Electronic and structural effects on the nonlinear optical behavior in push-pull TTF/tricarbonyl chromiun arene complexes

A novel D-pi-A system in which tetrathiafulvalene (TTF) and pi-extended TTFs as strong electron donors are covalently connected to a tricarbonyl (eta(6)-arene)chromium complex as the acceptor moiety through a systematically increased conjugated bridge of vinylene units (12a-c, 16a-c) have been synthesized by Wittig-Horner olefination reaction. The electronic spectra as well as the electrochemical data reveal a different behavior of TTF derivatives (12a-c) and of exTTF derivatives (16a-c). Cyclic voltammetry shows the influence of the tricarbonylchromium arene on the oxidation potentials in compounds 12a-c, and no remarkable effect is observed for exTTFs (16a-c). The nonlinear optical properties of 12a-c and 16a-c have been calculated by using the ab initio CPHF/6-31G//B3P86/6-31G model, and the time-dependent density functional theory (TD-DFT) method has been used for the calculation of the electronic transitions. The calculations reveal that an intraligand charge-transfer transition (ILCT) and the metal to ligand charge-transfer transition (MLCT) are responsible for the nonlinear response. In addition, the large angles formed by the ground-state dipole moment and the vectorial hyperpolarizability are responsible for the mubeta values determined experimentally by the EFISH technique.     

Photophysical and electrochemical characterisation of the interactions between components in neutral pi-associated

The electrochemical and photophysical properties of a variety of neutral pi-associated [2]catenanes have been explored by using cyclic voltammetry, absorption and luminescence spectrophotometry and the measurement of exited-state lifetimes. Several trends that could be correlated with interactions between the mechanically linked components of the structures were revealed from comparative study of catenane precursors, model compounds and the [2]catenanes themselves. Throughout, emphasis is placed on pair-wise comparisons between systems which differ in a single structural feature. Substitution in a catenane of a pyromellitic diimide unit by a naphthalene diimide yields more readily reduced derivatives, whose absorption spectra reveal charge transfer within the catenane to be a lower energy process of reduced intensity. Conversion of the butadiyne links within the diimide macrocycle of the catenanes to saturated chains results in an increase in both the energy and intensity of their charge-transfer bands; electrochemically these derivatives are all harder to reduce than the parent systems. Replacement of one of the electron-donating components of the catenanes with a less effective aromatic donor bearing a carboxy group also decreases the energy and intensity of the charge-transfer feature and is accompanied by a slightly more ready reduction. A sequence of reduction and translational events is proposed to explain the intriguing electrochemical behaviour of a catenane that contains one pyromellitic and one naphthalene diimide. For some systems the photophysical and electrochemical techniques, whilst exploring distinct physical phenomena, are shown to be in good agreement by comparison of shifts of electrochemical reduction waves with those of charge-transfer absorption features.     

Chemical approach to neutral–ionic valence instability,quantum phase transition,and relaxor ferroelectricity in organic charge-transfer complexes

Neutral–ionic (NI) phase transition is a reversible switching of organic charge-transfer complexes between distinct valence states by external stimuli. This phase transformation in the low-dimensional system is demonstrated to provide a variety of novel dielectric, structural, and electronic properties. Importantly, ionization of the electron donor–acceptor pairs is usually accompanied by a ferroelectric or antiferroelectric order of the molecular lattice, leading to huge dielectric response near the transition point. Although these characteristics are potentially useful for future electronic and optical applications, the thermally accessible NI transition (TINIT) is still an extremely rare case. The TINIT compounds including some new materials are overviewed in order to provide convenient guides to their design and experimental identifications. The phase transition and dielectric properties can be closely controlled in various ways depending on chemical and physical modifications of the crystals. Among them, a quantum phase transition and relaxor ferroelectricity, both of which are currently attracting subjects from both scientific and practical perspectives, are highlighted as the first achievements in organic charge-transfer complexes.     

齐聚苯胺修饰的三联吡啶铁配合物的合成及其光谱和电化学性质

合成了一系列齐聚苯胺修饰的三联吡啶铁配合物,研究了齐聚苯胺链长、不同取代基等对配合物光谱性质和氧化还原性质的影响。 结果表明,相对于配合物[Fe(TPY)₂]²⁺(TPY:三联吡啶),供电子齐聚苯胺单元的引入,使得修饰基团与配合物中心核[Fe(TPY)₂]²⁺之间形成了强的D-A体系,导致配合物¹MLCT吸收波长显著红移至594 nm,且摩尔吸光系数增加近5倍。 配合物同时具有基于金属中心、三联吡啶配体和齐聚苯胺单元的多个氧化还原过程,强拉电子取代基使齐聚苯胺单元氧化还原峰简并且峰电势明显正移,而正丁基取代基对氧化还原峰电势的影响较小。     

Photophysical and electrochemical properties of 1,7-diaryl-substituted perylene diimides

Substituent effects on the photophysical and electrochemical properties of 1,7-diaryl-substituted perylene diimides (1,7-Ar(2)PDIs) have been carefully explored. Progressive red-shifts of the absorption and emission maxima were observed when the electron-donating ability of these substituents was increased. Linear Hammett correlations of 1/lambda(max) versus sigma(+) were observed in both spectral analyses. The positive slopes of the Hammett plots suggested that the electronic transitions carry certain amounts of photoinduced intramolecular charge-transfer (PICT) character from the aryl substituents to the perylene diimide core which leads to the reduction of the electron density on the substituents. The substituent electronic effects originated mainly from the perturbation of the core PDI HOMO energy level by the substituents. This conclusion was supported by PM3 analyses and confirmed by cyclic voltammetry experiments. More interestingly, the Ph(2)NC(6)H(4)-substituted PDI, 4i, showed an unusual dual-band absorption that spans from 450 to 750 nm. We tentatively assigned these two bands as the charge-transfer band and the PDI core absorption, respectively.     

A strategy for improving the room-temperature luminescence properties of Ru(II) complexes with tridentate ligands

Several ruthenium(II) complexes with new tridentate polypyridine ligands have been prepared, and their photophysical properties have been studied. The new tridentate ligands are tpy-modified systems (tpy = 2,2':6',2' '-terpyridine) in which aromatic substituents designed to be coplanar with the tpy moiety are introduced, with the aim of enhancing delocalization in the acceptor ligand of the potentially luminescent metal-to-ligand charge-transfer (MLCT) state and increasing the MLCT-MC energy gap (MC = metal-centered excited state). Indeed, the Ru(II) complexes obtained with this new family of tridentate ligands exhibit long-lived luminescence at room temperature (up to 200 ns). The enhanced luminescence properties of these complexes support this design strategy and are superior to those of the model Ru(tpy)22+ compound and compare favorably with those of the best Ru(II) complexes with tridentate ligands reported so far.     

Luminescent alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine-type ligands with ready tunability of the nature of the emissive states by solvent and electronic property modulation

A new class of luminescent alkynylplatinum(II) complexes of tridentate bis(N-alkylbenzimidazol-2'-yl)pyridines (bzimpy), [Pt(R,R'-bzimpy)(C[triple chemical bond]C-R')]X (X=PF(6), OTf), and one of their chloro precursor complexes, [Pt(R,R'-bzimpy)Cl]PF(6), have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X-ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand-based in nature with some mixing of the metal center-based contribution, whereas the two quasi-reversible reduction couples are mainly bzimpy-based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high-energy and intense absorption bands are assigned as the pi-pi* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low-energy and moderately intense absorptions are assigned to an admixture of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(R,R'-bzimpy)) and ligand-to-ligand charge-transfer (LLCT) (pi(C[triple chemical bond]C-R')-->pi*(R,R'-bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic-structured or structureless emission bands, originating from triplet metal-perturbed intraligand (IL) or an admixture of triplet metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1, and were ascribed to the formation of aggregate species through PtPt and pi-pi stacking interactions. DFT and time-dependent DFT (TD-DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.     

Synthesis, characterization, luminescence and nonlinear optical (NLO) properties of truxene-containing platinum(II) alkynyl complexes

A series of luminescent trinuclear platinum(II) alkynyl complexes containing dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene (truxene) as the core and aryl alkynyl ligands with different electronic properties at the periphery has been successfully synthesized and characterized. The electronic absorption, emission, nanosecond transient absorption and electrochemical properties of these complexes have been reported. These complexes showed long-lived emissions in degassed benzene solution at room temperature, and their emissions have been assigned to originate from triplet states of intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) character. The luminescent platinum(II) alkynyl complexes are found to show two-photon absorption (2PA) and two-photon induced luminescence (TPIL) properties, and their two-photon absorption cross-sections have been determined to be 6-51 GM upon excitation at 720 nm.     

水溶液中二氧化碳电还原技术的发展现状、挑战及对策

二氧化碳(CO₂)电化学还原利用CO₂生产低碳燃料,能够实现可再生能源存储同时降低温室气体排放对环境的负面影响,因而成为了近年里一个甚受瞩目的研究与开发热点. 尽管以往科学家关于催化剂活性、产物选择性以及反应机理的基础研究已做了广泛的报道,但对催化稳定性和电化学反应器系统的设计及实用性方面还未给予充分重视. 本文针对影响低温水溶液中二氧化碳电化学还原技术实用化的上述两个重要因素, 从技术应用需求角度出发,在概述发展现状基础上,总结归纳了主要存在的技术挑战,对未来研究方向提出了建议性对策.     

Copper-based metal-organic frameworks for electrochemical reduction of CO2

The electrochemical CO₂ reduction reaction (CO₂ER) is an emerging process that involves utilizing CO₂ to produce valuable chemicals and fuels by consuming excess electricity from renewable sources. Recently, Cu and Cu-based nanoparticles, as earth-abundant and economical metal sources, have been attracting significant interest. The chemical and physical properties of Cu-based nanoparticles are modified by different strategies, and CO₂ can be converted into multicarbon products. Among various Cu-based nanoparticles, Cu-based metal-organic frameworks (MOFs) are gaining increasing interest in the field of catalysis because of their textural, topological, and electrocatalytic properties. In this minireview, we summarized and highlighted the main achievements in the research on Cu-based MOFs and their advantages in the CO₂ER as electrocatalysts, supports, or precursors.     

New π-electron donors: Ethanediylidene-2,2′-bis(1,3-diselenole) and ethanediylidene-2-(1,3-dithiole)-2′-(1,3-diselenole)

This communication describes synthesis and electrochemical properties of new type of π-donors containing 1,3-diselenole ring, ethanediylidene-2,2′-bis(1,3-diselenole)(1a) and ethanediylidene-2-(1,3-dithiole)-2′-(1,3-diselenole)(2a). The conductivities of the charge-transfer complexes of these donors with tetracyanoquinodimethane (TCNQ) are also demonstrated.     

Spectral and photophysical properties of mono and dinuclear Pt(II) and Pd(II) complexes: An unusual emission behaviour

Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M₂(BPY)₂(THB)] where M = Pd(II) or Pt(II), N-N = 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,3′,4,4′-tetrahydroxy benzaldazine were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT) band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] where DHBA is the dianion of 3,4-dihydroxybenzoic acid and [Pt₂(BPY)₂(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature and a high-energy state at room temperature. Photophysics of these complexes is also discussed.     

Recent progress and design principles of nanocomposite solid electrolytes

The electrochemical performance of all-solid-state batteries is largely determined by the physicochemical properties of the solid electrolytes. However, none of a single-type solid electrolyte can meet all practical requirements for all-solid-state batteries, including high ionic conductivity, wide electrochemical window, stable interfacial chemistry, robust mechanical properties, and so on. The nanocomposite solid electrolytes have provided a facile solution to address the above challenges, and great achievements have been made in this field. This review briefly summarizes the recent development of the nanocomposite solid electrolytes, focusing on the fundamentals of ionic charge transfer and chemical evolutions at the heterointerface. With the discussion, we hope to shed light on the rational design of solid electrolytes toward the optimal operational performance of all-solid-state batteries.     

Recent Advances in Electropolymerized Conducting Polymers in Amperometric Biosensors

Conducting electroactive polymers (CPs) are materials discovered just over 20 years ago which have aroused considerable interest on account of their electronic conducting properties and unique chemical and biochemical properties. Consequently, they have numerous (bio)analytical and technological applications. CPs are easily synthesized and deposited onto the conductive surface of a given substrate from monomer solutions by electrochemical polymerization with precise electrochemical control of their formation rate and thickness. Coating electrodes with CPs under mild conditions opens up enormous possibilities for the immobilization of biomolecules and bioaffinity or biorecognizing reagents, the improvement of their electrocatalytic properties, rapid electron transfer and direct communication to produce a range of analytical signals and new analytical applications. Co-immobilization of other molecules (enzymatic co-factors or charge-transfer mediators) by entrapment within electropolymerized films or by covalent binding on these films permits straightforward fabrication of reagentless biosensors. The characteristics of CPs and their uses, mainly in amperometric biosensors, are reviewed. The most recent applications and lines of research related to CP films are summarized in the different sections of the paper, and probable future trends are discussed.     

Is Iron the New Ruthenium?

Ruthenium complexes with polypyridine ligands are very popular choices for applications in photophysics and photochemistry, for example, in lighting, sensing, solar cells, and photoredox catalysis. There is a long-standing interest in replacing ruthenium with iron because ruthenium is rare and expensive, whereas iron is comparatively abundant and cheap. However, it is very difficult to obtain iron complexes with an electronic structure similar to that of ruthenium(II) polypyridines. The latter typically have a long-lived excited state with pronounced charge-transfer character between the ruthenium metal and ligands. These metal-to-ligand charge-transfer (MLCT) excited states can be luminescent, with typical lifetimes in the range of 100 to 1000 ns, and the electrochemical properties are drastically altered during this time. These properties make ruthenium(II) polypyridine complexes so well suited for the abovementioned applications. In iron(II) complexes, the MLCT states can be deactivated extremely rapidly (ca. 50 fs) by energetically lower lying metal-centered excited states. Luminescence is then no longer emitted, and the MLCT lifetimes become much too short for most applications. Recently, there has been substantial progress on extending the lifetimes of MLCT states in iron(II) complexes, and the first examples of luminescent iron complexes have been reported. Interestingly, these are iron(III) complexes with a completely different electronic structure than that of commonly targeted iron(II) compounds, and this could mark the beginning of a paradigm change in research into photoactive earth-abundant metal complexes. After outlining some of the fundamental challenges, key strategies used so far to enhance the photophysical and photochemical properties of iron complexes are discussed and recent conceptual breakthroughs are highlighted in this invited Concept article.     

Synthesis,characterization, and DNA binding properties of a series of Ru,Pt mixed-metal complexes

A series of mixed-metal complexes coupling ruthenium light absorbers to platinum reactive metal sites through polyazine bridging ligands have been prepared of the form [(tpy)RuCl(BL)PtCl(2)](PF(6)) (BL = 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq), 2,3-bis(2-pyridyl)benzoquinoxaline (dpb); tpy = 2,2':6',2' '-terpyridine). These systems possess electron-rich Ru metal centers bound to five polyazine nitrogens and one chloride ligand. This leads to complexes with low-energy Ru --> BL charge-transfer bands that are tunable with BL variation occurring at 544, 632, and 682 nm for dpp, dpq, and dpb, respectively. This tuning of the charge-transfer energy results from a stabilization of the BL(pi) orbitals in this series as evidenced by the cathodic shift in the first reduction of these complexes occurring at -0.50, -0.32, and -0.20 V vs Ag/AgCl, for dpp, dpq, and dpb, respectively. The chlorides bound to the Pt(II) center are substitutionally labile giving these complexes the ability to covalently bind to DNA. All three title bimetallics, [(tpy)RuCl(BL)PtCl(2)](PF(6)), avidly bind double-stranded DNA with t(1/2) = 1-2 min, substantially reducing the migration of DNA through an agarose gel. Details of the synthetic methods, FAB MS data, spectroscopic and electrochemical properties, and DNA binding studies are presented.     

Solvent effects on charge-transfer intensities and heats of formation of chloranil complexes with aromatic hydrocarbons

The spectrophotometric and thermodynamic properties of the charge-transfer complexes of chloranil with aromatic hydrocarbons such as benzene, toluene, xylenes (o-, m- and p-) and mesitylene have been studied in n-heptane solvent to make a correlation between the charge-transfer intensities and the heats of formation of the complexes. The results disagree with Mulliken's prediction—the charge-transfer intensities decrease with increase of heats of formation. An attempt has been made to calculate the thermodynamic as well as spectrophotometric properties of these complexes free from the influence of chloranil—solvent interaction and the results thus obtained show a good correlation between the charge-transfer intensities and the heats of formation of the complexes.     

光助燃料电池的研究进展

化石燃料的大量开采和利用所导致的能源与环境问题是当今社会可持续发展必须面对的两大挑战. 燃料电池通过电化学反应将燃料中的化学能直接转化为电能, 是目前清洁高效的可再生能源转化装置. 光助燃料电池将光响应成分引入到燃料电池中, 可以实现光能/电能和化学能/电能的双重转化, 从而有效提高能源利用效率, 是未来能源转化装置的发展方向, 在实际应用方面具有重要意义和广阔前景. 本文对光助燃料电池进行了简要综述, 重点介绍了我们小组近些年来在该领域的相关研究进展, 总结了目前存在的一些问题, 并对其发展趋势进行了展望.     

Study of the Adsorption of Glutathione on a Gold Electrode by Using Electrochemical Quartz Crystal Impedance, Electrochemical Impedance Spectroscopy, and Cyclic Voltammetry

Adsorption of a biological peptide, glutathione, on a gold electrode was studied by using electrochemical quartz crystal impedance (EQCI), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The time courses of responses of piezoelectric and electrochemical impedance parameters were simultaneously obtained during the adsorption processes of the two forms of peptide, oxidized and reduced glutathione. It was found that the frequency curve due to the oxidized glutathione (GSSG) adsorption exhibited a character of a sum of two exponential functions. For reduced glutathione (GSH), the frequency adsorption curve could be expressed by a first-order reaction kinetic model and the corresponding kinetic parameters at different amounts of GSH were obtained. The heterogeneous charge-transfer rate constants of ferricyanide/ferrocyanide before and after the peptide adsorption were determined by CV and EIS methods, respectively. According to the simple equivalent electric network of the electrochemical interface, the electrochemical impedance parameters were also obtained. The results showed that the proposed method should be found in wider applications in interfacial biochemistry studies since these combined techniques have advantages in real time multidimensional information including electrochemical and electrochemical impedance parameters. Copyright 2000 Academic Press.     

New luminescent cyclometalated iridium(III) diimine complexes as biological labeling reagents

We report the synthesis, characterization, and photophysical and electrochemical properties of thirty luminescent cyclometalated iridium(III) diimine complexes [Ir(N-C)(2)(N-N)](PF(6)) (HN-C = 2-phenylpyridine, Hppy; 2-(4-methylphenyl)pyridine, Hmppy; 3-methyl-1-phenylpyrazole, Hmppz; 7,8-benzoquinoline, Hbzq; 2-phenylquinoline, Hpq; N-N = 4-amino-2,2'-bipyridine, bpy-NH(2); 4-isothiocyanato-2,2'-bipyridine, bpy-ITC; 4-iodoacetamido-2,2'-bipyridine, bpy-IAA; 5-amino-1,10-phenanthroline, phen-NH(2); 5-isothiocyanato-1,10-phenanthroline, phen-ITC; 5-iodoacetamido-1,10-phenanthroline, phen-IAA). The X-ray crystal structure of [Ir(mppz)(2)(bpy-NH(2))](PF(6)) has also been investigated. Upon irradiation, all the complexes display intense and long-lived luminescence under ambient conditions and in 77-K glass. On the basis of the photophysical and electrochemical data, the emission of most of these complexes is assigned to an excited state of predominantly triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir) --> pi(N-N)) character. In some cases, triplet intraligand ((3)IL) (pi --> pi)(N-N or N-C(-)) excited states have also been identified. In view of the specific reactivity of the isothiocyanate and iodoacetamide moieties toward the primary amine and sulfhydryl groups, respectively, we have labeled various biological molecules with a selection of these luminescent iridium(III) complexes. The photophysical properties of the luminescent conjugates have been investigated. In addition, a heterogeneous assay for digoxin has also been designed on the basis of the recognition of biotinylated anti-digoxin by avidin labeled with one of the luminescent iridium(III) complexes.