched, relative to N-methyl fulleropyrrolidine (1) (Φ_rel = 6.0 × 10^?4). Photolysis of N-methyl fulleropyrrolidine (1) in toluene revealed formation of the excited singlet state which was followed by a rapid intersystem crossing to the excited triplet state. On the other hand, the fate of the excited singlet state of 2, 3, 4, 5, and 6 was found to be governed by rapid intramolecular quenching, with rate constants of 28×10⁹ s^?1, 6.9×10⁹ s^?1, and 3.4×10⁹ s^?1, 14×10⁹ s^?1, 2.3×10⁹ s^?1 respectively. The electron transfer process and the charge separation were confirmed by monitoring the characteristic π-radical anion bands at λ_max = 400 and 1055 nm in degassed benzonitrile with τ_1/2 = 1.8 μs (3) and 2.5 μs (4).     

Impact of bridging units on the dynamics of photoinduced charge generation and charge recombination in donor-acceptor dyads.

We estimate, at a full quantum-chemical level, the various molecular parameters governing the rate of photoinduced charge generation and charge recombination in model organic structures containing a donor and an acceptor unit in view of the possible use of such systems in organic solar cells. The rate of through-space excitation dissociation, as predicted in the framework of the Marcus-Levich-Jortner theory, is found to be low in comparison to intramolecular decay processes when the donor and acceptor molecules are lying in a head-to-tail arrangement and high when the donor and acceptor molecules are superimposed in a cofacial arrangement. The charge separation rates for side-by-side donor-acceptor dyads are significantly increased by promoting through-bond interactions in covalently linked donor and acceptor units. This has motivated a detailed quantitative analysis of the influence of the nature, size, and conformation of the bridging moiety on the calculated transfer rates.     

Determination of the effective concentration of free charge carriers in solid proton-conducting electrolytes

A method for the theoretical determination of the effective concentration of free charge carriers in solid proton-conducting electrolytes with the use of experimentally measured values of the electrical conductivity has been proposed. Polyantimonic acid has been considered as an example. It has been shown that the high electrical conductivity of solid proton-conducting electrolytes in comparison to other compounds with hydrogen bonds is due to the high concentration of effective free charge carriers and the low activation energy for the mobility of a proton.Translated from Teoreticheskaya i éxperimental'naya Khimiya, Vol. 24, No. 1, pp. 111–114, January–February, 1988.     

Fluorometric determination of heparin based on self-quenching of fluorescein-labeled protamine

A new signaling technique for a fluorometric heparin assay has been developed using the self-quenching of fluoresceinisothiocyanate-labeled protamine (F-protamine). The binding between F-protamine and heparin led to a significant fluorescence quenching due to enhancing the proximity of the F-protamine molecules. The fluorescence of F-protamine (5.9 μg/mL) decreased to 13% in the presence of 2.0 μg/mL heparin. An advantage of this self-quenching system is that the detection can be carried out without using other indicators. With the present system, we could monitor the therapeutic level of heparin in bovine plasma, and the response was quick. These properties of the self-quenching system are suitable for practical use.     

Electronic coupling for charge transfer in donor-bridge-acceptor systems. Performance of the two-state FCD model

Electronic coupling is a key parameter that determines the rate of electron transfer reactions and electrical conductivity of molecular wires. To examine the performance of a two-state approach based on the orthogonal transformation of adiabatic states to diabatic states, we compare the effective donor-acceptor coupling V(DA) computed with three different approaches in model donor-bridge-acceptor (D-B-A) systems. It is found that V(DA) derived with the two-state method accounts properly for both the direct and superexchange interactions. The approach becomes, however, less accurate with the increasing energy difference of the donor and acceptor states. We suggest a simple diagnostic to identify the situation when the estimated coupling might be inaccurate and consider how to improve the performance of the two-state scheme in such a case.     

Identification of a totally charge separated state in completely rigid trichromophoric compounds

Two ‘triads’ 1-syn and 1-anti were investigated containing the same linear arrangement of two electron donors and an acceptor connected by fully rigid saturated hydrocarbon bridges. The systems differ in the relative orientation of the bridges and thereby in the distance between the terminal chromophores which is ≈ 14.9 and ≈ 19.4 Å in the syn and anti isomer respectively. For both systems full charge separation between the terminal chromophores is shown to occur upon photoexcitation of the central donor chromophore, but the lifetime of this charge separation is dramatically longer in 1-anti.     

Photo and thermal reactivity of halogenocyclohexadienones in charge transfer complexes and in the solid state

This article is a brief survey on studies found in the literature on the development of photoreactive and thermal processes of halogenocyclohexadienones in organized media.     

Impact of arginine-modified solid lipid nanoparticles on the membrane charge of human brain-microvascular endothelial cells

Electrokinetic and electrostatic properties of human brain-microvascular endothelial cells (HBMECs) with the uptake of l-arginine (Arg)-modified solid lipid nanoparticles (RSLNs) were investigated. The exposure of these HBMECs to radiofrequency electromagnetic field (EMF) was also considered. As compared with the original culture of HBMECs, the uptake of the biomimetic RSLNs induced smaller absolute values of electrophoretic mobility, zeta potential, Donnan potential, and fixed charge density. In addition, an increase in the coverage fraction of Arg on the external layers of the RSLNs reduced the electrical characteristics of HBMECs. An increase in the power of EMF also decreased the charge of RSLNs-incorporating HBMECs. On the contrary, softness of HBMECs was enhanced by an increased coverage fraction of Arg and an increased power of EMF. Electrophysiology of HBMECs can be efficiently mediated by the novel RSLNs and exposure to EMF through fluctuation and redistribution of the membrane charge.     

The Jahn-Teller effect in solid state chemistry of transition metal compounds

The general features of the local and cooperative Jahn-Teller effect of dⁿ cations with E_g ground states in octahedral coordination and simple model structures are discussed. Examples of different cooperative Jahn-Teller ordering patterns and of phase transitions from static to partially dynamic and finally fully dynamic Jahn-Teller determined structures are given. While in general a tetragonally elongated coordination of the Jahn-Teller ions is favored, the compressed configuration may be stabilized under certain conditions also. It is demonstrated by some examples that the extent of the Jahn-Teller distortion depends on the symmetry and connection pattern of the polyhedra in the host lattice structure. Finally it is shown that the crossover between high- and low-spin configurations of d⁷ cations is strongly influenced by the additional Jahn-Teller stabilization of the low-spin ²E_g state.     

Conformational and photophysical studies on porphyrin-containing donor-bridge-acceptor compounds. Charge separation in micellar nanoreactors

Photophysical studies with semi-rigid, 1, and flexible, 2, donor-bridge-acceptor (D-b-A2+) molecules with D a porphyrin and A2+ a methyl viologen moiety, were performed in neat polar solvents as well as included in surfactant (DTAB) aqueous and in reverse AOT/n-alkane micelles. The micelles acted as nanoreactors for the photoinduced electron transfer reaction upon laser excitation. In spite of the longer lifetime of the charge separated (CS) state in the semi-rigid tetrad 1(ca. 200 ns vs. ca. 100 ns for the flexible dyad 2), the CS formation quantum yield, for example in acetonitrile, was lower for the former (phi(CS) = 0.13) than for the latter (0.58). Comparison of the time-resolved fluorescence data in neat solvent and in the micelles yielded the phi(CS) values in the dilute micellar solutions. Application of laser-induced optoacoustic spectroscopy at various temperatures to 1 dissolved in a polar organic solvent (benzonitrile, BZN) included in aqueous DTAB nanoreactors afforded structural volume changes for the production in hundreds of ps of the CS state upon excitation of a polar molecule. The contraction during CS formation upon excitation of the collapsed conformer in BZN is attributed to the entering of solvent into the open molecular cavity. The opening upon formation of the CS state due to photoinduced electron transfer in the 1 collapsed conformation arises from the repulsion of the two positively charged ends in this state, as previously calculated. Inclusion of 1 in reverse AOT micelles in various n-alkanes also led to a contraction upon excitation, but the data had much more error due to the limited range of variability of the ratio of thermoelastic parameters. The data obtained with the more flexible "supermolecule" 2 showed the predicted large conformation flexibility of these molecules.     

Role of bridge energetics on the preference for hole or electron transfer leading to charge recombination in donor-bridge-acceptor molecules

The impact of donor-acceptor electronic coupling and bridge energetics on the preference for hole or electron transfer leading to charge recombination in a series of donor-bridge-acceptor (D-B-A) molecules was examined. In these systems, the donor is 3,5-dimethyl-4-(9-anthracenyl)-julolidine (DMJ-An) and acceptor is naphthalene-1,8:4,5-bis(dicarboximide) (NI), while the bridges are either oligo(p-phenyleneethynylene) (PE(n)P, where n = 1-3) 1-3 or oligo(2,7-fluorenone) (FN(n), where n = 1-3) 4-6. Photoexcitation of 1-3 and 4-6 produces DMJ(+?)-An-PE(n)P-NI(-?) and DMJ(+?)-An-FN(n)-NI(-?), respectively, which undergo radical pair intersystem crossing followed by charge recombination to yield both (3*)An and (3*)NI, which are observed by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. (3*)NI is produced by hole transfer from DMJ(+?) to NI(-?), while (3*)An is produced by electron transfer from NI(-?) to DMJ(+?), using the agency of the bridge HOMOs and LUMOs, respectively. By monitoring the initial population of (3*)NI and (3*)An in 1-6, the data show that charge recombination occurs preferentially by selective hole transfer when the bridge is PE(n)P, while it occurs by preferential electron transfer when the bridge is FN(n). Over time, the initial population of (3*)NI decreases, while that of (3*)An increases, indicating that triplet-triplet energy transfer (TEnT) occurs. The observed distance dependence of TEnT from (3*)NI to An is weakly exponential with a decay parameter β = 0.08 ?(-1) for the PE(n)P series and β = 0.03 ?(-1) for the FN(n) series. In the PE(n)P series, this weak distance dependence is attributed to a transition from the superexchange regime to hopping transport as the energy gap for triplet energy injection onto the bridge becomes significantly smaller as n increases, while in the FN(n) series the corresponding energy gap is small for all n resulting in triplet energy transport by the hopping mechanism.     

Phase equilibria in the solid state in the U-Mo-UC concentration range of the U-Mo-C system

Part of the phase diagram of the ternary U-Mo-C system was constructed from the topologically different isothermal sections in the temperature range 1100-550°C which were derived from the U-Mo and U-C phase diagrams and from the experimental isothermal section of the U-Mo-C system at 900°C reported by Ruby and Benesovsky. This theoretical phase diagram is compared with experimental data reported by Streets and Stobo and it is found that these workers interpreted their experimental results incorrectly.     

Solid state reactivity of organic compounds with inorganic compounds. IV synthesis and thermal decomposition of uranium oxinate in the solid state

8-hydroxyquinoline (oxine) and uranyl acetate react in the solid state in 13 stoichiometry to give UO₂(C₉H₆NO)₂·C₉H₆NOH. This reaction is diffusion controlled with an activation energy of 44.4 kJ mol^–1. The reaction occurs by the surface migration of 8-hydroxyquinoline, which penetrates the product lattice to react with uranyl acetate. The isothermal decomposition of the solution phase product UO₂Q₂·HQ (Q=C₉H₆NO) obeys the Prout-Tompkins equation with an energy of activation of 53.3 kJ mol^–1.

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Zusammenfassung Die Festkörperreaktion von 8-Hydroxychinolin und Uranylazetat im Verhältnis 13 liefert UO₂(G₉H₆NO)₂·C₉H₆NOH. Die Reaktion ist diffusionsbestimmt und besitzt eine Aktivierungsenergie von 44.4 kJmol^–1. Die Reaktion verläuft durch die Oberflächenmigration von 8-Hydroxychinolin, welches zur Reaktion mit Uranylazetat in das Gitter des Produktes eindringt. Die thermische Zersetzung der Mischphase UO₂Q₂·HQ mitQ=C₉H₆NO unterliegt der Prout-Tompkins-Gleichung mit einer Aktivierungsenergie von 53,3 kJ·mol^–1.

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8- 13, UO₂(C₉H₆NO)₂·C₉H₆NOH. 44,4 ·^–1. 8-, . UO₂ Q ₂ · HQ (Q=C₉H₆NO) - 53,3 ·^–1.

     

The effect of fullerene derivative on polaronic charge transfer in poly(3-hexylthiophene)/fullerene compound

The effect of a structure of a fullerene derivative on electronic properties of poly(3-hexylthiophene)/fullerene composite was studied at 3 cm wave band EPR in wide (77-320 K) temperature region. All the systems with different fullerene derivatives demonstrate sum spectrum of small polarons with different mobilities and contributions depending on the structure of the fullerene derivative. Both the spin-lattice and spin-spin relaxation times were determined separately by using the steady-state saturation method. The treatment of polymer matrix by fullerene derivative changes its dimensionality and conformation. This leads to the change in the spin relaxation and susceptibility as well as in the rate of polaron diffusion along polymer chain.     

Thermal and spectroscopic study of the lanthanide 2-aminoterephthalate compounds in the solid state

Lanthanides 2-aminoterephthalate compounds were synthetized and characterized on the basis of TG–DTA data in order to study their thermal behavior, as well as to establish hydration grade and stoichiometry, while TG/FTIR system identified the gaseous products evolved during the thermal decomposition of these compounds in each step of the TG curve, in which water and carbon dioxide were the main products with a small amount of carbon monoxide and ammonia. Through the FT-IR spectroscopic data of the compounds in the solid state, information concerning the coordination mode of the carboxylate groups to the metal was provided, and by analysis of fluorescence, with excitation at 405 nm, the respective electronic transitions supported by the data reported in the literature were identified. In addition, the excitation was made for the ligand salt and acid with the aim of understanding the contribution of the ligand in the emission of the compounds. In summary, the ligand influenced on the fluorescence of lanthanide ions, being more intense for the compounds of La, Ce, Pr, and Nd, making this material interesting for optical and photonic applications.     

Tetraorganylammonium superoxide compounds: close to unperturbed superoxide ions in the solid state

Trimethylphenylammonium superoxide (1) and tetrabutylammonium superoxide (2) were prepared by ion-exchange reaction in liquid ammonia. Both compounds were structurally characterized by single-crystal X-ray diffraction. The crystal structure of 2 contains solvent ammonia molecules that are hydrogen bonded to the superoxide ion and therefore may influence the bonding properties of the superoxide ion. The crystal structure of 1 does not contain any solvent molecules. Therefore, it represents the best known approximation to the virtually isolated superoxide ion in the solid state to date. The O-O bond length is 1.332(2) A in 1 and 1.312(2) A in 2. Magnetization measurements show that the susceptibilities of both compounds follow an ideal Curie law down to 2 K reflecting an absence of intermolecular exchange effects between the superoxide ions. The effective magnetic moments of both compounds are larger than the spin-only value due to contributions of the orbital momentum in the superoxide ion. The values of the magnetic moment comply well with the g factors obtained from electron paramagnetic resonance spectra. The g tensors themselves reflect the anisotropic environment of the superoxide ions. The Pi(g) energy levels which are degenerate in the free superoxide ion split up in crystal fields of lower than tetragonal symmetry. The energy splitting is estimated from the diagonal elements of the g tensor of 1.     

Solvent free reactions in the solid state: solid state metathesis

Transition Metal Chemistry -     

Real-time PCR in a plastic chip based on solid state FRET

We show a novel solid state optical detection platform, integrated in a plastic biochip, based on colloidal nanocrystal FRET donors. The approach exploits a "smart" polymeric layer with both optical and biorecognition properties that allows real-time monitoring of biomolecular interactions and quantitative analyses of real-time PCR. The proposed strategy, demonstrated here for DNA detection, may open interesting perspectives for a wide range of applications, such as for proteomic studies.