Photoinduced Electron Transfer within a Zinc Porphyrin–Cyclobis(paraquat‐p‐phenylene) Donor–Acceptor Dyad

Understanding the mechanism of efficient photoinduced electron‐transfer processes is essential for developing molecular systems for artificial photosynthesis. Towards this goal, we describe the synthesis of a donor–acceptor dyad comprising a zinc porphyrin donor and a tetracationic cyclobis(paraquat‐p‐phenylene) (CBPQT⁴⁺) acceptor. The X‐ray crystal structure of the dyad reveals the formation of a dimeric motif through the intermolecular coordination between the triazole nitrogen and the central Zn metal of two adjacent units of the dyad. Photoinduced electron transfer within the dyad in MeCN was investigated by femtosecond and nanosecond transient absorption spectroscopy, as well as by transient EPR spectroscopy. Photoexcitation of the dyad produced a weakly coupled ZnP^+.–CBPQT^3+. spin‐correlated radical‐ion pair having a τ=146 ns lifetime and a spin–spin exchange interaction of only 0.23 mT. The long radical‐ion‐pair lifetime results from weak donor–acceptor electronic coupling as a consequence of having nine bonds between the donor and the acceptor, and the reduction in reorganization energy for electron transfer caused by charge dispersal over both paraquat units within CBPQT^3+..     

Effect of water on zinc (II), cadmium (II) complexes with pyridylimidazole: Theoretical study of stability and electronic spectrum

The geometry structures of complexes such as [Zn(PIm)₂(H₂O)] and [Cd(PIm)₂(H₂O)₂] [PIm = (2‐(2′‐pyridyl) imidazole)] are optimized by density functional theory (DFT) B3LYP methods. On the basis of their stable structures, the stability of the coordinated water existing in the complexes is analyzed quantitatively in terms of the interaction between the central metal and the coordinated water. The interaction energy of the Zn pyridylimidazole complex increased obviously by considering the intermolecular hydrogen bond (O? H…N). The theoretical calculation well explained penta‐ and hexa‐coordinated conformation, respectively, in Zn and Cd pyridylimidazole complexes. The spectral properties of the Zn Cd complexes have been studied by time‐dependent density functional theory (TD‐DFT). The calculation results show that the coordinated waters in Cd complexes have little effect on their spectral properties. While the axially coordinated waters in Zn pyridylimidazole cause a red shift in the absorption wavelength and change the pattern of charge transfer as a result of the effect of polarization from intermolecular hydrogen bond. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Dual‐emissive polydiphenylsilane nanocomposite: effect of N,N′‐bis(4‐hydroxysalicylidene)‐1,2‐phenylenediamine‐Zn complex

The fluorescence properties of polysilane can be strongly influenced by creating new excited states that involve electronic transitions and the relaxation to the ground state. This work presents the optical effects obtained by doping a specially designed polydiphenylsilane copolymer with Zn complex of N,N′‐bis(4‐hydroxysalicylidene)‐1,2‐phenylenediamine. The nanocomposites have been prepared in solution by mixing the polymer with low amounts of Zn–salophen and using tetrahydrofuran as solvent. The ultraviolet–visible spectrum has shown the occurrence of an intermolecular charge transfer between polysilane and the metal complex. Photoluminescence studies have revealed an interesting dual emission profile of nanocomposite. The origin of this phenomenon has been evidenced by molecular modeling and simulation of the electronic transitions. The modeling results have unveiled a new low‐lying excited state due to intermolecular interactions. The thin films of nanocomposites have been drop‐casted from solutions. The obtained films have been studied by Transmission Electron Microscopy (TEM)‐Scanning Transmission Electron Microscopy (STEM)‐Energy Dispersive X‐ray analysis (EDX) to gain information on the film‐forming capacity and surface morphology. The results have revealed a high potential of such materials for fluorescence sensing applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoinduced Electron‐Transfer Processes in Fullerene‐Based Donor–Acceptor Systems

Photoinduced electron‐transfer processes in fullerene‐based donor–acceptor dyads (D? B? A) in homogeneous and cluster systems are summarized. Stabilization of charge has been achieved through the use of fullerene substituted‐aniline/heteroaromatic dyads with tunable ionization potentials and also by using fullerene clusters. The rate constants for charge separation (k_CS) and charge recombination (k_CR) in fullerene substituted‐aniline/heteroaromatic dyads show that forward electron transfer falls in the normal region of the Marcus curve and the back electron transfer in the inverted region of the Marcus parabola. Clustering of fullerene‐based dyads assists in effective delocalization of the separated charge and thereby slows down the back electron transfer in these cases.     

Coexistence of Two Thermally Induced Intramolecular Electron Transfer Processes in a Series of Metal Complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)2] (M=Co,Fe, and Ni) bearing Non‐Innocent Catechol‐Based Ligands: A Combined Experimental and Theoretical Study

The different thermally induced intermolecular electron transfer (IET) processes that can take place in the series of complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)₂], for which M=Co ( 2 ), Fe ( 3 ) and Ni( 4 ), and Cat‐N‐BQ and Cat‐N‐SQ denote the mononegative (Cat‐N‐BQ^?) or dinegative (Cat‐N‐SQ^2?) radical forms of the tridentate Schiff‐base ligand 3,5‐di‐tert‐butyl‐1,2‐quinone‐1‐(2‐hydroxy‐3,5‐di‐tert‐butylphenyl)imine, have been studied by variable‐temperature UV/Vis and NMR spectroscopies. Depending on the metal ion, rather different behaviors are observed. Complex 2 has been found to be one of the few examples so far reported to exhibit the coexistence of two thermally induced electron transfer processes, ligand‐to‐metal (IET^LM) and ligand‐to‐ligand (IET^LL). IET^LL was only found to take place in complex 3 , and no IET was observed for complex 4 . Such experimental studies have been combined with ab initio wavefunction‐based CASSCF/CASPT2 calculations. Such a strategy allows one to solicit selectively the speculated orbitals and to access the ground states and excited‐spin states, as well as charge‐transfer states giving additional information on the different IET processes.     

Structurally characterized dinuclear zinc(II) bis(salamo)‐type tetraoxime complex possessing square pyramidal and trigonal bipyramidal geometries

A novel dinuclear Zn(II) complex with the chemical formula [Zn₂(L)(OCH₃)] has been synthesized by a bis(salamo)‐type tetraoxime ligand based on 3‐bromo‐5‐chlorosalicylicaldehyde, and characterized by elemental analyses, IR, UV–vis, and fluorescent spectra, and single‐crystal X‐ray diffraction analysis. All the Zn(II) atoms are pentacoordinated by N₂O₂ donor atoms from the (L)³⁻ unit and one oxygen atom from one μ₂‐methoxyl group. The Zn(II) (Zn1 and Zn4) atoms have distorted square pyramidal geometries (τ₁ = 0.458, τ₄ = 0.388), whereas the Zn2 and Zn3 atoms adopt trigonal bipyramidal (τ₂ = 0.675, τ₃ = 0.550) geometries. The Zn(II) complex is self‐assembled by intermolecular C H···O interactions to form an infinite three‐dimensional supramolecular structure. Interestingly, the intermolecular C H···π interactions in the Zn(II) complex is involved not in the formation of three‐dimensional structures but rather in the formation of the 0D dimer structure. Meanwhile, the optical properties of the Zn(II) complex were also measured and are discussed.     

Theoretical study of the electronic structure of LiX and NaX (X = Rb,Cs) molecules

Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels have been computed for the lowest electronic states of alkali dimers LiX and NaX (X = Rb, Cs). Calculations have been carried with the use of an ab initio approach with core‐potential potentials and full‐valence configuration. Thus, these systems are treated as two‐electron systems. A good agreement is obtained for some lowest states of the molecules studied with available theoretical works. The existence of numerous avoided crossings between electronic states for ¹Σ symmetries is related to the charge‐transfer process in each molecule between its two ionic systems (Li⁺X^?, Li^?X⁺) and (Na⁺X^?, Na^?X⁺). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Coordinative Interactions between Porphyrins and C60, La@C82, and La2@C80

For the first time, a C₆₀ derivative ( 1 ) and two different lanthanum metallofullerene derivatives, La@C₈₂Py ( 2 ) and La₂@C₈₀Py ( 3 ), that feature a pyridyl group as a coordination site for transition‐metal ions have been synthesized and integrated as electron acceptors into coordinative electron‐donor/electron‐acceptor hybrids. Zinc tetraphenylporphyrin ( ZnP ) served as an excited‐state electron donor in this respect. Our investigations, by means of steady‐state and time‐resolved photophysical techniques found that electron transfer governs the excited‐state deactivation in all of these systems, namely 1/ZnP , 2/ZnP , and 3/ZnP , whereas, in the ground state, notable electronic interactions are lacking. Variation of the electron‐accepting fullerene or metallofullerene moieties provides the incentive for fine‐tuning the binding constants, the charge‐separation kinetics, and the charge‐recombination kinetics. To this end, the binding constants, which ranged from log K_assoc=3.94–4.38, are dominated by axial coordination, with minor contributions from the orbital overlap of the curved and planar π systems. The charge‐separation and charge‐recombination kinetics, which are in the order of 10¹⁰ and 10⁸ s^?1, relate to the reduction potential of the fullerene and metallofullerenes, respectively.     

Rhenium(I) Polypyridine Diamine Complexes as Intracellular Phosphorogenic Sensors: Synthesis,Characterization, Emissive Behavior,Biological Properties,and Nitric Oxide Sensing

We report the development of a series of rhenium(I) polypyridine complexes appended with an electron‐rich diaminoaromatic moiety as phosphorogenic sensors for nitric oxide (NO). The diamine complexes [Re(N^N)(CO)₃(py‐DA)][PF₆] (py‐DA=3‐(N‐(2‐amino‐5‐methoxyphenyl)aminomethyl)pyridine; N^N=1,10‐phenanthroline (phen) ( 1 a ), 3,4,7,8‐tetramethyl‐1,10‐phenanthroline (Me₄‐phen) ( 2 a ), 4,7‐diphenyl‐1,10‐phenanthroline (Ph₂‐phen) ( 3 a )) have been synthesized and characterized. In contrast to common rhenium(I) diimines, these diamine complexes were very weakly emissive due to quenching of the triplet metal‐to‐ligand charge‐transfer (³MLCT) emission by the diaminoaromatic moiety through photoinduced electron transfer (PET). Upon treatment with NO, the complexes were converted into the triazole derivatives [Re(N^N)(CO)₃(py‐triazole)][PF₆] (py‐triazole=3‐((6‐methoxybenzotriazol‐1‐yl)methyl)pyridine; N^N=phen ( 1 b ), Me₄‐phen ( 2 b ), Ph₂‐phen ( 3 b )), resulting in significant emission enhancement (I/I₀≈60). The diamine complexes exhibited high reaction selectivity to NO, and their emission intensity was found to be independent on pH. Also, these complexes were effectively internalized by HeLa cells and RAW264.7 macrophages with negligible cytotoxicity. Additionally, the use of complex 3 a as an intracellular phosphorogenic sensor for NO has been demonstrated.     

Synthesis and crystal structure of a novel prochiral ketoimine: (E)‐acetophenone O‐diphenylphosphoryl oxime

A novel activated prochiral ketoimine, (E)‐acetophenone O‐diphenylphosphoryl oxime, C₂₀H₁₈NO₂P, with an electron‐withdrawing substituent on the imine N atom similar to other prochiral ketoimines, has been synthesized and the X‐ray crystal stucture determined. The molecules pack together in the solid state via weak intermolecular C—H...O interactions and both face‐to‐face and edge‐to‐face π‐stacking interactions.     

Fullerene Derivatives Functionalized with Diethylamino‐Substituted Conjugated Oligomers: Synthesis and Photoinduced Electron Transfer

Diethylamino‐substituted oligophenylenevinylene (OPV) building blocks have been prepared and used for the synthesis of two [60]fullerene–OPV dyads, F‐D1 and F‐D2 , which exhibit different conjugation length of the OPV fragments. The electrochemical properties of these acceptor–donor dyads have been studied by cyclic voltammetry. The first reduction is always assigned to the fullerene moiety and the first oxidation centered on the diethylaniline groups of the OPV rods, thus making these systems suitable candidates for photoinduced electron transfer. Both the OPV and the fullerene‐centered fluorescence bands are quenched in toluene and benzonitrile, which suggests the occurrence of photoinduced electron transfer from the amino‐substituted OPVs to the carbon sphere in the dyads in both solvents. By means of bimolecular quenching experiments, transient absorption spectral fingerprints of the radical cationic species are detected in the visible (670 nm) and near‐IR (1300–1500 nm) regions, along with the much weaker fullerene anion band at λ_max=1030 nm. Definitive evidence for photoinduced electron transfer in F‐D1 and F‐D2 comes from transient absorption measurements. A charge‐separated state is formed within 100 ps and decays in less than 5 ns.     

Trapped in Imidazole: How to Accumulate Multiple Photoelectrons on a Black‐Absorbing Ruthenium Complex

Ruthenium dyes incorporating a 4H‐imidazole chromophore as a ligand exhibit a spectrally broad absorption in the UV/Vis region. Furthermore, they show the ability to store two electrons within the 4H‐imidazole ligand. These features render them promising molecular systems, for example, as inter‐ or intramolecular electron relays. To optimize the structures with respect to their electron‐storage capability, it is crucial to understand the impact of structural changes accompanying photoinduced charge transfer in the electronic intermediates of multistep electron‐transfer processes. The photophysical properties of these (reactive) intermediates might impact the function of the molecular systems quite substantially. However, the spectroscopic study of short‐lived intermediates in stepwise multielectron‐transfer processes is experimentally challenging. To this end, this contribution reports on the electrochemical generation of anions identical to intermediate structures and their spectroscopic characterization by in situ resonance Raman and UV/Vis spectroelectrochemistry and computational methods. Thereby, an efficient two‐electron pathway to the 4H‐imidazole electron‐accepting ligand is identified.     

Synthesis and Characterization of Redox‐Active Charge‐Transfer Complexes with 2,3,5,6‐Tetracyanopyridine (TCNPy) for the Photogeneration of Pyridinium Radicals

The heteroaromatic polynitrile compound tetracyanopyridine (TCNPy) is introduced as a new electron acceptor for the formation of deeply colored charge‐transfer complexes. In MeCN, TCNPy is characterized by a quasireversible one‐electron‐reduction process at ?0.51 V (versus SCE). The tetracyanopyridine radical anion undergoes a secondary chemical reaction, which is assigned to a protonation step. TCNPy has been demonstrated to generate 1:1 complexes with various electron donors, including tetrathiafulvalene (TTF) and dihydroxybenzene derivatives, such as p‐hydroquinone and catechol. Visible‐ or NIR‐light‐induced excitation of the intense charge‐transfer bands of these compounds leads to a direct optical electron‐transfer process for the formation of the corresponding radical‐ion pairs. The presence of available electron donors that contain protic groups in close proximity to the TCNPy acceptor site opens up a new strategy for the photocontrolled generation of pyridinium radicals in a stepwise proton‐coupled electron‐transfer (PCET) sequence.     

Theoretical study of the interaction of fluorinated dimethyl ethers and the ClF and HF molecules. Comparison between halogen and hydrogen bonds

A theoretical study of the halogen‐bonded complexes formed between fluorinated dimethyl ethers (n_F = 0–4) and ClF is carried out using the wB97XD method combined with the 6‐311++G(d,p) basis set. The properties of the complexes are compared with the corresponding properties of the hydrogen‐bonded complexes formed between the same electron donors and HF. The optimized geometries, the interaction energies, relevant natural bonding orbital characteristics along with some vibrational data are calculated. The analyzed properties also include the symmetry adapted perturbation theory decomposition of the energies along with the atoms‐in molecule analysis. For both the halogen and hydrogen bonds, the interaction energies are ruled by the intermolecular hyperconjugation energies. In contrast, the correlations between the binding energies and the basic properties of the ethers or the charge transfer are different for the halogen and hydrogen bonds. The applicability of the Bent's rule to these systems is discussed. © 2016 Wiley Periodicals, Inc.     

Charge redistribution effect on the properties of charge transfer complexes HnR⋅XY and HnR⋅X2 (X,Y = F,Cl, Br,I; R = O,S, N,P)

Systematic studies on structures, energies, charge transfer, dipole moments, and ionic character of a series of weakly bonded charge transfer (CT) complexes (D⋅AB, D = H₂O, H₂S, NH₃, PH₃, AB = F₂, Cl₂, Br₂, I₂, BrCl, IBr, ClF, ICl, BrF, IF) have been carried out by the hybrid Hartree–Fock density functional theory (HF‐DFT) method, where those results are validated by available experimental and theoretical investigations. Employing the Hohenberg–Kohn theorem, the property of a multicomponent system is formulated with contributions from both component properties and the charge redistribution (CR) effect, which describes the electronic coupling between components. For any property of a multicomponent system, provided that the intercomponent coupling is weak enough, the first‐order approximation can be applied, which yields a linear correlation of the component contribution to the CR effect. In fact, this kind of linear relationship can be evidenced by all the studied properties including the geometry, energy, charge transfer, dipole moment, and ionic character of all 40 complexes. This approximation quantitatively describes the relative contribution of the components to a given property, which shows the same tendency in a series of complexes. Based on the investigations of the CT effect on the intermolecular bond energy and the total dipole moment, it has been found that the principal bonding character of the title complexes was ascertained to be ionic with the exception of the F₂ complexes, which agrees well with the calculated ionic character. The CT effect, though small in a quantitative aspect, is directly connected to various kinds of system properties. The effectiveness and consistency of the present type of calculations in multicomponent systems may allow their wider applications in the study of intermolecular interactions. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 327–338, 2001     

Synthesis of New Ruthenium（Ⅱ）Bipyridyl Complexes and Studies on Their Photophysical and Photoelectrochemical Properties

Two new mixed-ligand ruthenium(Ⅱ） complexes,Ru(dcbpy)-(LL)NCS)2[where dcbpy=4,4‘-dicarboxyl-2,2‘‘-bipyridine,LL=4,4‘-bis(N-methyl-anilinomethyl)-2,2‘‘-bipyridine(2)],were synthesized,and the tphotophysical properties of these complexes were studied.The metal-to-ligand charge transfer (MLCT) transitions of these complexes exhibited solvatochromic effect due to the existence of NCS ligands.The MLCT energies also strongly depend on the pH values of the solutions because of protonation and deprotonation of the carboxyl groups.The pKa values of the ground state,4.0 for 1 and 3.8 for 2,were obtained from the titration curves.The photoelectrochemical properties of 1 and 2 as sensitizers in sandwich-type solar cells have been studied.Complex 1 exhibited better photoelectrochemical behavior than complex 2 as expected.It was proved that the design of mixed-ligand complex by introducing electron donating group in one of the ligands should be a promising approach.     

Effect on Charge Transfer and Charge Recombination by Insertion of a Naphthalene‐Based Bridge in Molecular Dyads Based on Borondipyrromethene (Bodipy)

The photophysical properties of two related dyads based on a N,N‐dimethylaniline donor coupled to a fully‐alkylated boron dipyrromethene (Bodipy) acceptor are described. In one dyad, BD1 , the donor unit is attached directly to the Bodipy group, whereas in the second dyad, BD2 , a naphthalene spacer separates the two units. Cyclic voltammograms recorded for the two dyads in deoxygenated MeCN containing a background electrolyte are consistent with the reversible one‐electron oxidation of the N,N‐dimethylaniline group and the reversible one‐electron reduction of the Bodipy nucleus. There is a reasonable driving force (ΔG_CT) for photoinduced charge transfer from the N,N‐dimethylaniline to the Bodipy segment in MeCN. The charge‐transfer state is formed for BD1 extremely fast (1.5 ps), but decays over 140 ps to partially restore the ground state. On the other hand, the charge‐transfer state for BD2 is formed more slowly, but it decays extremely rapidly. Charge recombination for both dyads leads to a partial triplet formation on the Bodipy group. The naphthalene spacer group is extremely efficient at promoting back electron transfer.     

Experimental and theoretical investigation on adsorption and corrosion inhibition properties of imidazopyridine derivatives on mild steel in hydrochloric acid solution

Imidazopyridine derivatives, namely 4‐methoxy‐N‐((2‐(4‐methoxyphenyl)H‐imidazo[1,2‐a]pyridin‐3‐yl)methylene)benzenamine (MMPIPB) and 4‐chloro‐N‐((2‐(4‐methoxyphenyl)H‐imidazo[1,2‐a]pyridin‐3yl)methylene)benzenamine (CMPIPB), were investigated as inhibitors for mild steel corrosion in 15% HCl solution using the weight loss and electrochemical techniques. According to electrochemical impedance spectroscopy studies, MMPIPB and CMPIPB show corrosion inhibition efficiency of 84.8 and 77.2% at 10‐ppm concentration and 98.1 and 94.8% at 80‐ppm concentration, respectively at 303 K. The corrosion inhibition efficiency of both inhibitors increased with increasing inhibitor concentration and decreased with increasing temperature. The adsorption of both inhibitor molecules on the surface of mild steel obeys Langmuir adsorption isotherm. Polarization studies showed that both studied inhibitors were of mixed type in nature. Electrochemical impedance spectroscopy studies showed that for both inhibitors, the value of charge transfer resistance increased and double‐layer capacitance decreased on increasing the concentration of inhibitors. Scanning electron microscopy, energy‐dispersive X‐ray spectroscopy (EDX), and atomic force microscopy were performed for surface study. The density functional theory was employed for theoretical calculations. Copyright © 2014 John Wiley & Sons, Ltd.     

Meso-5，10，15，20-四-（对-甲氧基苯基）卟啉稀土氯化物的合成与表征

meso-Tetrakis-（p-methoxyphenyl）porphyrin rare earth chlorides, Ln（TMOPP）Cl （Ln： Dy, Ho, Tm, Yb, Lu and H2TMOPP： tetrakis-（p-methoxyphenyl）porphyrin）, were synthesized and characterized. Their composition, structure and properties were studied by elemental analyses, ultra-violet visible spectra, infrared spectra, luminescence spectra, molar conductances and thermal analysis. The four nitrogen atoms of the porphyrin are bonded to a central rare earth ion with four coordination numbers. The lanthanide ion lies above the porphyrin molecular plane and chloride ion is outside boundary of the coordination compound. Complexes are stable below 200℃ and do not contain small molecules （water or solvent）. Ultra-violet visible and infrared spectra were recorded and some of spectral bands were assigned. Surface photovoltaic spectroscopy （SPS） and electric-field induced surface photovoltaic spectroscopy （EFISPS） were measured. The spectral bands were assigned. The photovoltaic response is similar to the UV-visible absorption spectrum, therefore corresponding to analogous electron transition process.     

Visible Light Driven Copper(I) Catalyzed Oxyamination of Electron Deficient Alkenes†

A visible light driven Cu(I)‐catalyzed intermolecular oxyamination of electron‐deficient olefins has been achieved by using O‐benzoylhydroxylamines as donors both for amine and oxygen. The transformation properties afford mild conditions and a wide substrate scope, providing access to ester derivatives of β‐amino alcohols with good yields and high regioselectivity.