Structure-property relationships in conjugated donor-acceptor molecules based on cyanoanthracene: computational and experimental studies

[reaction: see text] Two series of pi-conjugated bipolar compounds, namely, 9-phenyl-10-anthronitriles (PAN series) and 9-phenylethynyl-10-anthronitriles (PEAN series), having inherent redox centers have been synthesized and their electronic absorption, fluorescence emission, and electrochemical behavior have been studied. Electrochemiluminescence of these molecules bearing weak, strong, and spin-polarized donors is also studied. The observed electronic properties are explained with the help of results obtained from density functional theory (DFT- B3LYP/6-31G) calculations. The structure-property relationships of all the molecules are discussed.     

Electronic structure and optical properties of charged oligofluorenes studied by VIS/NIR spectroscopy and time-dependent density functional theory

The electronic structure and optical properties of charged oligofluorenes were studied experimentally and theoretically. Measurements of the optical absorption spectra of charged oligofluorenes in dilute solutions have been performed by using the pulse radiolysis technique. In addition, optical absorption spectra of radical cations and anions in a solid matrix were measured after gamma-irradiation at 77 K. The optical absorption spectra were measured in the range of 440-2100 nm (0.6-2.8 eV) and compared with results from time-dependent density functional theory (TDDFT) calculations. The calculated charge induced deformations and charge distribution do not indicate the occurrence of polaronic effects. The potential energy profiles for rotation around the inter-unit bond show that oligofluorenes are nonplanar in their neutral state, while they tend to more planar structures in their charged state. The optical absorption spectra of charged oligofluorenes are dependent on the angle between neighboring units. TDDFT absorption energies shift to lower values with increasing chain length, which suggests that the charge delocalizes along the oligomer chain.     

Structural and electronic properties of Si n, Si n+, and AlSi n-1 (n=2-13) clusters: theoretical investigation based on ab initio molecular orbital theory

The geometric and electronic structures of Si(n), Si(n) (+), and AlSi(n-1) clusters (2< or =n< or =13) have been investigated using the ab initio molecular orbital theory under the density functional theory formalism. The hybrid exchange-correlation energy function (B3LYP) and a standard split-valence basis set with polarization functions [6-31G(d)] were employed for this purpose. Relative stabilities of these clusters have been analyzed based on their binding energies, second difference in energy (Delta (2)E) and fragmentation behavior. The equilibrium geometry of the neutral and charged Si(n) clusters show similar structural growth. However, significant differences have been observed in the electronic structure leading to their different stability pattern. While for neutral clusters, the Si(10) is magic, the extra stability of the Si(11) (+) cluster over the Si(10) (+) and Si(12) (+) bears evidence for the magic behavior of the Si(11) (+) cluster, which is in excellent agreement with the recent experimental observations. Similarly for AlSi(n-1) clusters, which is isoelectronic with Si(n) (+) clusters show extra stability of the AlSi(10) cluster suggesting the influence of the electronic structures for different stabilities between neutral and charged clusters. The ground state geometries of the AlSi(n-1) clusters show that the impurity Al atom prefers to substitute for the Si atom, that has the highest coordination number in the host Si(n) cluster. The fragmentation behavior of all these clusters show that while small clusters prefers to evaporate monomer, the larger ones dissociate into two stable clusters of smaller size.     

Relativistic computational investigation: the geometries and electronic properties of TaSi(n)+ (n = 1-13, 16) clusters

The equilibrium geometries, stabilities, and electronic properties of the TaSi(n)+ (n = 1-13, 16) clusters are investigated systematically by using the relativistic density functional method with generalized gradient approximation. The small-sized TaSi(n)+ clusters with slight geometrical adjustments basically keep the frameworks that are analogous to the neutrals while the medium-sized charged clusters significantly deform the neutral geometries, which are confirmed by the calculated AIP and VIP values. Furthermore, the optimized geometries of the charged clusters agree with the experimental results of Hiura and co-workers (Hiura, H.; Miyazaki, T.; Kanayama, T. Phys. Rev. Lett. 2001, 86, 1733). The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gaps of the charged clusters are generally increased as the cluster size goes from n = 1 to 13; and the large HOMO-LUMO gaps of charged clusters resulting from the positive charge indicate that their chemical stabilities are stronger than their neutral counterparts, especially for n = 4, 6, and 7 clusters. Additionally, the contributions of the d orbitals of the Ta atom to the HOMO and LUMO reveal that the chemical activity of the d orbitals of the Ta atom decreases gradually as the number of silicon atoms increases. This interesting finding is in good agreement with the recent experimental results on the reactive activities of the H2O and transition-metal silicon clusters (Koyasu, K.; Akutsu, M.; Mitsui, M.; Nakajima, A. J. Am. Chem. Soc. 2005, 127, 4998). Generally, the positive charge significantly influences the electronic and geometric structures of the charged clusters. Finally, the most stable neutral and charged TaSi16 clusters are found to be fullerene-like structures and the HOMO-LUMO gap in charged form is detectable experimentally.     

负离子光电子能谱技术发展及应用

负离子光电子能谱已经成为探索光谱和化学动力学基础问题的最为重要的技术之一。本文简要介绍了负离子光电子能谱的发展历史,回顾了负离子光电子能谱发展过程中的几种主要技术,包括为了提高分辨率而开发出的零动能能谱和慢电子速度成像技术以及为在气相条件下研究多电荷负离子及其对应中性分子电子特性而开发的电喷雾源与负离子光电子能谱结合的技术。随后介绍其在锕系元素及化合物、含铍化合物的电子结构及成键特征研究中的应用及进展。     

A series of metal complexes with the non-innocent N,N'-bis(pentafluorophenyl)-o-phenylenediamido ligand: twisted geometry for tuning the electronic structure

A series of homoleptic complexes with non-innocent ligands derived from N,N'-bis(pentafluorophenyl)-o-phenylenediamine (H(2)(F)pda) are reported. [Ni(II)((F)sbqdi)(2)] (1), [Pd(II)((F)sbqdi)(2)] (2), [Co(II)((F)sbqdi)(2)] (3), and [Cu(II)((F)sbqdi)(2)] (4) were synthesized, where ((F)sbqdi)(1-) represents a radical anion formed by one-electron oxidation of the doubly deprotonated H2(F)pda. The oxidation states of ligands and metals in complexes 1-4 were assigned by single crystal X-ray crystallography performed at low temperatures. Complex 4 is the first Cu(II) complex where both o-phenylenediamine derived ligands are monoanionic radicals. The bulky N-C6F5 substituents force the complexes 1, 3, and 4 to adopt a twisted geometry (intermediate between square-planar and tetrahedral). The electronic structures of the neutral compounds 1-4 and of some of their cationic and/or anionic neighboring redox states were probed using EPR and UV-VIS-NIR spectroelectrochemistry. The twisted geometry of the complexes results in considerable changes in their electronic structures compared to the well known square-planar complexes while the strongly electron withdrawing N-C6F5 groups have a great influence on redox properties.     

Designer amphiphiles based on para-acyl-calix[8]arenes

The synthesis of a series of fully O-derivatised para-acyl-calix[8]arenes is described, where the acyl function is either octanoyl or hexadecanoyl. The groups attached at the phenolic face are, carboxymethoxy (anionic), carboxypropoxy (anionic), 4-sulfonatobutoxy (anionic), ethoxycarboxymethoxy (neutral), ethoxycarboxypropoxy (neutral), 2-methoxyethoxy (neutral) and 2-(2-methoxy)diethoxy (neutral). The use of specific synthetic routes has allowed complete substitution in high yields for all the compounds obtained. The interfacial properties of the compounds have been studied and stable monolayers have been obtained for certain compounds in the series having para-octanoyl substituents; all compounds studied in the series having para-hexadecanoyl substituents formed stable monolayers at the air-water interface. The interactions between O-4-sulfonatobutoxy-para-ocatanoylcalix[8]arene and a series of serum albumins have been studied by dynamic light scattering and specific adsorption of the calix-[8]-arene derivative onto the proteins observed. The anionic derivatives O-4-sulfonatobutoxy-para-ocatanoylcalix[8]arene and O-carboxymethoxy-para-ocatanoylcalix[8]arene have been shown to possess anticoagulant properties but to have no haemolytic toxicity.     

Acid properties of porphyrins and related systems

Structural, energetic, and electronic aspects of a series of porphyrins and related compounds in their neutral, anion, and dianion electronic states have been studied by means of DFT calculations [B3LYP/6-31+G(d,p)]. Analysis of the electron density puts forward a number of different kinds of interactions between the inner atoms. Intramolecular correlations similar to those found in intermolecular N-H···N interactions have been found. Published in Russian in Rossiiskii Khimicheskii Zhurnal, 2007, Vol. 51, No. 5, pp. 99–106.     

Photoelectron spectroscopy of doubly and singly charged group VIB dimetalate anions: M2O72-, MM'O72-, and M2O7- (M, M' = Cr, Mo, W)

We produced both doubly and singly charged Group VIB dimetalate species-M(2)O(7)(2-), MM'O(7)(2-), and M(2)O(7)(-) (M, M' = Cr, Mo, W)-using two different experimental techniques (electrospray ionization for the doubly charged anions and laser vaporization for the singly charged anions) and investigated their electronic and geometric structures using photoelectron spectroscopy and density functional calculations. Distinct changes in the electronic and geometric structures were observed as a function of the metal and charge state. The electron binding energies of the heteronuclear dianions MM'O(7)(2-) were observed to be roughly the average of those of their homonuclear counterparts (M(2)O(7)(2-) and M'(2)O(7)(2-)). Density functional calculations indicated that W(2)O(7)(2-), W(2)O(7)(-), and W(2)O(7) possess different ground-state structures: the dianion is highly symmetric (D(3d),(1)A(1g)) with a single bridging oxo ligand, the monoanion is a doublet (C(1), (2)A) with two bridging oxo ligands and a radical terminal oxo ligand, whereas the neutral is a singlet (C(1), (1)A) with two bridging oxo ligands and a terminal peroxo ligand. The combined experimental and theoretical study provides insights into the evolution of geometric and electronic structures as a function of charge state. The clusters identified might provide insights into the possible structures of reactive species present in early transition-metal oxide catalysts that are relevant to their reactivity and catalytic function.     

Theoretical study of chloropyrroles as monomers for new conductive polymers

Electronic, structural, electrochemical, and spectroscopic properties of all ground-state neutral and singly ionized chlorine-substituted pyrroles and hexa(3-chloropyrrole) oligomer are studied using the density functional theory B3LYP method with the 6-31G(d,p) basis set. The effects of the number and position of the substituents on the electrochemical properties of the pyrrole ring have been studied and analyzed both quantitatively and qualitatively. By using the optimized structures obtained for these molecules and their cations, IR and NMR spectra have been predicted. The results of this study, including spin and charge distributions, show that, among all of these compounds, 3-chloropyrrole has the most suitable conditions for electropolymerization.     

Electronic modulation of dithienothiophene (DTT) as pi-center of D-pi-D chromophores on optical and redox properties: analysis by UV-Vis-NIR and Raman spectroscopies combined with electrochemistry and quantum chemical DFT calculations

In this paper, we study three symmetrical D-pi-D chromophores containing dithieno[3,2-b:2',3'-d]thiophene (DTT) as the pi-center and various donor end moieties, by means of UV-vis-NIR and FT-Raman spectroscopy and in situ spectroelectrochemistry. The compounds display dual redox properties: all exhibited two oxidations and single stable reduction peaks contrarily to the one or two oxidations and none reduction which could be anticipated in view of their chemical structures. We analyze the possible electronic modulation by the pi-conjugated DTT relay in the redox process and electronic coupling between the two electron donor (D) units attached through conjugation to opposite sides of the pi-linker. To this end, the UV-vis-NIR and FT-Raman spectra of the neutral compounds and of the charged species generated upon in situ p- or n-doping have been recorded and interpreted with the help of Density Functional Theory (DFT) calculations. The analysis of the peculiar Raman features of these pi-conjugated chromophores is guided by the formalism of the Effective Conjugation Coordinate (ECC) theory. This research shows that the Raman spectroscopic characterization of this type of D-pi-D structures is a powerful tool to derive information about their pi-conjugational properties in the pristine and doped states.     

Molecular and electronic structures of bis(pyridine-2,6-diimine)metal complexes [ML2](PF6)n (n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni, Cu, Zn)

A series of mononuclear, octahedral first-row transition metal ion complexes mer-[M(II)L0(2)](PF6)2 containing the tridentate neutral ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L0) and a Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II) ion have been synthesized and characterized by X-ray crystallography. Cyclic voltammetry and controlled potential coulometry show that each dication (except those of Cu(II) and Zn(II)) can be reversibly one-electron-oxidized, yielding the respective trications [M(III)L0(2)]3+, and in addition, they can be reversibly reduced to the corresponding monocations [ML2]+ and the neutral species [ML2]0 by two successive one-electron processes. [MnL2]PF6 and [CoL2]PF6 have been isolated and characterized by X-ray crystallography; their electronic structures are described as [Mn(III)L1(2)]PF6 and [Co(I)L0(2)]PF6 where (L1)1- represents the one-electron-reduced radical form of L0. The electronic structures of the tri-, di-, and monocations and of the neutral species have been elucidated in detail by a combination of spectroscopies: UV-vis, NMR, X-band EPR, Mossbauer, temperature-dependent magnetochemistry. It is shown that pyridine-2,6-diimine ligands are noninnocent ligands that can be coordinated to transition metal ions as neutral L0 or, alternatively, as monoanionic radical (L1)1-. All trications are of the type [M(III)L0(2)]3+, and the dications are [M(II)L0(2)]2+. The monocations are described as [Mn(III)L1(2)]+ (S = 0), [Fe(II)L0L1]+ (S = 1/2), [Co(I)L0(2)]+ (S = 1), [Ni(I)L0(2)]+ (S = 1/2), [Cu(I)L0(2)]+ (S = 0), [Zn(II)L1L0]+ (S = 1/2) where the Mn(II) and Fe(II) ions are low-spin-configurated. The neutral species are described as [Mn(II)L1(2)]0, [Fe(II)L1(2)]0, [Co(I)L0L1]0, [Ni(I)L0L1]0, and [Zn(II)L1(2)]0; their electronic ground states have not been determined.     

Aromaticity and electronic delocalization in all-metal clusters with single, double, and triple aromatic character

A series of monocyclic planar inorganic compounds with single, double, and triple (anti)aromatic character has been studied. The electron delocalization and aromaticity of these compounds have been assessed by means of two-center and multicenter electronic delocalization indices and their ??-, ??-, and ??-components. Results show that these indices are excellent predictors of the ??-, ??-, and ??-aromatic character of all-metal and semimetal clusters.     

Theoretical study of mixed silicon-lithium clusters Si(n)Li(p)(+) (n=1-6, p=1-2)

Theoretical study on the structures of neutral and singly charged Si(n)Li(p)((+)) (n=1-6, p=1-2) clusters have been carried out in the framework of the density functional theory (DFT) with the B3LYP functional. The structures of the neutral Si(n)Li(p) and cationic Si(n)Li(p)(+) clusters are found to keep the frame of the corresponding Si(n), Li species being adsorbed at the surface. The localization of the lithium cation is not the same one as that of the neutral atom. The Li(+) ion is preferentially located on a Si atom, while the Li atom is preferentially attached at a bridge site. A clear parallelism between the structures of Si(n)Na(p) and those of Si(n)Li(p) appears. The population analysis show that the electronic structure of Si(n)Li(p) can be described as Si(n)(p)(-)+pLi(+) for the small sizes considered. Vertical and adiabatic ionization potentials, adsorption energies, as well as electric dipole moments and static dipolar polarizabilities, are calculated for each considered isomer of neutral species.     

Synthesis and electrogenerated chemiluminescence of donor-substituted phenylethynylcoumarins

Two series of donor-bearing phenylethynylcoumarins have been synthesized, and their photophysical properties have been evaluated. Chemiluminescence was observed through the annihilation of their electrogenerated radical ions and was found to be only slightly affected by the presence of various donor groups on the phenyl moiety linked through the C-C triple bond. The overall properties of the two series of compounds are discussed with respect to their structures. The observed electronic absorption properties are explained with the help of computational studies.     

Interaction of dicarboxylic metalloporphyrins with liposomes. The effect of pH on membrane binding revisited

The acid-base properties of Zn-hematoporphyrin IX (ZnHP) and Zn-mesoporphyrin IX (ZnMP) and the effect of pH on their binding to liposomes have been studied. The ionization constants for the two carboxylate groups of ZnHP were calculated by principal component analysis and are 5.7 +/- 0.1 and 6.9 +/- 0.05. The neutral species and the mono- and dianionic forms all bind to liposomes, but a strong pH effect on the binding constant was observed for both the investigated compounds. We also observed a decrease in the binding of the two anionic species when the membranes carried a negative charge. These results indicate that the porphyrins partition into the membrane with their carboxylic moieties near the lipid-water interface so that their deprotonation, leading to a charged molecule, does not prevent the insertion of the tetrapyrrole ring into the lipid environment of neutral liposomes.     

Germanium,carbon‐germanium,and silicon‐germanium triangulenes

A series of germanium‐containing triangular molecules have been studied by density functional theory (DFT) calculations. The triangulene topology of the compounds provides for their high‐spin ground states and strong sign alternation of spin density and atomic charge distributions. High values of the exchange coupling constants witness ferromagnetic ordering of electronic structures of all studied triangulenes. The compounds bearing more electronegative atoms in a‐positions of the triangular networks possess higher aromatic character and stronger ferromagnetic ordering. © 2015 Wiley Periodicals, Inc.     

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.