One‐, two‐, and three‐electron bonding: An “in vitro” theoretical study using noninteger nuclear charges evidences the crucial role of electronegativity in the strength of symmetrical bonds

Fictitious hydrogen atoms H*_A of variable nuclear charge 0.5 ≤ Z_A ≤ 2 (and thus of variable electronegativity) are used to study the intrinsic dependency of chemical bonding on electronegativity. Dissociation energy and equilibrium distance are reported for symmetrical 1‐, 2‐ and 3‐electron H*_AH*_A systems and 2‐electron dissymmetrical H*_A‐H ones. Dealing with symmetrical systems, the strongest two‐electron bonds are found for Z_A ≈ 1.2. Oneelectron and three‐electron strongest bonds occur respectively with low (ca. 0.7) and high (ca. 1.7) Z_A values and can become stronger than the corresponding 2‐electron system. Comparison with data on real systems leads to conclude that electronegativity is a prevailing atomic property in the control of the dissociation energy of symmetrical 1‐, 2‐ and 3‐electron bonds. A simplified mathematical model at Hartree‐Fock or Heitler‐London level with a minimal basis set reproduces these trends semi‐quantitatively and provides the overall shape of the dissociation curves. Finally some points are qualitatively discussed from MO analysis, which emphasize the dependence of the bonding/antibonding properties on the nucleus charge Z_A and their occupancy number. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Simultaneous evaluation of one‐electron reducing systems and radical reactions in cells by nitroxyl biradical as probe

In the present study, a novel probe for the simultaneous evaluation of one‐electron reducing systems (electron transport chain) and one‐electron oxidizing systems (free radical reactions) in cells by electron chemical detection was developed. Six‐membered cyclic nitroxyl radicals (2,2,6,6‐tetramethylpiperidine‐1‐oxyl; TEMPO series) are sensitive to one‐electron redox systems, generating the hydroxylamine form [TEMPO(H)] via one‐electron reduction, and the secondary amine form [TEMPO(N)] via one‐electron oxidation in the presence of thiols. In contrast, the sensitivities of five‐membered cyclic nitroxyl radicals (2,2,5,5‐tetramethylpyrrolidine‐1‐oxyl; PROXYL series) to the one‐electron redox systems are comparatively low. The electron chemical detector can detect 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), TEMPO(H) and PROXYL but not TEMPO(N). Therefore, nitroxyl biradical, TEMPO‐PROXYL, as a probe for the evaluation of one‐electron redox systems was employed. TEMPO‐PROXYL was synthesized by the conjunction of 4‐amino‐TEMPO with 3‐carboxyl‐PROXYL via the conventional dicyclohexyl carbodiimide reaction. TEMPO‐PROXYL, TEMPO(H)‐PROXYL and TEMPO(N)‐PROXYL were simultaneously quantified by HPLC with Coularray detection. Calibration curves for the quantification of TEMPO‐PROXYL, TEMPO(H)‐PROXYL and TEMPO(N)‐PROXYL were linear in the range from 80 nm to 80 μm , and the lowest quantification limit of each molecule was estimated to be <80 nm . The relative standard deviations at 0.8 and 80 μm were within 10% (n = 5). Copyright © 2015 John Wiley & Sons, Ltd.     

Electron attachment to the DNA bases adenine and guanine and dehydrogenation of their anionic derivatives: Density functional study

Density functional theory (DFT) calculations have been used to explore electron attachment to the purines adenine and guanine and their hydrogen atom loss. Calculations show that the dehydrogenation at the N9 site in the adenine and guanine transient anions is the lowest‐cost channel of hydrogen loss, and the N9? H bond scission has Gibbs free energies of dissociation ΔG° of 8.8 kcal mol^?1 for the anionic adenine and 13.9 kcal mol^?1 for the anionic guanine. The relatively high feasibility of low‐energy electron (LEE)‐induced N9? H bond cleavage in the purine nucleobases arises from high electron affinities of their H‐deleted counterparts. Unlike adenine, other N? H bond dissociations are competitive with the N9? H bond fission in the anionic guanine. The replacement of hydrogen in the ring of purine has a significant effect on the N9? H bond fragmentation. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Photoinduced Electron Transfer Reactions of 3,3‐Dialkylated 4,5‐Diphenyl‐3H‐Pyrazoles: A New Route to the Formation of the Solvent Adducts

3,3‐Dialkyl‐4,5‐diphenyl‐3H‐pyrazoles undergo readily photoinduced electron transfer (PET) reaction with 2,4,6‐triphenylpyrylium tetrafluoroborate (TPP⁺) in acetonitrile to produce cyclopropenes and 2H‐pyrroles. During prolonged irradiation, the new ring‐closure products derived from 2H‐pyrroles as the secondary photoproducts are also produced. However, the corresponding ester analog exhibits different behavior to obtain the cyclopropene as the primary photoproduct and a [2+2] dimer of the cyclopropene as the secondary photoproduct. A rationale for the different behavior is offered.     

Three‐Dimensional Structure of Olefinic Thermoplastic Elastomer Blends Using Electron Tomography

Summary: The present communication reports the first use of electron tomography in reconstructing the three‐dimensional morphology in thermoplastic elastomer blends. The blends investigated were dynamically vulcanized blends of ethylene‐propylene‐diene (EPDM) rubber/poly(propylene)/oil and polystyrene‐block‐(ethylene‐co‐butylene)‐block‐polystyrene (SEBS)/poly(propylene)/oil. An easy identification of blend morphology could be carried out at blend compositions, where conventional transmission electron microscopic imaging gives misleading information. This technique gives a higher resolution than any other microscopic technique, and is applicable to blends with dispersed as well as co‐continuous morphologies.

Example of a tomographic model of partially co‐continuous SEBS phases in a SEBS/PP/oil thermoplastic blend. Only the contours of the SEBS phase are shown.     

Electron Attachment to Solvated dGpdG: Effects of Stacking on Base‐Centered and Phosphate‐Centered Valence‐Bound Radical Anions

To explore the nature of electron attachment to guanine‐centered DNA single strands in the presence of a polarizable medium, a theoretical investigation of the DNA oligomer dinucleoside phosphate deoxyguanylyl‐3′,5′‐deoxyguanosine (dGpdG) was performed by using density functional theory. Four different electron‐distribution patterns for the radical anions of dGpdG in aqueous solution have been located as local minima on the potential energy surface. The excess electron is found to reside on the proton of the phosphate group (dGp^H?dG), or on the phosphate group (dGp^.?dG), or on the nucleobase at the 5′ position (dG^.?pdG), or on the nucleobase at the 3′ position (dGpdG^.?), respectively. These four radical anions are all expected to be electronically viable species under the influence of the polarizable medium. The predicted energetics of the radical anions follows the order dGp^.?dG>dG^.?pdG>dGpdG^.?>dGp^H?dG. The base–base stacking pattern in DNA single strands seems unaffected by electron attachment. On the contrary, intrastrand H‐bonding is greatly influenced by electron attachment, especially in the formation of base‐centered radical anions. The intrastrand H‐bonding patterns revealed in this study also suggest that intrastrand proton transfer might be possible between successive guanines due to electron attachment to DNA single strands.     

Theoretical study of the red‐ and blue‐shifted hydrogen bonds of nitroxyl and acetylene dimers

Ab initio molecular orbital and density functional theory (DFT) in conjunction with different basis sets calculations were performed to study the C? H…O red‐shifted and N? H…π blue‐shifted hydrogen bonds in HNO? C₂H₂ dimers. The geometric structures, vibrational frequencies and interaction energies were calculated by both standard and counterpoise (CP)‐corrected methods. In addition, the G3B3 method was employed to calculate the interaction energies. The topological and natural bond orbital (NBO) analysis were investigated the origin of N? H…π blue‐shifted hydrogen bond. From the NBO analysis, the electron density decrease in the σ* (N? H) is due to the significant electron density redistribution effect. The blue shifts of the N? H stretching frequency are attributed to a cooperative effect between the rehybridization and electron density redistribution. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Interaction of the important species HNO and HFSO2 in the atmosphere: Theoretical study of the N?H and S?H blue‐shifted hydrogen bonds

Ab initio molecular orbital and density functional theory (DFT) in conjunction with different basis sets calculations were performed to study the N? H…O and S? H…O blue‐shifted H‐bonds in the HNO…HFSO₂ complex. The geometric structures, vibrational frequencies, and interaction energies were calculated by both standard and CP‐corrected methods. Natural bond orbital (NBO) analysis was used to investigate the origin of blue‐shifted H‐bonds, showing that the decrease in the σ*(N? H) and σ*(S? H) is due to the electron density redistribution effect. The structure reorganization effect on the blue‐shifted hydrogen bonds was discussed in detail. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Interactions of Amino Acids with Oxidized Guanine in the Gas Phase Associated with the Protection of Damaged DNA

Density functional theory calculations were employed to study the stabilization process of the guanine radical cation through amino acid interactions as well as to understand the protection mechanisms. On the basis of our calculations, several protection mechanisms are proposed in this work subject to the type of the amino acid. Our results indicate that a series of three‐electron bonds can be formed between the amino acids and the guanine radical cation which may serve as relay stations supporting hole transport. In the three‐electron‐bonded, π–π‐stacked, and H‐bonded modes, amino acids can protect guanine from oxidation or radiation damage by sharing the hole, while amino acids with reducing properties can repair the guanine radical cation through proton‐coupled electron transfer or electron transfer. Another important finding is that positively charged amino acids (ArgH⁺, LysH⁺, and HisH⁺) can inhibit ionization of guanine through raising its ionization potential. In this situation, a negative dissociation energy for hydrogen bonds in the hole‐trapped and positively charged amino acid–Guanine dimer is observed, which explains the low hole‐trapping efficiency. We hope that this work provides valuable information on how to protect DNA from oxidation‐ or radiation‐induced damages in biological systems.     

Size- and shape-dependent activity of metal nanoparticles as hydrogen-evolution catalysts: mechanistic insights into photocatalytic hydrogen evolution

The catalytic activity of Pt nanoparticles (PtNPs) with different sizes and shapes was investigated in a photocatalytic hydrogen‐evolution system composed of the 9‐mesityl‐10‐methylacridinium ion (Acr⁺–Mes: photocatalyst) and dihydronicotinamide adenine dinucleotide (NADH: electron donor), based on rates of hydrogen evolution and electron transfer from one‐electron‐reduced species of Acr⁺–Mes (Acr^.–Mes) to PtNPs. Cubic PtNPs with a diameter of (6.3±0.6) nm exhibited the maximum catalytic activity. The observed hydrogen‐evolution rate was virtually the same as the rate of electron transfer from Acr^.–Mes to PtNPs. The rate constant of electron transfer (k_et) increased linearly with increasing proton concentration. When H⁺ was replaced by D⁺, the inverse kinetic isotope effect was observed for the electron‐transfer rate constant (k_et(H)/k_et(D)=0.47). The linear dependence of k_et on proton concentration together with the observed inverse kinetic isotope effect suggests that proton‐coupled electron transfer from Acr^.–Mes to PtNPs to form the Pt? H bond is the rate‐determining step for catalytic hydrogen evolution. When FeNPs were used instead of PtNPs, hydrogen evolution was also observed, although the hydrogen‐evolution efficiency was significantly lower than that of PtNPs because of the much slower electron transfer from Acr^.–Mes to FeNPs.     

Molecular Conductance through a Quadruple‐Hydrogen‐Bond‐Bridged Supramolecular Junction

A series of self‐complementary ureido pyrimidinedione (UPy) derivatives modified with different aurophilic anchoring groups were synthesized. Their electron transport properties through the quadruple hydrogen bonds in apolar solvent were probed employing the scanning tunneling microscopy break junction (STMBJ) technique. The molecule terminated with a thiol shows the optimal electron transport properties, with a statistical conductance value that approaches 10^?3 G₀. The ¹H NMR spectra and control experiments verify the formation of quadruple hydrogen bonds, which can be effectively modulated by the polarity of the solvent environment. These findings provide a new design strategy for supramolecular circuit elements in molecular electronics.     

Quantum chemistry aspects of the solvent effects on the ene reaction of 1‐Phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene

A density functional theory study was used to investigate the quantum aspects of the solvent effects on the kinetic and mechanism of the ene reaction of 1‐phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene. Using the B3LYP/6–311++ G(d,p) level of the theory, reaction rates have been calculated in the various solvents and good agreement with the experimental data has been obtained. Natural bond orbital analysis has been applied to calculate the stabilization energy of N18? H19 bond during the reaction. Topological analysis of quantum theory of atom in molecule (QTAIM) studies for the electron charge density in the bond critical point (BCP) of N18? H19 bond of the transition states (TSs) in different solvents shows a linear correlation with the interaction energy. It is also seen form the QTAIM analysis that increase in the electron density in the BCP of N18? H19, raises the corresponding vibrational frequency. Average calculated ratio of 0.37 for kinetic energy density to local potential energy density at the BCPs as functions of N18? H19 bond length in different media confirmed covalent nature of this bond. Using the concepts of the global electrophilicity index, chemical hardness and electronic chemical potentials, some correlations with the rate constants and interaction energy have been established. Mechanism and kinetic studies on 1‐phenyl‐1,3,4‐triazolin‐2,5‐dione and 2‐methyl‐2‐butene ene reaction suggests that the reaction rate will boost with interaction energy enhancement. Interaction energy of the TS depends on the solvent nature and is directly related to electron density of the bonds involved in the reaction proceeding, global electrophilicity index and electronic chemical potential. However, the chemical hardness relationship is reversed. Finally, an interesting and direct correlation between the imaginary vibrational frequency of the N18? H19 critical bond and its electron density at the TS has been obtained. © 2014 Wiley Periodicals, Inc.     

Transition metals as electron traps. I. Structures,energetics, electron capture,and electron‐transfer‐induced dissociations of ternary copper–peptide complexes in the gas phase

Electron‐induced dissociations of gas‐phase ternary copper‐2,2′‐bipyridine complexes of Gly‐Gly‐Gly and Gly‐Gly‐Leu were studied on a time scale ranging from 130 ns to several milliseconds using a combination of charge‐reversal (⁺CR^?) and electron‐capture‐induced dissociation (ECID) measured on a beam instrument and electron capture dissociation (ECD) measured in a Penning trap. Charge‐reduced intermediates were observed on the short time scale in the ⁺CR^? and ECID experiments but not in ECD. Ion dissociations following electron transfer or capture mostly occurred by competitive bpy or peptide ligand loss, whereas peptide backbone fragmentations were suppressed in the presence of the ligated metal ion. Extensive electron structure theory calculations using density functional theory and large basis sets provided optimized structures and energies for the precursor ions, charge‐reduced intermediates, and dissociation products. The Cu complexes underwent substantial structure changes upon electron capture. Cu was calculated to be pentacoordinated in the most stable singly charged complexes of the [Cu(peptide ? H)bpy]^{+ ?} type where it carried a ～+ 1 atomic charge. Cu coordination in charge‐reduced [Cu(peptide ? H)bpy] intermediates depended on the spin state. The themodynamically more stable singlet states had tricoordinated Cu, whereas triplet states had a tetracoordinated Cu. Cu was tricoordinated in stable [Cu(peptide ? H)bpy]^{? ?} products of electron transfer. [Cu(peptide)bpy]^{2 + ?} complexes contained the peptide ligand in a zwitterionic form while Cu was tetracoordinated. Upon electron capture, Cu was tri‐ or tetracoordinated in the [Cu(peptide)bpy]⁺ charge‐reduced analogs and the peptide ligands underwent prototropic isomerization to canonical forms. The role of excited singlet and triplet electronic states is assessed. Copyright © 2009 John Wiley & Sons, Ltd.     

The electron microanalyzer (EPMA): a powerful device for the microanalysis of filled polymeric materials

The electron probe microanalyzer is a device often used in the field of geology or in the glass and steel industries. However, it is barely known or used in the polymer field. Thus, in this paper, we investigate the use of electron probe microanalyzer for polymer microanalyses and compared it with a scanning electron microscope equipped with an energy dispersive spectrometer. To show the unique potential of this technique only develop in our lab for polymer application, three different samples were studied: (i) a fire protective epoxy‐based coating submitted to aging in salt water, (ii) the distribution of organometallic catalysts into a thermal isolative silicone polymer, and (iii) the fouling growth of milk protein (biopolymer) on a stainless steel surface. Compared to an energy dispersive spectrometer, with an electron probe microanalyzer it is possible to quickly create X‐ray mappings of low concentration elements at a good resolution, as well as allowing the interpretation of the mechanism of action for the three samples which was impossible using only an energy dispersive spectrometer because of its too low detection resolution. Copyright © 2015 John Wiley & Sons, Ltd.     

Photophysical Analysis of 1,10‐Phenanthroline‐Embedded Porphyrin Analogues and Their Magnesium(II) Complexes

The synthesis, characterization, photophysical properties, and theoretical analysis of a series of tetraaza porphyrin analogues ( H? Pn : n=1–4) containing a dipyrrin subunit and an embedded 1,10‐phenanthroline subunit are described. The meso‐phenyl‐substituted derivative ( H? P1 ) interacts with a Mg²⁺ salt (e.g., MgCl₂, MgBr₂, MgI₂, Mg(ClO₄)₂, and Mg(OAc)₂) in MeCN solution, thereby giving rise to a cation‐dependent red‐shift in both the absorbance‐ and emission maxima. In this system, as well as in the other H? Pn porphyrin analogues used in this study, the four nitrogen atoms of the ligand interact with the bound magnesium cation to form Mg²⁺–dipyrrin–phenanthroline complexes of the general structure MgX? Pn (X=counteranion). Both single‐crystal X‐ray diffraction analysis of the corresponding zinc‐chloride derivative ( ZnCl? P1 ) and fluorescence spectroscopy of the Mg‐adducts that are formed from various metal salts provide support for the conclusion that, in complexes such as MgCl? P1 , a distorted square‐pyramidal geometry persists about the metal cation wherein a chloride anion acts as an axial counteranion. Several analogues ( H? Pn ) that contain electron‐donating and/or electron‐withdrawing dipyrrin moieties were prepared in an effort to understand the structure–property relationships and the photophysical attributes of these Mg–dipyrrin complexes. Analysis of various MgX? Pn (X=anion) systems revealed significant substitution effects on their chemical, electrochemical, and photophysical properties, as well as on the Mg²⁺‐cation affinities. The fluorescence properties of MgCl? Pn reflected the effect of donor‐excited photoinduced electron transfer (d‐PET) processes from the dipyrrin subunit (as a donor site) to the 1,10‐phenanthroline acceptor subunit. The proposed d‐PET process was analyzed by electron paramagnetic resonance (EPR) spectroscopy and by femtosecond transient absorption (TA) spectroscopy, as well as by theoretical DFT calculations. Taken together, these studies provide support for the suggestion that a radical species is produced as the result of an intramolecular charge‐transfer process, following photoexcitation. These photophysical effects, combined with a mixed dipyrrin–phenanthroline structure that is capable of effective Mg²⁺‐cation complexation, lead us to suggest that porphyrin‐inspired systems, such as H? Pn , have a role to play as magnesium‐cation sensors.     

New Tools for Investigating Electromagnetic Hot Spots in Single‐Molecule Surface‐Enhanced Raman Scattering

Surface‐enhanced Raman scattering (SERS) is quickly growing as an analytical technique, because it offers both molecular specificity and excellent sensitivity. For select substrates, SERS can even be observed from single molecules, which is the ultimate limit of detection. This review describes recent developments in the field of single‐molecule SERS (SM‐SERS) with a focus on new tools for characterizing SM‐SERS‐active substrates and how they interact with single molecules on their surface. In particular, techniques that combine optical spectroscopy and microscopy with electron microscopy are described, including correlated optical and transmission electron microscopy, correlated super‐resolution imaging and scanning electron microscopy, and correlated optical microscopy and electron energy loss spectroscopy.     

New low band‐gap semiconducting polymers consisting of 5‐(9H‐carbazol‐9‐yl)benzo[a]phenazine as a new acceptor unit for organic photovoltaic cells

A new carbazole‐based electron accepting unit, 5‐(2,7‐dibromo‐9H‐carbazol‐9‐yl)benzo[a]phenazine (CBP), was newly designed and synthesized as the acceptor part of donor‐acceptor type low band‐gap polymers for polymer solar cells. The CBP was copolymerized with electron donating monomers such as benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(2‐octyl‐2‐thienyl)‐benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) through Stille cross‐coupling polymerization, and produced two alternating copolymers, PBDT‐CBP and PBDTT‐CBP. An alternating copolymer (PBDT‐CBZ) consisted of 2,7‐dibromo‐9‐(heptadecan‐9‐yl)‐9H‐carbazole (CBZ) and BDT units was also synthesized for comparison. PBDT‐CBZ showed the maximum absorption at 430 nm and did not show absorption at wavelengths longer than 513 nm. However, CBP containing polymers (PBDT‐CBP and PBDTT‐CBP) showed a broad absorption between 300 and 850 nm due to the intramolecular charge transfer interaction between the electron donating and accepting blocks in the polymeric backbone. Bulk heterojunction photovoltaic devices were fabricated using the synthesized polymers as electron donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as electron acceptor. One of these devices showed a power conversion efficiency of 2.33%, with an open‐circuit voltage of 0.81 V, a short‐circuit current of 6.97 mA/cm², and a fill factor (FF) of 0.41 under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW/cm²). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 2354–2365     

The Equally Important Role of Adenine Derivatives to That of Pyrimidine Derivatives in Near‐0 eV Electron‐Induced DNA Lesions

The role of adenine (A) derivatives in DNA damage is scarcely studied due to the low electron affinity of base A. Experimental studies demonstrate that low‐energy electron (LEE) attachment to adenine derivatives complexed with amino acids induces barrier‐free proton transfer producing the neutral N₇‐hydrogenated adenine radicals rather than conventional anionic species. To explore possible DNA lesions at the A sites under physiological conditions, probable bond ruptures in two models—N₇‐hydrogenated 2′‐deoxyadenosine‐3′‐monophosphate (3′‐dA(N7H)MPH) and 2′‐deoxyadenosine‐5′‐monophosphate (5′‐dA(N7H)MPH), without and with LEE attachment—are studied by DFT. In the neutral cases, DNA backbone breakage and base release resulting from C_3′?O_3′ and N₉?C_1′ bond ruptures, respectively, by an intramolecular hydrogen‐transfer mechanism are impossible due to the ultrahigh activation energies. On LEE attachment, the respective C_3′?O_3′ and N₉?C_1′ bond ruptures in [3′‐dA(N7H)MPH]^? and [5′‐dA(N7H)MPH]^? anions via a pathway of intramolecular proton transfer (PT) from the C_2′ site of 2′‐deoxyribose to the C₈ atom of the base moiety become effective, and this indicates that substantial DNA backbone breaks and base release can occur at non‐3′‐end A sites and the 3′‐end A site of a single‐stranded DNA in the physiological environment, respectively. In particular, compared to the results of previous theoretical studies, not only are the electron affinities of 3′‐dA(N7H)MPH and 5′‐dA(N7H)MPH comparable to those of hydrogenated pyrimidine derivatives, but also the lowest energy requirements for the C_3′?O_3′ and N₉‐glycosidic bond ruptures in [3′‐dA(N7H)MPH]^? and [5′‐dA(N7H)MPH]^? anions, respectively, are comparable to those for the C_3′?O_3′ and N₁‐glycosidic bond cleavages in corresponding anionic hydrogenated pyrimidine derivatives. Thus, it can be concluded that the role of adenine derivatives in single‐stranded DNA damage is equally important to that of pyrimidine derivatives in an irradiated cellular environment.     

Hydrogen Bonding Interaction of Formic Acid-, Formaldehyde-, Formylfluoride-Nitrosyl Hydride： Theoretical Study on the Geometries, Interaction Energies and Blue- or Red-Shifted Hydrogen Bonds

The hydrogen bonding interaction of formic acid-, formaldehyde-, formylfluoride-nitrosyl hydride complexes was investigated by the density functional theory （DFT） and ab inito method in conjunction with 6-311＋＋G（2d,2p） basis set. The geometries, vibrational frequencies and interaction energies of the complexes were calculated by both standard and CP-corrected methods respectively. Moreover, G3B3 method was employed to estimate the interaction energies. There are C--H…O, N--H…O, N--H…F blue-shifted H-bonds and red-shifted O----H…O H-bond in the complexes. Electron density redistribution and rehybridization contribute to the N--H and C--H blue shifts. All geometric reorganizations contribute to the N--H blue shifts and partial geometric reorganizations contribute to the C--H blue shifts. The geometric reorganizations of the complex C except ZH（5）-O（4）-C（1） contribute to the O----H red shift. For the N--H blue shifts, the effect of r（N--O） variation on the N--H blue shifts is larger than that of ZH-N-O variation. Rehybridization plays a dominant role in the degree of N--H blue shifts, whereas the electron density redistribution contributes more to the degree of C--H blue shifts than the other effects do.     

Unprecedented Nucleophilic Attack of Piperidine on the Electron Acceptor during the Synthesis of Push‐Pull Dyes by a Knoevenagel Reaction

An unprecedented nucleophilic addition of piperidine on an electron acceptor, namely, 2‐(3‐oxo‐2,3‐dihydro‐1H‐cyclopenta[b]naphthalen‐1‐ylidene)malononitrile is reported. This unexpected behavior was observed during the synthesis of push‐pull dyes using the classical Knoevenagel reaction. To overcome this drawback, use of diisopropylethylamine (DIPEA) enabled to produce the expected dyes PP1 and PP2 . The optical and electrochemical properties of the different dyes were examined. Theoretical calculations were also carried out to support the experimental results. To evidence the higher electron‐withdrawing ability of this electron acceptor, a comparison was established with two dyes ( PP3 and PP4 ) comprising its shorter analogue.