Charge Transfer Type Interactions Research Articles

Metal-ligand transport and optical properties of metal sulfide heterostructure: A density functional theory study

The use of metal sulfides for organic photovoltaics has been a widely studied topic in recent years. The current study reports on the impact of aniline and piperidine ligands on the transport and optical properties of SnS/CoS heterostructure, using the first principles density functional theory approach. The charge transfer properties possess an electropositive and electronegative feature for both the aniline and piperidine ligands, respectively. This charge transfer behaviour is consistent with metal-to-ligand charge transfer properties. The optical properties of SnS/ligand/CoS retain its optical plasmonic transitions for both ligand types, with a corresponding damping effect in the absorption, which suggests interfacial charge transfer-type interactions. Also, an increased density of states for both ligand types is observed, implying increased availability of unoccupied states for electronic transport. These results of ligand-incorporated SnS/CoS suggest its potential for future improved charge transfers in organic solar cells.

Excited Charge Separation in a π-Interacting Phenothiazine-Zinc Porphyrin-Fullerene Donor-Acceptor Conjugate.

We have designed, synthesized, and characterized a donor-acceptor triad, SPS-PPY-C60, that consists of a π-interacting phenothiazine-linked porphyrin as a donor and sensitizer and fullerene as an acceptor to seek charge separation upon photoexcitation. The optical absorption spectrum revealed red-shifted Soret and Q-bands of porphyrin due to charge transfer-type interactions involving the two ethynyl bridges carrying electron-rich and electron-poor substituents. The redox properties suggested that the phenothiazine-porphyrin part of the molecule is easier to oxidize and the fullerene part is easier to reduce. DFT calculations supported the redox properties wherein the electron density of the highest molecular orbital (HOMO) was distributed over the donor phenothiazine-porphyrin entity while the lowest unoccupied molecular orbital (LUMO) was distributed over the fullerene acceptor. TD-DFT studies suggested the involvement of both the S2 and S1 states in the charge transfer process. The steady-state emission spectrum, when excited either at porphyrin Soret or visible band absorption maxima, revealed quenched emission both in nonpolar and polar solvents, suggesting the occurrence of excited state events. Finally, femtosecond transient absorption spectral studies were performed to witness the charge separation by utilizing solvents of different polarities. The transient data was further analyzed by GloTarAn by fitting the data with appropriate models to describe photochemical events. From this, the average lifetime of the charge-separated state calculated was found to be 169 ps in benzonitrile, 319 ps in dichlorobenzene, 1.7 ns in toluene for Soret band excitation, and ∼320 ps for Q-band excitation in benzonitrile.

Pyridine-M2+ [M = Mg, Ca]: A promising organometallic system for potential hydrogen storage: In silico study

Pyridine-M2+ [M = Mg, Ca] hosts have been identified as potent H2 storage material, and this has been explored by a variety of functionals within the density functional theory (DFT) context. Around the linearly connected metal centre, the pyridine-Mg2+ and pyridine-Ca2+ building blocks can adsorb 6 and 7H2 molecules, respectively. The stability of Pyridine-M2+ [M = Mg, Ca] hosts has been proven by chemical hardness, aromaticity, and molecular dynamic simulations. After H2 adsorption, the aromaticity still remains. Adsorption of H2 molecules at a quasi-molecular type is supported by the fact that their average adsorption energy/H2 (Eads/H2) is between 0.22 and 0.72 eV. Pyridine-Mg2+@6H2 and pyridine-Ca2+@7H2 both have very impressive gravimetric wt % values (10.43 and 10.53 respectively). Average delocalization correction energy (ΔECTav) supports the charge transfer type interaction between metal ions and adsorbed H2 molecules. The topological analysis reflects that bonding between metals (Mg & Ca) and trapped H2 molecules are mostly non-covalent types. Gibbs free energy changes (ΔG) [eV] indicate that the molecular hydrogen adsorption process will be spontaneous at 298 K for pyridine-Mg2+@nH2 systems and at or below 205 K for pyridine-Ca2+@nH2 systems and atom centered density matrix propagation (ADMP) study suggests the higher temperature for desorption.

Peripheral phenothiazine induced suppression of charge separation from the singlet excited zinc phthalocyanine to coordinated C60 in supramolecular donor–acceptor conjugates

Self-assembled donor–acceptor conjugates featuring zinc phthalocyanine carrying four entities of peripheral phenothiazine entities, (PTZ)[Formula: see text]ZnPc, axially coordinated to either phenyl imidazole or pyridine functionalized fulleropyrrolidine (C[Formula: see text]Im or C[Formula: see text]Py) has been newly designed, synthesized and characterized. Due to the direct connectivity of the phenothiazine entities to the ZnPc [Formula: see text]-system, efficient charge transfer type interactions suppressing fluorescence of ZnPc in (PTZ)[Formula: see text]ZnPc was observed. Axial coordination of C[Formula: see text]Im or C[Formula: see text]Py to the metal center of (PTZ)[Formula: see text]ZnPc served as an electron acceptor in the conjugates. Optical absorption studies revealed stable complex formation wherein the evaluated binding constants [Formula: see text] were found to be 3.9 × 10[Formula: see text] M[Formula: see text] for (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] and 3.3 × 10[Formula: see text] M[Formula: see text] for (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugates with 1:1 molecular stoichiometry. Computational studies performed at the HF/[6-311G(d,p) for H, C, and N, and 6-311G(2df) for S and Zn] level revealed stable structures of the conjugates. The evaluated center-to-center and edge-to-edge distances for the (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] were 13.6 and 10.4 Å, while for the (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugate these distances were 10.2 and 7.3 Å. That is, the C[Formula: see text] was about 3̃ Å closer to ZnPc in the latter conjugate. From the free-energy calculations, photoinduced electron transfer from the [Formula: see text]ZnPc* to fullerene within the conjugates was established to be an exothermic process, however, a hole transfer from ZnPc[Formula: see text] to peripheral PTZ was found to be energetically an uphill process. From femtosecond transient absorbance studies, occurrence of photoinduced charge separation in (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] was found to be weak due to the competing charge transfer interactions within the (PTZ)[Formula: see text]ZnPc and longer donor–acceptor distance while in the case of the (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugate, electron transfer occurred competitively to yield radical ion-pairs. From nanosecond transient spectroscopy, lifetime of the (PTZ)[Formula: see text]ZnPc[Formula: see text]:PyC[Formula: see text] charge separated state was found to be in the 200 ns range, revealing charge stabilization to some extent.

Investigation of the push-pull effects on β-functionalized benzoporphyrins bearing an ethynylphenyl bridge.

A series of β-pyrrole functionalized push-pull porphyrins with amine push groups linked via an ethynylphenyl spacer, and cyclic imide or carboxylic esters as pull groups have been newly synthesized and characterized. The β-pyrrole functionalized ethynylphenyl spacer extends the conjugation of the porphyrin π-system, as reflected by their red-shifted absorbance and fluorescence spectra. The computed structures revealed no steric hindrance between the porphyrin π-system and the β-substituents. The calculated HOMO and LUMO of compounds WJ2 and WJ3 display significant segregation, where the electron density in the HOMO and LUMO is mainly located at the donor component and the acceptor component, respectively. The orbital segregation is likely attributed to the introduction of the electron-donating amine group at the porphyrin periphery. Electrochemical studies revealed the expected lower HOMO-LUMO gap as a result of the facile oxidation and reduction of the push-pull porphyrins. As a consequence of the push-pull effects, a reduction in fluorescence intensity and lifetime was observed, especially for compound WJ3 having two electron-donating amino groups and a strongly electron-withdrawing cyclic imide group. Femtosecond transient absorption spectral studies revealed the successful formation of the singlet excited state in all of these push-pull porphyrins. Due to the occurrence of intramolecular charge transfer-type interactions, relaxation of the singlet excited state was found to be faster in compound WJ3 compared to other two derivatives in polar solvent but not in nonpolar solvent. Such charge transfer-type interactions from the triplet excited state were also observed in the case of compound WJ3 in benzonitrile. The present findings bring out the importance of push-pull effects in governing the ground and excited (singlet and triplet) state properties of free-base porphyrins.

Oligothiophene/graphene supramolecular ensembles managing light induced processes: preparation, characterization, and femtosecond transient absorption studies leading to charge-separation.

Advances in organic synthetic chemistry combined with the exceptional electronic properties of carbon allotropes, particularly graphene, is the basis used to design and fabricate novel electron donor-acceptor ensembles with desired properties for technological applications. Thiophene-based materials, which are mainly thiophene-containing polymers, are known for their notable electronic properties. In this frame moving from polymer to oligomer forms, new fundamental information would help for a better understanding of their electrochemical and photophysical properties. Furthermore, a successful combination of their electronic properties with those of graphene is a challenging goal. In this study, two oligothiophene compounds, which consist of three and nine thiophene-rings and are abbreviated 3T and 9T, respectively, were synthesized and noncovalently associated with liquid phase exfoliated few-layered graphene sheets (abbreviated eG), thus forming donor-acceptor 3T/eG and 9T/eG nanoensembes. Markedly, intra-ensemble electronic interactions between the two components in the ground and excited states were evaluated with the aid of UV-Vis and photoluminescence spectroscopy. Furthermore, redox assays revealed the one-electron oxidation of 3T accompanied by one-electron reduction due to eG in 3T/eG, whereas there were two reversible one-electron oxidations of 9T accompanied by one-electron reduction of eG9T/eG. The electrochemical band gap for the 3T/eG and 9T/eG ensembles were calculated and verified, in which the negative free-energy change for the charge-separated state of 3T/eG and 9T/eGvia the singlet excited state of 3T and 9T, respectively, were thermodynamically favorable. Finally, the results of transient pump-probe spectroscopy studies at the femtosecond time scale were supportive of charge transfer type interactions in the 3T/eG and 9T/eG ensembles. The estimated rates for intra-ensemble charge separation were found to be 9.52 × 10(9) s(-1) and 2.2 × 10(11) s(-1), respectively, for 3T/eG and 9T/eG in THF, which reveal moderate to ultrafast photoinduced events in the oligothiophene/graphene supramolecular ensembles.

The role of interfacial charge transfer-type interactions in the decay of plasmon excitations in metal nanoparticles

This perspective describes the influence of interfacial charge transfer-type interactions on the optical spectra and hot electron cooling processes in plasmonic nanoparticles (NPs), and ongoing work to optimize these interactions for charge extraction from the plasmon or hot electron state. The manuscript focuses on interfaces of metal NPs with organic molecules and with semiconductors. Charge extraction from multi-electron excited states has applications in photodetection, sensing, and conversion of solar energy to electricity and fuels.

Disk Lubricant Additives, A20H and C2: Characteristics and Chemistry in the Disk Environment

Disk lubricant additives A20H and C2 are Fomblin Z type perfluoropolyether with the hydroxyl end-group, –O–CF2–CH2–OH, at one end, and the cyclo-triphosphazene end-group, R5(PN)3–O–, at the other end. Here, R is an m-trifluoromethyl-phenoxy group for A20H and a trifluoroethoxy group for C2. These additives were examined for miscibility with benzene, spin-off rate, water contact angle, and the diffusion rate over the carbon overcoat. It is revealed that A20H adheres to the carbon overcoat spontaneously. The attractive interaction arises from the charge–transfer type interaction between the aromatic rings of the phosphazene end and the graphitic regime of the carbon overcoat. No spontaneous adherence occurs between the lubricant C2 and the carbon overcoat. A TOF-SIMS study of disks coated with A20H and C2, respectively, with and without subsequent curing by short-UV (185 nm) was performed. It is revealed: (1) if presented with a low energy electron, the phenoxy groups of A20H readily undergo the dissociative electron capture, while the trifluoroethoxy group does not, and (2) photoelectrons generated by short-UV have little kinetic energy and the electron capture occurs only if an electrophilic molecular sector is in intimate contact with the carbon. Thus, in the case of disks coated with A20H, UV-curing results in detachment of a phenoxy group in contact with the carbon, generation of a radical center at the phosphorus atom and subsequent formation of a bona fide chemical bond between the phosphor and the carbon overcoat. No reaction of consequence occurs when disks coated with C2 are irradiated with short-UV.

Competitive occurrence of homolytic N–O and heterolytic C–O bond cleavage in excited-state 1-(arylmethyloxy)-2-pyridones

The irradiation at 340 nm of the title compounds having 9-anthryl and pyren-1-yl groups in methanol was found to give the heterolytic C–O bond cleavage products: 1-hydroxy-2-pyridone and aryl-substituted dimethyl ether (which predominate for the reaction of the former title compound) in addition to 2-pyridone, aryl-substituted methanol and aryl-substituted formaldehyde derived from the homolysis of the N–O bond (which mainly occurs in the photolysis of the latter title compound). It was also found that substitution of the methyl group for hydrogen at the 6-position of the pyridone skeleton in 1-(9-anthrylmethyloxy)-2-pyridone decreases the relative composition of the aryl-substituted dimethyl ether to some extent. These substituent effects on the product compositions were explained in terms of stereoelectronic effects on a charge transfer-type interaction between the aromatic and pyridone rings in the singlet excited state. Analyses of the ground-state conformation for the title compounds by MM2 calculations and 1H NMR spectroscopy, as well as of their singlet excited-state behaviour, substantiated the existence of a non-emissive intramolecular exciplex intermediate which plays a key role in inducing the C–O bond heterolysis.

Evidence for metal interaction in gold metallized polycarbonate films: An x-ray photoelectron spectroscopy investigation

The interfacial interactions between in situ thermally evaporated Au and polycarbonate (PC) film, a technologically important polymeric material, is studied by x-ray photoelectron spectroscopy (XPS). Angle resolved XPS is performed to investigate the Au reactivity if any, in forming the metal-polymer interface. The spectral evidence from the above suggests that the metal interacts predominantly with the carbonyl carbon of the monomeric unit with only minor interactions with the phenyl carbons without any complex formation. In contrast to previous findings of Au to be inert at the M-polymer interfaces, this work emphasizes the salient charge transfer type interactions of Au (as electron injector) at the C=O as the primary interaction site, distributing a net charge density to C=O with the formation of a Au-CO π-back bond. The conclusions are supported by the observed new C 1s feature at 282.6 eV and the O 1s and Au 4f7/2 XPS spectral changes. The growth mode of Au on PC was proceeded by the metal monolayer deposition with cluster growth on the already weakly bonded Au onto the C=O carbon of the polymeric backbone.

The stabilization of smectic A phases in mixtures of twinned-calamitic, metal organic complexes with 2,4,7-trinitro-9-fluorenone

The liquid crystal properties of binary mixtures of copper- and palladium-containing, twinnedcalamitic, metal organic complexes with the electron acceptor 2,4,7-trinitro-9-fluorenone (TNF) are reported. The smectic A to isotropic transition temperature of the pure metal organic component is increased on mixing. Furthermore, only smectic A behaviour is exhibited by the mixtures compared with smectic A and C phases for the pure metal organic complexes. The stabilization of the smectic A phase in these mixtures is found to be due to a weak charge transfer type interaction.

Secondary emission from molecule-solid coupled systems with a charge-transfer type interaction

We investigate the secondary optical processes in the three-level system using the Fano-Anderson model. The time-resolved emission spectra are calculated, and we find that lattice relaxation, nonradiative transitions, and interference effects in the excited states bring about the distinctive features in the emission spectra.

電子移動を経由するフリルの光環元反応におよぼす溶媒効果

Furil underwent an efficient photoreduction to selectively afford furoin in benzene and acetonitrile containing triethylamine. A thermodynamic analysis of the reaction suggests the operation of an electrontransfer mechanism. Small steric effects of tertiary amines used on the quantum yields for the formation of furoin was explained in terms of a loose radical ion pair formed by an electron transfer from the ground-state amine to the excited singlet-state furil. A pronounced charge transfer-type interaction between the amine radical cation and benzene molecules in the solvent cage was proposed to interpret a high reactivity of furil in the nonpolar solvent, benzene.

Electrical properties of bilayer lipid membranes containing iodine and iodide, investigated by cyclic voltammetry

The conduction properties of lecithin bilayer membranes in iodine-containing solutions are examined from a potentiodynamic experimental approach. Voltammetric data obtained by using a variety of forms (derived from charge-transfer type interactions) of iodide implicate the triiodide ion as the charge carrier accounting for the diffusion-limited voltammetric response whereas the charge transport of iodide seems to be limited by transmembrane diffusion. The data are used to support one of the many proposed mechanisms for conductance of iodide in membranes.

Spectrophotometric studies on accelerated hydrolysis of iodine in the presence of polyvinylpyrrolidone.

The spectra of iodine in the presence of iodide, iodic acid, and polyvinylpyrrolidone (PVP) were obtained. Large effects of PVP concentrations on the spectra were observed. Changes in iodine spectra in the presence of N-methyl-2-pyrrolidone and N, N-diethyl-propionamide in various solvents indicated charge-transfer type interaction in less polar solvents. The spectra of the aqueous iodine solution were more affected by the addition of PVP with a smaller degree of polymerization. Kinetic studies of hydrolysis of iodine in the absence and presence of PVP indicated that PVP accelerates hydrolysis of iodine except for the initial period. The possible mechanism of accelerated hydrolysis of iodine in the presence of PVP is complexation of triiodide ion with PVP and subsequent shifts in the hydrolysis equilibrium of iodine.

Calculation of intermolecular interactions within the PCILO framework using fixed wave‐functions

AbstractThe PCILO method was used to calculate intermolecular interactions using fixed polarities. In this way our calculations are without any iteration cycle.The investigated supermolecules involve London–van der Waals type, hydrogen bonding type, and charge transfer type interactions, respectively. Both stabilization energies and equilibrium distances are in good agreement with the calculated values using optimized wavefunctions.Also the analysis of the individual contributions to the energy reflects well the mechanism of the intermolecular interactions.

Calculation of intermolecular interactions within the PCILO framework

AbstractThe PCILO method was used to calculate the intermolecular interaction of London–van der Waals type, hydrogen bonding type, and charge transfer type interactions, respectively. The stabilization energies of the calculated supermolecules are: 0.85 kcal · mole−1 for the nonane dimer, 4.15 kcal · mole−1 for the water dimer, and 3.60 kcal · mole−1 for the butene‐2‐cis‐Li+ complex. The analysis of the individual contributions of the energy reflects well the mechanism of the intermolecular interaction.

Anion complexes of Cu(II) bovine carbonic anhydrase

1. The stability constants of some anion complexes of bovine Cu(II) carbonic anhydrase have been determined. They are found to be three-four orders of magnitude higher than those of the corresponding complexes of bovine superoxide dismutase, aqueous copper, and copper compounds of low molecular weight. Stabilization can be achieved either through the additional formation of a hydrogen bond between the anion and the protein in some cases or through donor-acceptor or charge-transfer type interactions in halide complexes. 2. Room temperature experiments show that the EPR spectrum of the cyanide complex is unaffected by pH, so that the change observed by Taylor and Coleman (1) must be produced by freezing. 3. The properties-of halide complexes of Cu(II), Co(II), and Zn(II) carbonic anhydrases are discussed and it is proposed that they give rise to pentacoordinate metal species. This may explain previous NMR data (2) without excluding water as a metal ligand at low pH. 4. The p K a = 8.0 and the HCO 3 − binding constant ( K HCO 3 = 3.5 × 10 3) for Cu(II)BCA are discussed in relation to the lack of activity of Cu(II) carbonic anhydrases.

Ein purin nucleosid in ungewöhnlicher konformation: Kristall- und molekülstruktur von 5′-methylammonium--5′-deoxyadenosin-jodid-monohydrat

5′-Methylammonium-5′-deoxyadenosine is a poor subsrate for adenosine desaminase. The nucleoside was crystallized from aqueous methanol as its iodide monohydrate in space group P2 1. The structure was solved from three dimensional X-ray data and refined to R = 4.1%. The structure of the nucleoside is determined by an intramolecular hydrogen bond from N5′ to N3 which implies that (1) the edenine heterocycle is in syn position with respect to the sugar moiety; (2) the ribose pucker is C2′-exo, C3′-endo and (3) the conformation about the C4′-C5′ bond is trans, gauche. The water of hydration is fourfold disordered and forms a linear hydrophilic region which is surrounded by nucleoside molecules in a zigzag arrangement. The adenine heterocycles are not stacked and in closer than Van der Waals distance with iodine ions suggesting a charge transfer type interaction.

Studies on Photochromic Salicylideneanilines. I. Photo-induced Electron Spin Resonance Spectra in Salicylideneaniline-Phenothiazine Complexes

It has been found that photo-reversible electron spin resonance signals are observed on low-temperature irradiation into various powdered complexes composed of anil and phenothiazine. And on the basis of studies on the photo-stationary structure and photo-after decay rate of the spectrum, a main component of the signal has been proposed as phenothiazine cation which is produced by a charge-transfer type interaction with the photocolored quinoidlike form of anil.