Bias-dependent visualization of electron donor (D) and electron acceptor (A) moieties in a chiral DAD triad molecule

The 2D crystal lattice structure and bias-dependent contrast of a chiral electron donor-acceptor-donor triad system, composed of two oligo(p-phenylene vinylene) electron donors and a perylenediimide electron acceptor (OPV4-PDI-OPV4), have been studied by means of scanning tunneling microscopy (STM) at the liquid-graphite interface. OPV4-PDI-OPV4 is ordered in rows and forms a well-ordered 2D crystal lattice structure. The electrical properties of the donor and acceptor parts are distinguished by the contrast in bias-dependent STM imaging.     

A theoretical study of the inversion barrier in NF3+

The barrier to inversion in NF⁺₃ has been studied using ab initio molecular-orbital theory including geometry optimization at the correlation energy level. The barrier is predicted to be 12.6 kcal mol⁻¹. Comparison is made to previous theoretical and experimental results.     

Fluorescent photoinduced electron transfer (PET) sensing molecules with p-phenylenediamine as electron donor

Fluorescent photoinduced electron-transfer sensors were made from p-phenylenediamine-substituted azacrown ethers attached with a dansyl group, in which the p-phenylenediamine moiety serves as electron donor and the dansyl group acts as the acceptor. Chelation-enhanced fluorescence was observed upon addition of metal salts. Selective fluorescence response was observed for Mg(2+) and/or Ca(2+) versus Na(+) and K(+) due to size match and charge density sensitivity of the p-phenylenediamine moiety.     

Structural, theoretical and multinuclear NMR study of mercury(II) complexes with a new ambidentate phosphorus ylide

The reaction of the new ambidentate ylide, Ph₃PCHCOCH₂COOC₂H₅ (EAPPY), with HgX₂ (X = Cl, Br and I) in equimolar ratios using methanol as the solvent leads to binuclear complexes of the type [EAPPY·HgX₂]₂ (X = Cl (1), Br (2) and I (3)). Single crystal X-ray analysis reveals the presence of a centrosymmetric dimeric structure containing the ylide and HgX₂ (X = Br or I)_. The IR and NMR data of the product [(EAPPY)·HgCl₂]₂ (1), formed by the reaction of mercury(II) chloride with the same ylide, are similar to those of 2 and 3. Analytical data indicate a 1:1 stoichiometry between the ylide and Hg(II) halide in each of the three products. Theoretical studies indicate that the nature of the R group in ylides of the type Ph₃PCHCOR has a weak effect on the Hg-C(ylide) bond length in binuclear Hg₂L₂I₄ complexes.     

N2O4 complexes with electron donor molecules. An STO-3G study

The quantum chemical calculations for N₂O₄ complexes with some electron-donor molecules: CH₃NO₂, CH₃COOH, CH₃CN, C₆H₆ and with another molecule of N₂O₄ show that the donor molecule lies under the N₂O₄ plane and its electron-donor atom points to the center of N-N bond of N₂O₄ (or near this center). The electron charge is transferred from the donor to N₂O₄ molecule, mostly to the N-N bond of N₂O₄.     

Incorporation of cationic electron donor of Ni-pyridyltetrathiafulvalene with anionic electron acceptor of polyoxometalate

A new salt-[Ni(II)(DMSO)(5)(TTFPy)](2)[α-SiW(12)O(40)] (1)-based on polyoxometalates was prepared by coordinating a cationic electron donor of pyridyltetrathiafulvalene (TTFPy) with Ni(II). Although the TTFPy molecule did not form a salt with the anionic α-[SiW(VI)(12)O(40)](4-) because of the weak charge-transfer (CT) interaction, the coordination of Ni with the pyridyl moiety permitted salt formation driven by electrostatic interaction, giving a single crystal of 1. Crystallographic analysis, UV-vis and IR spectroscopy and electrochemical characterization revealed that the fully oxidized α-[SiW(VI)(12)O(40)](4-) was crystallized with the neutral TTFPy moiety from the acetonitrile solution because of the low electron-withdrawing ability of α-[SiW(VI)(12)O(40)](4-), forming a brown-orange crystal. The crystal colour quickly turned to black by immersing in methanol, due to CT from TTF moiety to α-[SiW(VI)(12)O(40)](4-), which was caused by the solvent effect. Increase in the solvent acceptor number from 18.9 for acetonitrile to 41.3 for methanol resulted in the enhancement of the electron withdrawing ability of α-[SiW(VI)(12)O(40)](4-) by 0.317 V in methanol.     

Specific solvent effects on the intramolecular electron transfer reaction in a neutral ferrocene donor polychlorotriphenylmethyl acceptor radical with extended conjugation

The synthesis and the optical, magnetic and electrochemical properties of the ferrocenylbutynene substituted polychlorotriphenylmethyl radical 1 are reported. Radical 1 is prepared in a three step synthetic route starting with a Wittig reaction to yield (E,Z)-{4-[4-(bis(2,3,4,5,6-pentachlorophenyl)methyl)-2,3,5,6-tetra-chlorophenyl]but-3-en-1-ynyl}-ferrocene (1H) which is subsequently deprotonated to yield the corresponding anion K⁺(18-crown-6) [1]^? and finally oxidized to (E)-4-[4-(ferrocenyl)but-3-yn-1-enyl]-2,3,5,6-tetrachlorophenyl-bis(2,3,4,5,6-pentachlorophenyl) methyl radical (1). Radical 1 exhibits a charge-transfer band transition in the near infrared region which is associated with an intramolecular electron transfer from the ferrocene unit (donor) to the radical unit (acceptor) of this dyad molecule; its solvatochromism is studied in detail. The X-ray crystal structure of [K⁺(18-crown-6)](E)-[4-[4-(ferrocenyl)but-3-yn-1-enyl]-2,3,5,6-tetrachlorophenyl-bis(2,3,4,5,6-pentachlorophenyl) methide] [1]^? has been determined. This organic salt forms an interesting one-dimensional coordination polymer by the coordination of the K⁺ cation with chlorine atoms of the organic carbanion.     

Evidence of electron acceptor - electron donor interactions in thermoplastic polymer blends by using FTIR - ATR spectroscopy

Specific interactions in binary blends of ethylene/vinyl acetate copolymer (EVA) with various low molecular weight terpene-phenol tackifying resins (TPR) were systematically investigated, as a function of the composition of the blend and of the electron-acceptor ability of the resin, by using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. Molecular acid-base were evidenced between TPR hydroxyl groups and EVA carbonyl groups. Quantitative information on the fraction of acid-base bonded entities, the enthalpy and the equilibrium constant of pair formation were obtained. A crystalline transition of the EVA copolymer is observed and is discussed in terms of enthalpy and entropy considerations based on FTIR and calorimetric differential scanning calorimetry (DSC) investigations. Fundamental results are then summarized in order to predict the interfacial reactivity of such polymer blends towards acid or basic substrates.     

The theoretical design of neutral planar tetracoordinate carbon molecules with C(C)(4) substructures

Using a new charge-compensation strategy, we designed neutral molecules with perfectly planar C(C)(4)-type tetracoordinate carbon arrangements (ptC) employing DFT computations. These designs, based on the planar preference of methane dications, replace two remote carbons in spiroalkaplanes by borons or two remote hydrogens by BH(3) groups; the two formally anionic boron units which result compensate the formal double positive charge on the central ptC's. The LUMOs correspond to the "wasted" lone pair HOMOs of the alkaplanes. As compared to the latter, pi occupancies on the central carbon are much smaller (less than 0.7e), and the IPs are much larger. The newly predicted compounds utilize all of the electrons more effectively. There are no lone pairs, and the ptC-C bond lengths are ca. 1.50 A. The Wiberg bond index sums of the ptC's are near 3.2, and the boron sums are close to 4.     

Hydrogen bonding patterns in the cocrystals of 5-nitrouracil with several donor and acceptor molecules

: Cocrystals of 5-nitrouracil with solvent molecules, dioxane, pyridine, DMSO, formamide and ethanol as well as with piperazine, N, N'-dimethylpiperazine, 3-aminopyridine and diazabicyclo [2.2.2]octane obtained by deliberate inclusion, have been examined by X-ray crystallography. The tape structure found in the parent centric form of nitrouracil is retained with some modifications in the cocrystals with dioxane, piperazine, diazabicyclo [2.2.2]octane, N,N'-dimethylpiperazine, pyridine and DMSO, with the guest molecules forming alternate tapes. In cocrystals involving formamide, ethanol and 3-aminopyridine, the molecular tapes exhibit mixed compositions. The observed bonding patterns have been classified into six schemes. Interestingly, quadruple type hydrogen bonding patterns are seen in cocrystals containing 3-aminopyridine or ethanol and water, while a network of acyclic tetrahedral pentamers of water is found in the cocrystal containing diazabicyclo [2.2.2]octane and water.     

A Study of Intramolecular Energy Transfer in Conformationally Rigid molecules with stereoisomerically oriented donor and acceptor groups

The indanono naphthaleno compounds 1 , 3 , 5 and 7 exhibit, on both irradiation in the ¹L_b band (315 nm) and the n → π* transition (> 340 nm) in EPA at 77° K, neither fluorescence from naphthalene nor phosphorescence from indanone, but exclusively phosphorescence from naphthalene, and quenching in liquid solution with 1,3-pentadiene results in triplet energy transfer from the naphthaleno group only. The naphthalene phosphorescence exhibited by the ketones ( 1 , 3 , 5 , 7 ) has an enhanced quantum efficiency with respect to that on direct excitation of the corresponding hydrocarbons ( 2 , 4 , 6 , 8 ) and more strongly in the exo than in the endo orientation. In order to account for the energy wasting in the intramolecular triplet energy transfer in the endo compounds, a transfer route via a weak triplet donor-acceptor exciplex, specific to through-space interaction in the endo configuration (providing for additional radiationless T → S energy dissipation through vibrational coupling), competing with an efficient through-σ-bond exchange transfer mechanism operative in both configurations is proposed.     

A theoretical investigation of the interactions between water molecules and ionic liquids

Quantum chemical calculations have been used to investigate the interaction between water molecules and ionic liquids based on the imidazolium cation with the anions [Cl(-)], [Br(-)], [BF(4)(-)], and [PF(6)(-)]. The predicted geometries and interaction energies implied that the water molecules interact with the Cl(-), Br(-), and BF(4)(-0 anions to form X(-)...W (X = Cl or Br, W = H(2)O), 2X-...2W, BF(4)(-)...W, and W...BF(4)(-)...W complexes. The hydrophobic PF(6)(-) anion could not form a stable complex with the water molecules at the density functional theory (DFT) level. Further studies indicate that the cation could also form a strong interaction with the water molecules. The 1-ethyl-3-methylimidazolium cation (Emim(+)) has been used as a model cation to investigate the interaction between a water molecule and a cation. In addition, the interaction between the ion pairs and the water was studied by using 1-ethyl-3-methylimidazolium chloride (Emim x Cl) as a model ionic liquid. The strengths of the interactions in these categories follow the trend anion-W > cation-W > ion pair-W.     

A theoretical study of the reaction of O(3P) with isobutene

The reaction of O((3)P) with isobutene ((CH(3))(2)C=CH(2)) is investigated using the unrestricted second-order M?ller-Plesset perturbation (UMP2) and complete basis set CBS-4M level methods. The minimum energy crossing point (MECP) between the singlet and triplet potential energy surfaces is located using the Newton-Lagrange method, and it is shown that the MECP plays a key role. The calculational results indicate that the site selectivity of the addition of O((3)P) to either carbon atom of the double bond of isobutene is weak, and the major product channels are CH(2)C(O)CH(3) + CH(3,) cis-/trans-CH(3)CHCHO + CH(3), (CH(3))(2)CCO + H(2), and CH(3)C(CH(2))(2) + OH, among which (CH(3))(2)CCO + H(2) is predicted to be the energetically most favorable one. The complex multichannel reaction mechanisms are revealed, and the observations in several recent experiments could be rationalized on the basis of the present calculations. The formation mechanisms of butenols are also discussed.     

A quantum chemical study of trimethoxyaluminum complexes with neutral molecules

The spatial and electronic structures of trimethoxyaluminum complexes with neutral molecules are calculated by the MP2/6-31(2d,p) method using the PC GAMESS-Firefly program package. The main characteristics of aluminum bonds in these molecules are determined by AIM and NBO methods. It is shown that these bonds can be characterized as the bonds between the atoms with closed shells.     

Photochemical reaction of gadolinium(III) tetraphenylporphyrin in toluene solution containing an electron acceptor or donor

In this paper we have studied by absorption spectroscopy the course of the steady state photolysis of gadolinium(III) complex with 5,10,15,20-tetraphenylporphyrin. The result has been compared with the photolysis of free base tetraphenylporphyrin. Irradiation of GdTPP(acac) and H₂TPP (H₂TPP ≡ tetraphenylporphyrin; Hacac ≡ acetylacetone) with visible light in the presence of triethylamine as an electron donor, leads to their photoreduction. Formation of the gadolinium tetraphenylchlorin complex and tetraphenylchlorin is observed. The process of irradiation in the presence of CCI₄ as an electron acceptor has different pathways for GdTPP(acac) and H₂TPP. The gadolinium complex is mono oxidized, giving rise to the π⁺ radical cation while, for unmetallated porphyrin, dication H₄(TPP)²⁺ formation is observed.     

A novel type of donor–acceptor cyclopropane with fluorine as the donor: (3 + 2)-cycloadditions with carbonyls

gem-Difluorocyclopropane diester is disclosed as a new type of donor–acceptor cyclopropane, which smoothly participates in (3 + 2)-cycloadditions with various aldehydes and ketones. This work represents the first application of gem-difluorine substituents as an unconventional donor group for activating cyclopropane substrates in catalytic cycloaddition reactions. With this method, a wide variety of densely functionalized gem-difluorotetrahydrofuran skeletons, which are otherwise difficult to prepare, could be readily assembled in high yields under mild reaction conditions. Computational studies show that the cleavage of the C–C bond between the difluorine and diester moieties occurs upon a S_N2-type attack of the carbonyl oxygen.

A new type of donor–acceptor cyclopropane with gem-difluorine as an unconventional donor group undergoes (3 + 2)-cycloadditions with various aldehydes/ketones, affording densely functionalized gem-difluorotetrahydrofurans.     

A theoretical and computational study of the anion, neutral, and cation Cu(H(2)O) complexes

An ab initio investigation of the potential energy surfaces and vibrational energies and wave functions of the anion, neutral, and cation Cu(H(2)O) complexes is presented. The equilibrium geometries and harmonic frequencies of the three charge states of Cu(H(2)O) are calculated at the MP2 level of theory. CCSD(T) calculations predict a vertical electron detachment energy for the anion complex of 1.65 eV and a vertical ionization potential for the neutral complex of 6.27 eV. Potential energy surfaces are calculated for the three charge states of the copper-water complexes. These potential energy surfaces are used in variational calculations of the vibrational wave functions and energies and from these, the dissociation energies D(0) of the anion, neutral, and cation charge states of Cu(H(2)O) are predicted to be 0.39, 0.16, and 1.74 eV, respectively. In addition, the vertical excitation energies, that correspond to the 4 (2)P<--4 (2)S transition of the copper atom, and ionization potentials of the neutral Cu(H(2)O) are calculated over a range of Cu(H(2)O) configurations. In hydrogen-bonded, Cu-HOH configurations, the vertical excitation and ionization energies are blueshifted with respect to the corresponding values for atomic copper, and in Cu-OH(2) configurations where the copper atom is located near the oxygen end of water, both quantities are redshifted.     

Ionic photodissociation of some polymers quenched with electron donor or acceptor in solution

Ionic photodissociation processes of vinyl polymers with pendant carbazolyl groups in solution have been studied by nonsecond laser photolysis. The ionic dissociation yield decreases in the order of monomer, oligomers, and polymers.     

Solvent effects on the electron donor acceptor complex properties of ferrocene and tetranitromethane

Summary Spectral investigations in the 350–800 nm range of ferrocene (FcH) and tetranitromethane [C(NO₂)₄] solutions in cyclohexane and carbon tetrachloride at concentration-constant (FcH) and variable (tetranitromethane) were made. The electron donor acceptor (EDA) complex of ferrocene and tetranitromethane and its dissociation to the ferricenium cation (FcH⁺) were studied as a function of the solvent, the initial C(NO₂)₄ concentration and reaction time.     

Donor–acceptor (donor) polymers with differently conjugated side groups at the acceptor units for photovoltaics

Four new donor–acceptor (donor) [D–A(D)], PBDT‐PTQ, PBDT‐PTTQ, PBDT‐TQ, and PBDT‐TTQ, bearing the same backbone of alternative benzodithiophene (BDT) and quinoxaline units but with phenylene thienyl, phenylene di‐thienyl, thienyl and di‐thienyl groups (other donors), respectively, at the acceptor quinoxaline units, were designed and synthesized to investigate the impacts of the conjugated side chains at the acceptor units on the photovoltaic properties of polymers. The power conversion efficiencies (PCEs) of the polymer solar cells (PSCs) based on PBDT‐TQ:[6,6]‐phenyl‐C‐70‐butyric acid methyl ester (PC70BM) and PBDT‐PTQ:PC70BM reach to 4.39 and 3.58%, respectively, which are 43 and 17% higher, respectively, than that of a reported alkylphenyl substituted polymer with the same main chain. However, the PCEs based on PBDT‐TTQ and PBDT‐PTTQ, in which an additional thiophene is added at a side chain of PBDT‐TQ and PBDT‐PTQ, respectively, decline. The mechanism how the conjugated side chains affect the performance of the PSCs is also discussed. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013