A quantum-chemical study of photophysical properties of complex compounds

For complexes of Re(I), Ru(II), and Os(II) containing some derivatives of 2,2′-bipyridine, the Franck-Condon components of the probabilities of nonradiative transitions involving excited states resulting from metal-to-ligand charge transfer are calculated. Two versions of the theory are used: with account of all the normal accepting modes and in the approximation of a single vibration of an efficient acceptor. Data on vibrational frequencies and changes in the geometrical parameters of the ligands upon excitation are obtained from ab initio quantum-chemical calculations. The calculated and experimentally determined constants of nonradiative transitions were found to correlate well with each other. The proposed procedure allows one to predict the photophysical properties of coordination compounds.     

Ultrasound-assisted synthesis of 2,5-dimethyl-N-substituted pyrroles catalyzed by uranyl nitrate hexahydrate

An efficient synthesis of different novel 2,5-dimethyl-N-substituted pyrrole derivatives by the Paal-Knorr condensation has been accomplished using uranyl nitrate hexahydrate as catalyst under soft conditions and ultrasonic irradiation. The synthesized compounds were confirmed through spectral characterization using IR, (1)H NMR, (13)C NMR and mass spectra.     

In-situ optical spectroscopy and electronic properties of pyrrole sub-monolayers on Ga-rich GaAs(001)

We report on the characterization of sub-monolayers of pyrrole adsorbed on Ga-rich GaAs(001) surfaces. The interfaces were characterized by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and reflectance anisotropy spectroscopy (RAS) in a spectral range between 1.5 and 8 eV. The adsorption of pyrrole on Ga-rich GaAs(001) modifies the RAS spectrum of the clean GaAs surface significantly at the surface transitions at 2.2 and 3.5 eV indicating a chemisorption of the molecules. By the help of transients at these surface transitions during the adsorption process, we were able to prepare different molecular coverages from a sub-monolayer up to a complete molecular layer. The different coverages of pyrrole were imaged by STM and electronically characterized by STS. The measurements reveal that the adsorbed molecules electronically insulate the surface and indicate the formation of new interface states around −3.5 and +4.2 eV. The RAS measurements in the UV region show new anisotropies in the spectral range of the optical transitions of the adsorbed pyrrole molecules. Our measurements demonstrate the potential of optical and electronic spectroscopy methods for the characterization of atomically thin molecular layers on semiconductor surfaces allowing a direct access to the properties of single adsorbed molecules.     

Theoretical analysis on geometries and electronic structures of antiaromatic pentalene and its N‐substituted derivatives: monomer,oligomers and polymer

The antiaromatic compounds have received a great deal of attention for several decades because of their unusual electronic structures. The electronic structures and properties of antiaromatic pentalene and its six nitrogen heterocyclic derivatives were systematically studied by the density functional theory at the Becke, three‐parameter, Lee–Yang–Parr level with 6‐31G* basis set. The results indicated that all the monomers have stable singlet states and remarkable bond‐length alternations. From the dimer to polymer in those molecules, pentalene(P), cyclopenta[b]pyrrole(CPP), cyclopenta[d]imidazole(CPI), pyrrolo[2,3‐b]pyrrole(PP1) and pyrrolo[3,2‐d]imidazole(PI) are stable diradical structures; pyrrolo[3,2‐b]pyrrole (PP2) and imidazo[4,5‐d]imidazole(II) are stable singlet ground states. The electronic properties including bond length, bond‐length alternation, electron density at bond critical points, Wiberg bond index and nucleus‐independent chemical shift were analyzed. It was found that in diradical molecules the bond‐length alternations are diminished, the charge tends to equilibrate, the π‐electron delocalization and conjugation are strengthened. The electronic properties of singlet ground state molecules have nearly no variations from monomers to polymers. The band structure analysis shows that diradical structure molecules have small band gaps (<1.0 eV), wide bandwidth and small effective masses of holes and electrons which suggest that diradical structure molecules are very good candidates for conductive materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Intramolecular electron transfer and charge delocalization in bistable donor–acceptor systems based on perchlorotriphenylmethyl radicals linked to ferrocene and tetrathiafulvalene units

A comparative analysis of the physicochemical properties of different donor–acceptor dyads, based on a perchlorotriphenylmethyl radical acceptor subunit linked through a vinylene π‐bridge to ferrocene derivatives (1–3) or a tetrathiafulvalene (4) donor subunit, is presented. Intramolecular electron transfer and charge delocalization of these donor–acceptor dyads are discussed on the basis of data obtained in solution by cyclic voltammetry, UV–Vis near‐infrared, and electron spin resonance spectroscopies. Bistability in the crystalline phase is also discussed on the basis of the results provided by X‐ray diffraction analysis and temperature‐dependent Mössbauer spectra. Copyright © 2014 John Wiley & Sons, Ltd.     

共价键相联的卟啉—酞菁激发态性质——(Ⅰ)二元分子化合物光谱特性研究

本文系统研究了二元分子TTP—O—Pc和TTP—O—(CH_2)_5—O—Pc的吸收光谱,发射光谱和激发光谱,区分了两组发光谱带的来源, 证实了由TTP到Pc的能量转移,利用激光频域技术获得了电荷弛豫时闻分别是18.5和82ps。     

共价键相联的卟啉—酞菁激发态性质——(Ⅰ)二元分子化合物光谱特性研究

本文系统研究了二元分子TTP—O—Pc和TTP—O—(CH₂)₅—O—Pc的吸收光谱,发射光谱和激发光谱,区分了两组发光谱带的来源, 证实了由TTP到Pc的能量转移,利用激光频域技术获得了电荷弛豫时闻分别是18.5和82ps。     

Linear and non-linear optical properties of hetero-cyclic aromatic polymers

We investigated linear and non-linear optical properties of non-fused and fully fused hetero-cyclic thiophene, selenophene and pyrrole oligomers. We found that these oligomers show relatively better environmental stability in their fused form than non-fused geometry. Linear extrapolation of calculated energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in the polymer limit exhibits extremely good agreement with experimentally reported band gap for thiophene, selenophene and pyrrole oligomers in their non-fused form. The lowest singlet dipole allowed excited state was calculated using time-dependent density functional theory and extrapolated optical gap estimated were in good agreement with experimental observation. Static linear and first hyperpolarisabilities were also studied as a function of chain length for donor–acceptor substituted polymers. The (hyper)polarisabilities are increasing as a function of chain length in both forms although the non-fused pyrrole oligomers show slow variation. Our study on hyperpolarisability also shows that donor–acceptor substituted non-fused selenophene oligomers are most promising candidates to contribute significantly in non-linear photonics and all fully fused hetero-cyclic oligomers show strong NLO responses.     

Analysis of benzodiaza‐15‐crown‐5 ether derivative binding properties by potentiometric and optical methods

This research concerns the analysis of the binding properties of benzodiaza‐15‐crown‐5 ether derivatives towards different metal ions (Mg(II), Cd(II), Ni(II), Cu(II), Zn(II), Pb(II), Hg(II) and Ag(I)) in acetonitrile and water by potentiometric and optical methods. Benzodiaza‐15‐crown‐5 ether demonstrates high binding affinity towards Hg²⁺ (lg K₁₁ = 12.7), whereas the stability constants of complexes with other studied cations varied from 3 to 6 logarithmic units. Copyright © 2012 John Wiley & Sons, Ltd.     

尼古丁分子的能级结构和光谱计算

研究尼古丁分子的能级结构与光谱特征,对更好地了解尼古丁分子的毒性和药性有理论指导作用.基于密度泛函理论(DFT),本文利用Gaussian 09软件在B3LYP/6-311G(d,p)基组水平上对尼古丁分子进行结构优化,再采用含时密度泛函理论(TD-DFT)在乙醇溶剂中计算尼古丁分子的15个激发态.使用Multiwfn波谱分析软件对分子前线轨道进行计算,并绘制出分子的红外谱图和紫外谱图.通过前线轨道分析可知,尼古丁分子的亲核位点是吡啶环上的C3和N6、亲电位点是吡咯环上的N22.吡啶环上的C-H、N-H键面内伸缩振动峰主要集中在3049～3079 cm~(-1),吡咯环上的甲基、亚甲基的伸缩振动峰主要集中在2796～3005 cm~(-1),其中在2816 cm~(-1)处甲基上C-H键振动峰最为明显,占比43.3%;吡咯环与吡啶环的摆动峰主要集中在1027～1455 cm~(-1),吡啶环的面内振动峰主要集中在1008～1027 cm~(-1),在800 cm~(-1)以下吸收峰都为吡啶环的面外摆动峰.紫外光谱的最大吸收峰位于173.46571 nm处,主要是由基态S0跃迁到激发态S5、S6、S10、S11、S12、S13、S14形成的,其中基态S0跃迁到激发态S11的贡献最大,其余激发态跃迁振子强度小于0.03,为禁阻跃迁.     

Fluorescence and Laser Emission from Coumarin-Acridine Orange Mixtures

The sensitized fluorescence and laser emissions of dye mixtures; (I) coumarin 102 (donor) and acridine orange (acceptor) and (II) coumarin 47 (donor) and acridine orange (acceptor) with Hg-lamp and N₂ laser, have been measured as a function of dye concentration and of the pump power (N₂ laser). Acridine orange which does not lase by itself on excitation with N₂ laser, lases efficiently in the presence of 7-amino-coumarins via singlet-singlet energy transfer. Energy transfer rate constants and critical distances have been estimated from fluorescence intensity and lifetime measurements. The performance of energy transfer dye lasers (ETDLs) are discussed in terms of spectral characteristics of the dyes and their penetration depths.     

Infrared Spectra of Metal (II) Complexes of 1, 3, 4-Thiadiazole-2, 5-Dithiol, 5-Amino-L, 2, 4-Dithiazol-3-Thione and Their Acetyl Derivatives

An infrared spectral interpretation of the structure of fifteen solid complexes formed by Co(II), Cu(II), Cd(II), Hg(II), Pb(II) and Zn(II) with ligands 1, 3, 4-thiadiazole-2, 5-dithiol (bismuthiol), 5-amino-l, 2, 4-dithiazolin-3-thione (xanthane) and the 2-acetyl-l, 3, 4-thiadiazol-5-thione and 5-acetylamide-l, 2, 4-dithiazol-3-t)thione derivatives is performed. The coexistence of different tautomers of bismuthiol and xanthane in the solid state is proposed. The bismuthiol-metal complexes display a unique and similar polymeric structure involving one tautomer. The xanthane-metal complexation stabilizes the 1, 1-dithiolate-type polymeric species; complexation with Cd, Co and Hg metal ions also stabilizes polymers involving the perthiocyanic teutomer.     

Electron Transfer Studies of Ruthenium(II) Complexes with Biologically Important Phenolic Acids and Tyrosine

The ruthenium(II) complexes having 2,2′-bipyridine and phenanthroline derivatives are synthesized and characterized. The photophysical properties of these complexes at pH 12.5 are studied. The electron transfer reaction of biologically important phenolic acids and tyrosine are studied using absorption, emission and transient absorption spectral techniques. Semiclassical theory is applied to calculate the rate of electron transfer between ruthenium(II) complexes and biologically important phenolic acids.     

CT-Operated Bifunctional Fluorescent Probe Based on a Pretwisted Donor–Donor–Biphenyl

Taking into account the structural requirements for TICT-type sensor molecules, a general synthetic route to derive pH and cation-responsive pretwisted donor (D)–donor (D) biphenyls (b) equipped with donor receptors is developed and a first model compound containing a mono aza-15-crown-5 and a DMA receptor is synthesized, see Scheme 1. The spectroscopic properties of this new bifunctional D–D biphenyl are studied in the non-polar and polar solvents cyclohexane, acetonitrile, and methanol. Protonation as well as complexation studies are performed with the representative metal ions Na(I), K(I), Ca(II), Ag(I), Zn(II), Cd(II), Hg(II), and Pb(II) to reveal the potential of this molecule for communication of whether none, only one, or both binding sites are engaged in analyte coordination by spectroscopically distinguishable outputs. The results are compared to those obtained with closely related donor (D)–acceptor (A) substituted biphenyl-type sensor molecules and are discussed within the framework of neutral and ionic D – A biphenyls.     

Theoretical studies of the structural,electronic and optical properties of carbazole‐based compounds

Carbazole derivatives have drawn increasing attention recently in organic electronic device applications because of their particular optoelectronic properties. An in‐depth theoretical investigation was elaborated in this paper to reveal the molecular structures, optoelectronic properties, and the structure‐property relationships of different carbazole‐linked functional groups. The geometric and electronic structures in ground and the mobility for the hole and electron are both calculated by density functional theory method. The excited‐state geometries of these compounds were obtained through Single‐excitation Configuration Interaction method, and time‐dependent density functional theory calculation results described the absorption and emission spectra properties, respectively. Some conclusions are as follows: (1) enlarging the π‐conjugated area, the corresponding spectra red shifted markedly; (2) by introducing the electron‐donor such as carbazole, the spectra blue shifted slightly; (3) compared with compound 1, the spectra for these compounds are hardly influenced by introducing an electron‐acceptor or heterocyclic substitution. On all accounts, these compounds are interesting optoelectronic functional materials. On the basis of their structural modifiability, the arylamine derivatives substituted carbazole compounds have great potential in the applications of organic light‐emitting diodes, organic solar cells, and sensors. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative photophysical and energy transfer studies of C480:C535 binary dye mixture in solid and liquid environments

The spectral behaviour of the individual dyes (C480 and C535) is discussed. The absorption and fluorescence spectral profiles of the dyes, in solid and liquid environments, are identical. Dye doped polymer rods of donor dye (C480) without the acceptor dye (C535), acceptor dye (C535) without the donor dye (C480) and donor dye with acceptor dye at different acceptor concentrations are synthesized. Energy transfer technique is studied, in detail, using these rods. The results obtained are compared with their respective liquid mixtures. Optical gain of the acceptor dye with and without the donor dye is determined experimentally, in both solid and liquid media. The gain of the acceptor with donor increases and then decreases with increase in acceptor concentration. Both solid and liquid media show similar trends. But, the gain coefficient in the solid matrix is less than that in the liquid medium. The photobleaching of the dye doped polymer rod under nitrogen laser excitation is studied.     

EPR investigations of synthetic manganese complexes as bio-mimics of the water oxidation complex in photosystem II

Research in the Swedish Consortium for Artificial Photosynthesis aims to construct a supramolecular system containing synthetically connected D (electron donor), S (photosensitizer), and A (electron acceptor) compartments. These are intended to carry out catalytic water oxidation on the donor side and catalytic hydrogen formation on the acceptor side, driven by light energy absorbed by the photosensitizer. In this minireview, we focus our attention on our spectroscopic and electrochemical studies of a series of manganese complexes partially mimicking the water-oxidizing manganese complex in the natural photosystem II (PSII), using ruthenium(II) tris(bypyridine) as the photosensitizer. The manganese complexes we discuss fall in three categories: monomeric manganese systems covalently linked to the ruthenium(II) tris(bypyridine) center, dimeric manganese complexes that are not covalently connected to ruthenium(II) tris(bypyridine) and dimeric manganese complexes covalently bound to a ruthenium(II) tris(bypyridine) center via an amide bound. The review focuses on the use of electron paramagnetic resonance spectroscopy in the studies of our manganese compounds.     

Interaction of water-soluble CdTe quantum dots with octacarboxy metallophthalocyanines: A photophysical and photochemical study

Water-soluble CdTe quantum dots capped with l-cysteine (QD-CYS) were found to improve the photophysical and photochemical properties of octacarboxy metallophthalocyanine (MOCPc, M=Zn(II), Al(III)(OH), Ge(IV)(OH)₂ and Si(IV)(OH)₂) complexes. Increased diffusional interactions between the molecules and the ground-state molecular oxygen were established resulting from the increase in the triplet-state quantum yield and lifetimes of the MOCPcs in the presence of QD-CYS. Energy transfer occurred from QD-CYS to the MOCPcs upon excitation of QD-CYS. It was found that an efficient energy transfer process, which is not directly related to the amount of spectral overlap between the donor (QD-CYS) and the acceptor (MOCPc) can occur. Singlet oxygen via fluorescence resonance energy transfer (FRET) mechanism was produced in the QD-MPc mixture.     

Polymorphism of 4-Fluorophenylpyruvic Acid Studied by X-Ray Crystallography and Vibrational Spectroscopy

Two polymorphic forms (I and II) of 4-fluorophenylpyruvic acid (F-PPA) were obtained by crystallization from different solvents, showing a melting point at 163.2 and 171.0 °C. Crystal structures of polymorphs I and II were determined by X-ray crystallography. IR and Raman spectra of the two polymorphs were measured and the spectral characteristics were compared with those of phenylpyruvic acid. the two polymorphs show similar molecular and crystal structures to each other, except for the molecular geometries of the enol and the carboxylic acid moieties. Distinct IR spectral differences which result from the crystal field splitting were observed between the two polymorphs.     

The influence of the nature of the coordinated metal atom on the photoelectrochemical activity of thin films of tetrapyrrole compounds

The photopotentials and photocurrents of thin films of various metal derivatives of tetrapyrrole compounds (TPCs) were compared to determine the photoelectrochemical activity of organic TPC semiconductors. The high reliability and reproducibility of the results were provided by a small spread of the parameters of the pigmented electrodes studied, a large statistical sampling, and thorough selection of determining measurement conditions. The results obtained for the photoelectrochemical reduction of oxygen show that TPC complexes with transition metals are effective in dark catalysis, because the special structure of their d shells provides strong overlapping with acceptor orbitals and dark electron transfer with a change in the valence of metals. Covalent bonds with ligands and a high electron density on the central atom contribute to this effect. In complexes of constant-valence metals with ionic bonds, acceptor coordination and reduction likely occur on pyrrole rings. The effectiveness of photoreduction increases as the ionization potential of TPCs decreases and electron density on the periphery of molecules grows.