Analysis of charge-transfer absorption and emission spectra on an absolute scale: evaluation of free energies, matrix elements, and reorganization energies

The relationship between the absorption and emission spectra of the charge-transfer complexes formed between a series of methyl-substituted benzene donors with 1,2,4,5-tetracyanobenzene as acceptor in 1,2-dichloroethane was examined in detail. The association constants for charge-transfer complex formation and the emission quantum yields for these complexes were used to place the experimental absorption and emission spectra on absolute scales. The simultaneous analysis of these spectra is valid only when the Mulliken two-state model is justified. For several of the complexes included in this study the electron-transfer parameters, including the electronic coupling matrix elements, obtained from the analysis of the individual absorption and emission spectra are in close agreement. The simultaneous analysis of the combined absorption and emission spectra leads to a well-defined set of electron-transfer parameters for these complexes. In other complexes, where the two-state model does not apply because of the influence of localized excited states on the absorption spectrum, analysis of the absorption and emission spectra led to significantly different sets of electron-transfer parameters. It is demonstrated that the electronic coupling matrix elements are a very sensitive indicator of the influence of localized excited states on these spectra.     

四-α(β)-(4-吡啶氧基)酞菁锌的光物理性质研究

测定了新合成的α位取代和β位取代的四-(4-吡啶氧基)酞菁锌配合物的UV-Vis吸收光谱、荧光光谱及激发单重态寿命、纳秒瞬态吸收光谱与激发三重态寿命.在此基础上,与相关配合物进行了比较,探讨了取代基及其取代位置对酞菁锌配合物的吸收光谱、激发单重态寿命及激发三重态寿命的影响.     

Photophysics and nonlinear absorption of peripheral-substituted zinc phthalocyanines

The photophysical properties, such as the UV-vis absorption spectra, triplet transient difference absorption spectra, triplet excited-state extinction coefficients, quantum yields of the triplet excited state, and lifetimes of the triplet excited state, of 10 novel zinc phthalocyanine derivatives with mono- or tetraperipheral substituents have been systematically investigated in DMSO solution. All these complexes exhibit a wide optical window in the visible spectral range and display long triplet excited-state lifetimes (140-240 mus). It has been found that the complexes with tetrasubstituents at the alpha-positions exhibit a bathochromic shift in their UV-vis absorption spectra, fluorescence spectra, and triplet transient difference absorption spectra and have larger triplet excited-state absorption coefficients. The nonlinear absorption of these complexes has been investigated using the Z-scan technique. It is revealed that all complexes exhibit a strong reverse saturable absorption at 532 nm for nanosecond and picosecond laser pulses. The excited-state absorption cross sections were determined through a theoretical fitting of the experimental data using a five-band model. The complexes with tetrasubstituents at the alpha-positions exhibit larger ratios of triplet excited-state absorption to ground-state absorption cross sections (sigma T/sigma g) than the other complexes. In addition, the wavelength-dependent nonlinear absorption of these complexes was studied in the range of 470-550 nm with picosecond laser pulses. All complexes exhibit reverse saturable absorption in a broad visible spectral range for picosecond laser pulses. Finally, the nonlinear transmission behavior of these complexes for nanosecond laser pulses was demonstrated at 532 nm. All complexes, and especially the four alpha-tetrasubstituted complexes, exhibit stronger reverse saturable absorption than unsubstituted zinc phthalocyanines due to the larger ratio of their excited-state absorption cross sections to their respective ground-state absorption cross sections.     

THE DEVELOPMENT OF EXCITON MIGRATION ROUTES FOR PHYCOCYANIN 645 AND ALLOPHYCOCYANIN

Abstract— The origin of the comparatively complex absorption spectrum of the cryptomonad biliprotein, phycocyanin 645 from Chroomonas species, has been investigated by deconvolution of its absorption and CD spectra together with fluorescence polarization studies. The visible absorption and CD spectra were each deconvoluted into four components, three pure Gaussian and one Gaussian-Lorentzian chimera. The difference spectrum between the visible absorption spectra of partially renatured and partially dissociated protein and the fluorescence polarization spectrum are compared to these deconvolutions. All results are consistent with a previous proposal that band splitting from a pair of strongly-coupled dipoles contributes to the absorption and CD spectra of this biliprotein. A model for the flow of exciton migration through this protein is presented that incorporates these data [together with appropriate literature reports]. This exciton migration model together with one for the biliprotein, allophycocyanin, includes both strong and very weak coupling of dipoles. This combination of mechanisms has salient influence on the visible absorption spectra and the routes of exciton migration characteristic of these two proteins.     

Ultraviolet spectra of metal ions in 6M hydrochloric acid

Ultraviolet absorption spectra of 66 metal ions in aqueous 6M hydrochloric acid were recorded and the spectra of 36 metal ions that absorb appreciably are reported. The absorption of these metal ions is sufficient to permit their detection in liquid chromatography.     

Cyclic imides. XII(i). Absorption and fluorescence spectra of 3-benzamidophthalimides

The ultraviolet absorption, fluorescence, and infrared absorption spectra of fifteen 3-benz-amidophthalimides are described. In general, the nature or position of the substituents on the benzamide moiety has little effect on the ultraviolet absorption and fluorescence spectra of these, compounds. The absorption baud at 271 nm is more sensitive to substituent variations than the other two bands (at 227 nm and 341 nm), indicating this band is a composite of bands observed in the spectra of 3-aminophthalimide and the substituted benzamide. The fluorescence of 3-amino-phthalirnide and the 3-benzamidophthalimides is due to the same transitions. The infrared absorption wavenumbers for the amide and imide vibrations of the 3-benzamidophthalimides are characterized.     

Visible light absorption by various titanium dioxide specimens

A set of heat-induced and photoinduced absorption spectra of various compositions of Degussa P25 TiO2 and different polymers has been examined. The spectra are described as the sum of overlapping absorption bands (ABs) with maxima at 2.90 eV (427 nm, AB1), 2.55 eV (486 nm, AB2), and 2.05 eV (604 nm, AB3); the spectra correlate entirely with the experimentally observed absorption spectra after the reduction of TiO2. Absorption spectra of visible-light-active TiO2 photocatalysts reported recently in the literature have also been analyzed. Relatively narrow absorption spectra are very similar and independent of the method of photocatalyst preparation. The average absorption spectrum can be described reasonably well by the sum of the two absorption bands AB1 and AB2. It is argued that visible light activation of TiO2 specimens (anion-doped or otherwise) implicates defects associated with oxygen vacancies that give rise to color centers displaying these absorption bands and not to a narrowing of the original band gap of TiO2 (EBG approximately 3.2 eV, anatase) through mixing of dopant and oxygen states, as has been suggested recently in the literature.     

三硼酸锂晶体的红外光谱与化学键的研究

测定了三硼酸锂(LiB_3O_5)晶体和低温相偏硼酸钡(β-BaB_2O_4)晶体的红外吸收光谱,用量子化学方法对这两种晶体的化学键性质进行了研究。从而定性地解释了LiB_3O_5晶体复杂的红外吸收光谱特征,并给以初步指认。     

Electronic absorption spectrum of radiation-produced pentane and hexane radical cations in saturated chlorofluorocarbon and perfluorocarbon matrices at 77 K.

Pentane and hexane radical cations are produced by irradiation, stabilized in saturated chlorofluorocarbon and perfluorocarbon matrices at 77 K and studied by electronic spectrometry. Special emphasis is laid on the obtainment of pure spectra by suitable deconvolution techniques. Electronic absorption spectra of these cations consist of a broad structureless absorption band with maximum at respectively 400 nm (pentane) and 480 nm (hexane). The absorption is intrinsic and is not to a considerable extent affected by the matrix. It is due to transitions from fully-occupied orbitals to the half occupied molecular orbital where the unpaired electron resides. A comparison is made of the electronic absorption spectra with photodissociation spectra obtained by ICR techniques and with theoretical spectra obtained by a conformationally-averaged MINDO/3 approach that includes transition-moment weighting.     

Optical absorption of 1H-pyrazolo[3,4-b]quinoline and its derivatives

The results of experimental studies and quantum chemical simulations of the absorption spectra of 1H-pyrazolo[3,4-b]quinoline and its derivatives are presented. The quantum chemical calculations (semi-empirical AM1 and PM3 methods) show similarity in the absorption spectra of 1H-pyrazolo[3,4-b]quinoline and 1,3-dimethyl-1H-pyrazolo[3,4-b]quinoline which are characterized by five strong absorption bands in the spectral range 200-500 nm. A substitution of the methyl groups by at least one phenyl group causes the drastic changes of the absorption spectra mainly within the spectral range 240-370 nm. We attribute these differences to additional molecular double bonding segments C=C of the substituted phenyl groups, i.e. to pi --> pi* transitions. A comparison of measured and the calculated absorption spectra manifests quite satisfactory agreement for all compounds in the part regarding the spectral position of the first oscillator (absorption threshold). At the same time, the measured spectra demonstrate the considerable broadening practically of all absorption bands and even complete damping some of them in the case of phenyl derivatives. The experiments performed with highly and weakly polar organic solvents shows that the solvent effect on the absorption spectra is small. For this reason the discrepancies between the calculated and the measured spectra are attributed to electron-vibronic coupling as well as to rotational dynamics of phenyl rings.     

二价铜、镍EDTA络合物晶体的电子吸收光谱

络合物晶体的电子吸收光谱作为研究晶体的电子结构的基础内容,很早以前就得到人们注意,虽然对Cu~(2+)、Ni~(2+)等络合物电子光谱的能级的经验指认已是一项较为成熟的工作,但对吸收光谱的系统的理论计算和定量解释在以前的文献中尚不多见.近年来,我们对多种晶体的电子吸收光谱进行了定量的解释,结果表明理论计算值总是能很好地符合于实验测定值。一般说来,吸收峰位的波数误差在8%以内. 早在本世纪四十年代就奠定了乙二胺四乙酸(EDTA)在分析化学中的应用基础。     

UV absorption spectra of 1,1'-binaphtyle and 2,2'-binaphtyle molecules and their self-associations from the atom monopole-dipole interaction (AMDI) model

The Atom Monopole-Dipole interaction (AMDI) model is used for the first time in calculation of UV absorption spectra of 1,1'-binaphtyl and 2,2'-binaphtyl and their self-associations for the case of frequency-dependant atom polarisability with Lorentzian band shape. UV absorption spectra are obtained from a set of electronic normal modes. The variation of spectra with the conformation of these molecules concord with the results of the medium effect on the corresponding electronic transitions. The calculated auto-association spectra are qualitatively in good agreement with polycyclic aromatic hydrocarbon aggregations behaviour.     

Theoretical simulation of UV absorption spectra of carbazole and some homocyclic analogs

The UV absorption spectra structures of carbazole, fluorene and dibenzofurane are studied using the atom monopole-dipole interaction (AMDI) model and atomic dipolar polarisabilities and effective charge given by Fraga. The absorption spectra corresponding to these molecules and their self-associations are presented. The original obtained results are discussed and compared to previous works.     

Electronic absorption spectra of merocyanine forms of spiropyrans

A simple method is proposed for the measurement of the absorption spectra in the visible and UV regions of photocolored solutions of spiropyrans, formed by the action of constant lowintensity UV irradiation, and for the construction, on the basis of these data, of the absorption spectra of the merocyanine forms of spiropyrans. The absorption spectra of the merocyanine forms of two spiropyrans in various solvents are examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1534–1538, November, 1972.     

Luminescent,optical, magnetic and metamaterial behavior of cerium complexes

The complexes of cerium with nitrogen, oxygen and sulfur donor ligands were prepared by conventional method. These newly synthesized complexes were characterized by FTIR, UV–Vis, DART Mass, TGA, PXRD, SEM and TEM techniques. The magnetic studies were carried out by the vibrating sample magnetometer. The optical constants were measured by absorption and reflection spectra as a function of wavelength. The concentration dependence of refractive index and absorption was observed by the experimental method, which reveals that these parameters are affected by change in concentration. The optical band gap obtained from Tauc-plot indicates its probability to be a good semiconductor. The luminescence behavior of these cerium complexes was observed by the absorption and emission spectra and the emission life time was calculated by their life time spectra.     

Ultrafast selected energy x-ray absorption spectroscopy investigations of Ni and Zn species

The results of ultrafast selected energy x-ray absorption spectroscopy (USEXAS) investigations of Ni and Zn species are presented. The USEXAS measurements described here employed characteristic x-ray radiation of L(alpha) and L(beta) from an ultrafast laser-driven W x-ray target to probe the K absorption edges of Ni and Zn, respectively. Static x-ray absorption edge spectra of six Ni and Zn species in either solid or solution form were obtained. Simulations of near-edge x-ray absorption spectra of these Ni and Zn species were carried out with FEFF. The results of USEXAS measurements were in general agreement with the theoretically simulated spectra and those measured with synchrotron x-ray radiation.     

Unique hydrophobic interactions of pyrene in aqueous solution as effected by polyelectrolytes and surfactants

Pyrene substituents covalently bounded to polyelectrolytes show not only excited-state interactions but also unique ground-state interactions in aqueous solution. The pyrene moieties in pyrenesubstituted ionic molecules also show these interactions when aqueous solutions of these molecules are treated with polyelectrolytes or surfactants well below their critical micelle concentrations. These hydrophobic interactions are revealed by changes in absorption, fluorescence, and excitation spectra. The well-resolved vibrational bands in the absorption and excitation spectra of pyrene become somewhat diffuse, whereas monomer fluorescence is reduced and replaced by excimer fluorescence. The rationale for these results is that the pyrene moieties in these ionic solutions seek out hydrophobic locations on the polyelectrolytes or surfactants, where pyrene aggregation is responsible for these interactions and the corresponding changes in spectra.     

Beiträge zur Chemie der Pyrrolpigmente, 84. Mitt.: Darstellung und Lumineszenz bichromophorer 5-Aryl-dipyrrinderivate

Summary 1,3- and 1,4-Bis-dipyrrin-benzenes and their various zinc and difluoroboryl chelates are prepared. Their absorption and fluorescence spectra are compared with those of the corresponding mono-dipyrrin derivatives. The conformations of these compounds are analyzed using the ring current model and absorption spectra. Dipole-dipole type transfer of excitation energy is discussed to represent a main photophysical channel in these compounds.

     

Fine structure at the carbon 1s K edge in vapours of simple hydrocarbons

Electron yield spectra in the range of 280 ? ?ω ? 300 eV which basically resemble the absorption spectra, have been measured for gaseous methane, ethane, ethylene, benzene and acetylene using synchrotron radiation. The spectra being fairly simple compared to the valence shell absorption are characterized by weak maxima for energies below the ionization threshold for C 1s for methane and ethane whereas additional strong resonances are observed in the spectra from molecules containing π-electrons. The nature of these excitations is discussed on the basis of their term values using information from XPS-measurements.