Modelling the circularly and linearly polarised spectrum of [Ni(en)3]2+

The relative intensity and band shapes of the low energy spin-allowed transitions in the linearly polarised and circular dichroism spectrum of [Ni(en)(3)](2+) have been calculated using a time-dependent density functional theory approach. The effect of the trigonal ligand-field is minimal and no splitting of the bands is predicted by the simulations or observed experimentally. The 'd-d' transitions of the [Ni(en)(3)](2+) ion are electric dipole allowed but gain much of their intensity through Herzberg-Teller vibronic coupling. Its CD spectrum is dominated by the low energy band, which gains its rotatory strength through the magnetic dipole-allowed character of the parent octahedral transition and the electric dipole character due to the trigonal field. The simulation of the spectrum incorporates the contribution from all inducing vibrational modes with significant involvement of the {NiN(6)} unit. Vibrations which are centred on the chelate rings are not important in generating intensity, reflecting the localised d-d' character of the transitions. Simulated linearly polarised and circular dichroism spectra of such an open-shell system are presented for the first time and predict the essential elements of the experimental spectra.     

Spectroscopic properties and ligand field analysis of cis-diazido(1,4,8,11-tetraazacyclotetradecane)chromium(III) azide

The emission and excitation spectra of cis-[Cr(cyclam)(N3)2](N3) (cyclam = 1,4,8,11-tetraazacyclotetradecane) taken at 77 K are reported. The infrared and visible spectra at room temperature are also measured. The vibrational intervals due to the electronic ground state are extracted from the far-infrared and emission spectra. The ten electronic bands due to spin-allowed and spin-forbidden transitions are assigned. Using the observed transitions, a ligand field analysis has been performed to determine the bonding property of azido group in the chromium(III) complex. It is found that azide ligand has weak sigma- and pi-donor properties toward chromium(III) ion. The zero-phonon line in the excitation spectrum splits into two components by 249 cm(-1), and the large 2Eg splitting can be reproduced by the ligand field theory.     

Electronic and vibrational spectroscopy of cis-beta-[CrCl(2)(1,4,7,11-tetrazaundecane)chromium(III) perchlorate

The sharp-line absorption spectrum of cis-beta-[CrCl(2)(2,2,3-tet)]ClO(4) (2,2,3-tet: 1,4,7,11-tetraazaundecane) has been measured between 13,000 and 16,000 cm(-1) at 5K. The 77K emission, 298 K infrared and visible spectra have also been measured. The zero-phonon band in the highly resolved absorption spectrum splits into four components. The vibrational intervals of the electronic ground state were determined from the far-infrared and emission spectra. The 10 electronic bands due to spin-allowed and spin-forbidden transitions were assigned. Using the observed transitions, a ligand field analysis has been performed to probe the ligand field properties of coordinated atoms in the title chromium(III) complex. The X-ray crystal structure at low-temperature was determined to help in assigning the sharp-line electronic transitions.     

四(4,4',4'',4'''-N,N-二氨基)四苯乙烯光致发光与分子的构象效应

利用还原偶联方法合成出新化合物四(4,4',4',4''-N,N-二氨基)四苯乙烯（ TDETE）。通过测定该化合物在溶液、掺杂聚合物中及晶体粉末的稳态-瞬态荧光光 谱、荧光量子产率和辐射衰变速率常数等。讨论了分子的构象效应等因素对TDETE 光致发光行为的影响。在一定浓度下TDETE溶液存在着三个发光带,分别为全扭曲 构象分子（位于345nm附近的发光I带）、半扭曲构象分子（位于430nm附近的发光 II带）和激基缔合物（530发光III带）的辐射衰变所致。在聚合物（PMMA）中,一 方面由于分子单键的自由旋转扭曲受到遏制,表现为II带的辐射衰变速率常数(kf 值)增大、同时非辐射衰变速率常数knf值减小;另一方面,TDETE分子之间相互作 用得到加强而有利一缔合物形成,结果,使发光II带和III带合二为一出现强而宽 的发射峰,荧光量子产率从溶液中的0.055提高到0.855。此外,在PMM介制裁中观 测到TDETE分子聚集体在626nm处的发光带（IV）,数粉末态中聚集体IV带的强度骤 增,峰值波长红移至650nm。     

Charge-transfer-type fluorescence of 4-(1H-pyrrol-1-yl)benzonitrile (PBN) and N-phenylpyrrole (PP) in cryogenic matrixes: evidence for direct excitation of the CT band

The fluorescence spectrum of PBN in a neat argon matrix is excitation-wavelength-dependent: at short excitation wavelengths, it consists of dual emission assigned to a charge-transfer (CT) state and a much weaker band assigned to the locally excited (LE) state. The CT emission is broad and almost completely devoid of vibrational structure, whereas the LE band is characterized by vibrationally resolved emission. At long excitation wavelengths, only CT emission is observed, indicating that the CT state is populated directly by light absorption and not via the LE state. Comparison with jet-cooled spectra of the bare molecule allows the unambiguous assignment of the LE spectrum and the location of the 0,0 band. The matrix LE emission spectrum is blue-shifted with respect to that of the gas phase, showing that the dipole moment of the LE state is smaller than that of the ground state. The fluorescence spectrum of PBN in an argon matrix does not change appreciably when acetonitrile (AN) is added to the matrix, in contrast to the case of N-phenylpyrrol (PP) (Schweke, D.; Haas, Y. J. Phys. Chem. A 2003, 107, 9554), for which addition of AN results in the appearance of two well separated emission bands. The different photophysical behaviors of PP and PBN in an argon matrix (and in supersonic jets) are analyzed by a simple model that considers the restriction of large-amplitude motions in the matrix. The implications of these low-temperature studies for understanding the properties of these systems in liquid solution are discussed.     

Laser-induced fluorescence and pure rotational spectroscopy of the CH2CHS (vinylthio) radical

Laser-induced fluorescence (LIF) excitation spectra of the B-X (2)A(") electronic transition of the CH(2)CHS radical, which is the sulfur analog of the vinoxy (CH(2)CHO) radical, were observed under room temperature and jet-cooled conditions. The LIF excitation spectra show very poor vibronic structures, since the fluorescence quantum yields of the upper vibronic levels are too small to detect fluorescence, except for the vibrationless level in the B state. A dispersed fluorescence spectrum of jet-cooled CH(2)CHS from the vibrationless level of the B state was also observed, and vibrational frequencies in the X state were determined. Precise rotational and spin-rotation constants in the ground vibronic level of the radical were determined from pure rotational spectroscopy using a Fourier-transform microwave (FTMW) spectrometer and a FTMW-millimeter wave double-resonance technique [Y. Sumiyoshi et al., J. Chem. Phys. 123, 054324 (2005)]. The rotationally resolved LIF excitation spectrum for the vibronic origin band of the jet-cooled CH(2)CHS radical was analyzed using the ground state molecular constants determined from pure rotational spectroscopy. Determined molecular constants for the upper and lower electronic states agree well with results of ab initio calculations.     

Spectroscopic studies of the electronic and vibrational spectra of tetramethylammonium fluorochromate(VI)

The electronic and vibrational spectra of tetramethylammonium fluorochromate(VI) have been measured. The observed electronic transitions correlated simply and directly with those of CrO ₄ ²⁻ . The electronic spectrum shows a weak band at about 450 nm and the edge of a very strong, broad band which extends beyond 344 nm. The intervening band has been identified with o oxygen-to-chromium charge transfer. This band exhibits a partially resolved vibrational progression or vibronic coupling due to excitation of a symmetric stretching mode in the CrO₃ group. This vibronic coupling is analyzed completely due to spectral correlation and symmetry of transitions, the Duschinsky effect, vibronic-spin-orbit coupling, environmental effect, anharmonicity order, vibrational intervals, and electronic rearrangement. The text was submitted by the authors in English.     

Hydrogen-bond vibrations in the S(1)<-->S(0) spectra of a nucleobase pair analog: a mixed dimer between 2-pyridone and formamide

The vibronically resolved electronic spectra for S(1)<-->S(0) transitions of a mixed dimer between 2-pyridone (2PY) and formamide have been measured in a supersonic free jet expansion using laser-induced fluorescence spectroscopy. Quantum chemistry method at different levels of theory has been used to optimize the geometries of the dimer for the S(0) and S(1) electronic states and also to calculate the normal vibrational modes. Assignments for the vibronic bands observed in the dispersed fluorescence spectrum of the 0(0) (0) band have been suggested with the aid of the ground state frequencies calculated by density functional theoretical method. Spectral analysis reveals that electronic excitation causes extensive mixing of the low-frequency intermolecular vibrational modes of the dimer with some of the intramolecular modes of the 2PY moiety. This spectral behavior is consistent with the complete active space self-consistent field theoretical prediction that with respect to a number of geometrical parameters the dimer geometry in S(1) is significantly distorted from the geometry of the S(0) state.     

Laser-induced fluorescence spectroscopy of NC3S

In a discharged supersonic jet of acetonitrile and carbon disulfide, we have for the first time observed an electronic transition of the NC(3)S radical using laser-induced fluorescence (LIF) spectroscopy. A progression originating from the C-S stretching mode of the upper electronic state appears in the excitation spectrum. Each band of the progression has a polyad structure due to anharmonic resonances with even overtones of bending modes. Rotationally resolved spectra have been observed by high-resolution laser scans, and the electronic transition is assigned to A 2Pii-X 2Pii. For the vibronic origin band, the position and the effective rotational constant of the upper level have been determined to be 21 553.874(1) and 0.046 689(4) cm(-1), respectively. The dispersed fluorescence spectrum from the zero vibrational level of A 2Pi3/2 has also been observed; its vibrational structure is similar to that of the LIF excitation spectrum, showing a prominent C-S stretching progression with polyad structures. The vibrational frequencies of the C-S stretching mode in the ground and excited electronic states are determined to be 550 and 520 cm(-1), respectively. Fluorescence decay profiles have been measured for several vibronic levels of the A state.     

Ca3La3(BO3)5中Eu3+的光致发光

本文详细地研究了紫外光激发下,Ca_3La_3(BO_3)_5中Eu~(3+)的发光光谱和激发光谱与组成、结构的关系.发现Eu~(3+)在此基质中可能不止一个发光中心;Eu~(3+)自身浓度猝灭的机理为电四极-四极相互作用.     

A reduction of the high symmetry of C60 in a PMMA polymer film as revealed by electroabsorption spectra

The absorption band of C₆₀ and C₇₀ located at 331 nm and 380 nm, respectively, in a PMMA polymer film shows a strong electric field effect, and the observed electroabsorption spectra are simulated by a superposition of the absorption spectrum, its first and the second derivative spectra, suggesting that electric dipole moment and molecular polarizability change following excitation into these bands. The presence of the electric dipole moment implies that inversion center does not exist in a polymer film not only on C₇₀ but also on C₆₀ in the ground state or/and the excited state.     

Electronic spectrum of a photochromic diarylethene derivative in a supersonic free jet. Internal conversion from S2(1B) to S1(2A)

The fluorescence excitation and dispersed fluorescence spectra of the open-ring isomer of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene have been measured in a supersonic free jet. No vibronic structure has been observed in the excitation spectrum. The intensity of fluorescence gradually increases with the excitation energy in the 25,500–28,700 cm⁻¹ region, indicating that the geometry of the molecule substantially changes upon photoexcitation. The dispersed fluorescence spectrum is anomaly Stokes-shifted with respect to the excitation energy, suggesting that the S₂(1B) state is initially excited followed by rapid internal conversion from the S₂(1B) to S₁(2A) state. The fluorescence is due to the S₁(2A)–S₀(1A) transition. Density functional theory calculations at the B3LYP/6-31G^** level have been carried out to investigate stable conformations responsible for the observed spectra.     

Exciton energy transfer between optically forbidden states of molecular aggregates

3-ethyl-2-[3-(3-ethyl-2(3H)-benzoxazolylidene)-1-propenyl]benzoxazolium iodide (dye I) and pseudoisocyanine bromide are employed to form H aggregates as donors and J aggregates as acceptors. The energy of an H band of the H aggregates is higher than that of a J band of the J aggregates. It was confirmed that excitation of the H band does not emit fluorescence by comparison of excitation spectra of dye I H aggregates with that of dye I monomer. Absorption, fluorescence, and excitation spectra of spin-coated films of H aggregates mixed with various quantities of J aggregates have been observed. Excitation spectra probed at the J band are found to have a component of the H band. Fluorescence spectra originated from excitation of the H band are extracted and qualitatively analyzed. It is confirmed that excitation of the H band causes to emit fluorescence of a J band of the J aggregates. These phenomena show that exciton energy can transfer from the lowest energy in electronic states of the H aggregate, which state is optically forbidden, to electronic state of the J aggregate.     

Study of the Electronic Structure of Ni(eta(5)-C(5)H(5))(NO) by Variable-Photon-Energy Photoelectron Spectroscopy and Density Functional Calculations

Photoelectron spectra, with photon energies varying from 18 to 120 eV, have been measured for Ni(eta(5)-C(5)H(5))(NO). Relative partial photoelectron cross sections and branching ratios have been evaluated for the first three valence ionization bands. He I and He II photoelectron spectra have been remeasured for Ni(eta(5)-C(5)H(5))(NO) and Ni(eta(5)-C(5)H(4)CH(3))(NO). In the latter case, the fine structure on the first band differs from that in the previously published spectrum. Density functional calculations have been carried out to determine the ionization potentials of the lowest lying states of Ni(eta(5)-C(5)H(5))(NO) as well as the corresponding photoionization cross sections and the resulting branching ratios using the LCGTO-DF and LDKL-DF methods, respectively. Both experimental and theoretical investigations lead to an ion state ordering (2)E(1) < (2)E(2) approximately (2)A(1)< (2)E(1) and an assignment of (2)E(1) states to the first and third bands with the (2)A(1) and (2)E(2) states comprising the second band. This differs from the original assignment in the literature, where the (2)A(1) ionization was assigned to a high-energy shoulder on the first band. The separation of this shoulder from the main band maximum of 0.23 eV (1850 +/- 81 cm(-)(1)) suggests that it may be caused by excitation of the NO stretching vibration in the ion. The neutral molecule has a NO stretch of 1832 cm(-)(1); the calculated energies for the neutral molecule and the cation are 1845 and 1911 cm(-)(1), respectively. Agreement between calculated and experimental ionization energies and good matching of the theoretical and measured branching ratios support the new assignment of the photoelectron spectrum.     

Optical Stark spectroscopy of the 2(0)(6) Ã1A'-X̃1A' band of chloro-methylene, HCCl

The laser induced fluorescence spectra of the 2(0)(6)A?(1)A(')-X?(1)A(') band of a rotationally cold (<20 K) molecular beam sample of chloro-methylene, HCCl, has been recorded, field-free and in the presence of a static electric field. The field-free spectrum has been analyzed to produce an improved set of spectroscopic parameters for the A?(1)A(') (060) vibronic state. The magnitude of the a-component of the permanent electric dipole moment, μ(a), for the X?(1)A(') (000) vibronic state has been determined to be 0.501(1) D from the analysis of the observed electric field induced shifts. Comparisons with theoretical predictions and flouro-methylene, HCF, are presented.     

The electronic spectrum of Si3 I: triplet D(3h) system

We report the measurement of a jet-cooled electronic spectrum of the silicon trimer. Si(3) was produced in a pulsed discharge of silane in argon, and the excitation spectrum examined in the 18 000-20 800 cm(-1) region. A combination of resonant two-color two-photon ionization (R2C2PI) time-of-flight mass spectroscopy, laser-induced fluorescence/dispersed fluorescence, and equation-of-motion coupled-cluster calculations have been used to establish that the observed spectrum is dominated by the 1(3)A(1)" - a? (3)A(2)' transition of the D(3h) isomer. The spectrum has an origin transition at 18,600 ± 4 cm(-1) and a short progression in the symmetric stretch with a frequency of ～445 cm(-1), in good agreement with a predicted vertical transition energy of 2.34 eV for excitation to the 1(3)A(1)" state, which has a calculated symmetric stretching frequency of 480 cm(-1). In addition, a ～505 cm(-1) ground state vibrational frequency determined from sequence bands and dispersed fluorescence is in agreement with an earlier zero-electron kinetic energy study of the lowest D(3h) state and with theory. A weaker, overlapping band system with a ～360 cm(-1) progression, observed in the same mass channel (m/z = 84) by R2C2PI but under different discharge conditions, is thought to be due to transitions from the (more complicated) singlet C(2v) ground state ((1)A(1)) state of Si(3). Evidence of emission to this latter state in the triplet dispersed fluorescence spectra suggests extensive mixing in the excited triplet and singlet manifolds. Prospects for further spectroscopic characterization of the singlet system and direct measurement of the energy separation between the lowest singlet and triplet states are discussed.     

Influence of environment on the electronic structure of Cob(III)alamins: time-resolved absorption studies of the S(1) state spectrum and dynamics

Transient absorption spectroscopy has been used to elucidate the nature of the S1 intermediate state populated following excitation of cob(III)alamin (Cbl(III)) compounds. This state is sensitive both to axial ligation and to solvent polarity. The excited-state lifetime as a function of temperature and solvent environment is used to separate the dynamic and electrostatic influence of the solvent. Two distinct types of excited states are identified, both assigned to pi3d configurations. The spectra of both types of excited states are characterized by a red absorption band (ca. 600 nm) assigned to Co 3d --> 3d or Co 3d --> corrin pi* transitions and by visible absorption bands similar to the corrin pi-->pi* transitions observed for ground state Cbl(III) compounds. The excited state observed following excitation of nonalkyl Cbl(III) compounds has an excited-state spectrum characteristic of Cbl(III) molecules with a weakened bond to the axial ligand (Type I). A similar excited-state spectrum is observed for adenosylcobalamin (AdoCbl) in water and ethylene glycol. The excited-state spectrum of methyl, ethyl, and n-propylcobalamin is characteristic of a Cbl(III) species with a sigma-donating alkyl anion ligand (Type II). This Type II excited-state spectrum is also observed for AdoCbl bound to glutamate mutase. The results are discussed in the context of theoretical calculations of Cbl(III) species reported in the literature and highlight the need for additional calculations exploring the influence of the alkyl ligand on the electronic structure of cobalamins.     

Relaxation of photo-excitations in films of oligo- and poly-(para-phenylene vinylene) derivatives

The photo-luminescence from solid films of poly(para-phenylene vinylene) polymers and an oligomeric model system, consisting of seven repeat units, are investigated at low temperature (8 K) using time-resolved spectroscopic techniques. Results are compared to those for the materials in solution. In the case of the oligomer, the shape of the visible absorption band observed for the film is quite different from the band shape for the polymer in frozen solution and is characteristic of H-type aggregates. Theoretical models are presented describing the dependence of the band shape of absorption and emission spectra on intermolecular excited state interactions, electron-vibration coupling and disorder represented by distributions of the molecular excitation and intermolecular interaction energies. Using these models, it is concluded that intermolecular interactions in the film of the oligomer are strong (1400 cm⁻¹), and the disorder low, implying delocalization of the excitation over several molecules. In accordance with these models the fluorescence lifetime for the film (2 ns) is considerably longer than for isolated molecules in solution (0.45 ns). The emission spectra of the film, taken early after excitation, are consistent with delocalization of the excitation over several molecules. A time-dependent red shift of the fluorescence band is observed and interpreted in terms of migration of localized excitations between disorder induced trap sites, which exist in the low energy tail of the density of excited states. For the polymers, differences between the shape of the absorption bands of solid film and frozen solution are smaller than for the oligomer indicating that interchain interactions that are, on average, weaker than for the oligomer. For the polymer films, a time-dependent red shift of the emission is observed and fluorescence depolarization measurements provide direct evidence for migration of the photo-excitations between trap sites. For one polymer, a time dependent change in the band shape of the fluorescence after pulsed excitation is observed with the band shape of the long-lived emission being compatible with that expected for an excitation delocalized over at least two, nearly parallel aligned, chains. For a second polymer, the emission band shape and its time evolution indicate that the major part of the fluorescence originates from disorder induced luminescent sites. These results indicate that the spectroscopic properties of films of π-conjugated polymer critically depend on parameters such as density of defects and excited state interchain interaction energy.     

Study on the Physical and Dissociation Properties of Disulfur Dichloride under Electric Fields

Disulfur dichloride is a hazardous substance, which is irritating to the eyes. It is significant to study the physical and dissociation properties under external electric fields. The bond length, energy, dipole moment, orbital energy level distribution, infrared spectra and dissociation properties of disulfur dichloride molecule under different external fields are obtained by using the density functional theory at the B3LYP/6-311++G(d, p) basis set level. In addition, ultraviolet-visible absorption spectra of the molecule in different electric fields are studied with configuration interaction-single excitation(CIS)/6-311++G(d, p) method. According to the results, it has been found that as the electric field exerted along the positive direction of the z-axis increases, the two sulfur-chlorine(S-Cl) bond lengths become longer and tend to break, while the sulfur-sulfur(S-S) bond length becomes shorter and the energy gap decreases. The infrared spectrum and ultraviolet-visible absorption spectra both exhibit red shift under electric field. Moreover, by scanning the potential energy surface of disulfur dichloride about S-Cl bond, the dissociation barrier decreases with the increase of positive electric field. When the external electric field arrives at 0.040 atomic units, the barrier disappears, meaning the dissociation of disulfur dichloride. The present results offer an important reference to further study of disulfur dichloride.     

Raman Optical Activity (ROA) as a New Tool to Elucidate the Helical Structure of Poly(phenylacetylene)s

Poly(phenylacetylene)s are a family of helical polymers constituted by conjugated double bonds. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them good candidates to be studied by Raman optical activity (ROA). Four different well‐known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. Raman and ROA spectra were recorded and allowed to establish ROA‐spectrum/helical‐sense relationships: a left/right‐handed orientation of the polyene backbone (M_helix/P_helix) produces a triplet of positive/negative ROA bands. Raman and ROA spectra of each polymer exhibited the same profile, and the sign of the ROA spectrum was opposite to the lowest‐energy electronic circular dichroism (ECD) band, indicating a resonance effect. Resonance ROA appears then as an indicator of the helical sense of poly(phenylacetylene)s, especially for those with an extra Cotton band in the ECD spectrum, where a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignment.