On the Anomalous Absorption Spectra of Amino- and Hydroxy-Substituted Anthracenes

It has been known for some time that the longest wavelength absorption band of anthracene arises from the transversely polarized ¹L_a ← ¹A absorptive transition (1). The angular momentum forbidden ¹L_b ← ¹A transition, which is invariably at least ten-fold weaker than the former transition in the acenes has been predicted, on theoretical grounds, to be submerged in the ¹L_a ← ¹A absorption envelope (2). That the ¹L_b ← ¹A transition of anthracene does not lie much higher in energy than the ¹L_a ← ¹A transition was demonstrated by Baba and Suzuki (3) who proved that although the long-wavelength absorption band of 1-anthrol originated from the ¹L_a ← ¹A absorption, as anticipated, the long-wavelength absorption bands of 2-anthrol and its conjugate anion originated from the admixture of charge-transfer from the β-hydroxy group into the longitudinally polarized ¹A ← ¹L_b transition of anthracene.     

Calculation and interpretation of the absorption and fluorescence spectra of indole in the isolated state and aqueous solution

We have calculated the vibronic absorption and fluorescence spectra of the first (¹ L _b ) and second (¹ L _a ) electronic transitions of indole in the isolated state and aqueous solution. The vibrational structure of the absorption and fluorescence spectra has been interpreted. The influence of the aqueous solution on the vibronic spectra has been shown.     

Electronic energy of the <Superscript>1</Superscript><Emphasis Type="Italic">L</Emphasis><Subscript>a</Subscript> level of supersonic jet-cooled indole

The dependence of the fluorescence polarization degree on frequency upon excitation into the first and second electronic bands of jet-cooled indole has been studied. A structured band consisting of a number of lines rather than a single line has been recorded in the spectral range of the electronic ¹A′-¹L_a-transition. The appearance of the lines is interpreted as the result of nonadiabatic vibronic interaction between the electronic ¹L_a-state and vibronicl states of the indole molecule ¹L_b-level. The energy of the unperturbed electronic ¹L_a-level and the orientation of dipole moments near the ¹A′-¹L_a-transition have been found. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 319–323, May–June, 2008.     

Interpretation of electronic spectra by configuration analysis: Absorption spectra of monosubstituted naphthalenes

The electronic absorption spectra of four monosubstituted naphthalenes, α-, β-naphthols, and α-, β-naphthylamines have been investigated by means of configuration analysis with particular attention to the dependence of spectra on the position of substitution and on the electron-donating power of the substituent. The results of molecular orbital calculations based on the Pariser-Parr-Pople method are analyzed in terms of locally excited states and intramolecular charge-transfer configurations. The characteristic changes in location and polarization of the L_b, L_a, and B_b bands caused by substitution at the α- or β-position are adequately explained by the analysis. Two strong absorption bands of α-substituted naphthalenes, which appear in place of the B_b band of naphthalene, are shown to result from a mixing of the $\text{B}{}_{\mathrm{3u}}{}^{\mathrm{+}}\text{(B}{}_{\mathrm{b}}\text{)}$ and $\text{A}{}_{\mathrm{g}}{}^{\mathrm{?}}$ states. The amino group exerts a great influence on the electronic structure of the parent molecule, so that the B_b band cannot be identified in the spectrum of β-naphthylamine.     

Assignments of visible absorption of s-tetrazine vapor

A detailed vibrational analysis of the 5515 Å absorption of s-tetrazine (tetra-azabenzene) vapor is attempted. More than 80% of the total intensity of the system can be accounted for by band assignments to a single allowed electronic transition, ¹B_3u-¹A_g. The only progression-forming vibration in absorption in ν_6a. Three progressions in ν′_6a account for all intense cold bands. Isotopic shifts of bands lead to convincing assignments of the two excited-state vibrations upon which ν_6a progressions are based, namely ν_6b and ν_8a. It is shown that in all probability the antisymmetric mode ν_6b is prominent because of vibrational (Fermi) resonance rather than because of vibronic interactions.     

Linear polarization studies of the high-resolution absorption spectrum of palladiumporphin

The results of linear polarization measurements on the vibronic bands in the S₁ ← S₀ absorption spectrum of palladiumporphin (PdP) are reported. The experiments have been performed at 1.2 K on single crystals of dilute solutions of PdP in n-octane, n-nonane, and n-decane. The symmetries of a number of bands are assigned. From a comparison of the results with those found for the free base porphin it is concluded that the crystal field has a relatively high effective symmetry and that the optical transition moments run through pairs of opposite nitrogen atoms. The manifestation in the polarized absorption spectra of different sites is discussed. It is finally shown that the 180-cm^?1 Jahn-Teller active vibration in zincporphin has b_1g symmetry.     

Vibronic coupling and intersystem crossing in aromatic amines

The fluorescence and phosphorescence spectra of the aromatic amines acridan, iminobibenzyl, and carbazole have been measured in Shpolskii matrices at 10 K. Under these conditions the emission exhibits a detailed vibrational structure which has been analyzed. The change of the polarization degree observed within the fluorescence spectra at 77 K, particularly pronounced in acridan and iminobibenzyl, is attributed to vibronic interaction between the closely lying S₁(¹A₁) and S₂(¹B₁) excited states. This process activates a b₁ vibration with a frequency of 1200 cm⁻¹ in the ground state. The appearance of a long-axis (b₁) polarized vibration (700 cm⁻¹) following the out-of-plane polarized 0-0 band of the phosphorescence of these amines at 77 K is suggested to arise from vibronic interactions in the triplet manifold. This second-order spin-orbit coupling (soc) process is superimposed upon the dominant first-order electronic soc mechanism, which couples the lowest π, π^* triplet with high-energy (σ, π)^* singlet states.     

Interpretation of electronic spectra by configuration analysis: Absorption spectra of monosubstituted naphthalenes with an electron-accepting group

The electronic absorption spectra of four monosubstituted naphthalenes with an electron-accepting group, 1- and 2-naphthonitriles and 1- and 2-naphthaldehydes, have been investigated by means of configuration analysis with particular attention to the dependence of spectra on the position of substitution. The results of molecular orbital calculations based on the Pariser-Parr-Pople method were analyzed in terms of locally excited states and charge-transfer configurations. The characteristic changes in location of the L_b, L_a, and B_b bands caused by the substitution at 1- or 2-position are adequately explained by the analysis for monosubstituted naphthalenes with an electron-accepting group as well as for those with an electron-donating group. The results of the present configuration analysis for naphthalene derivatives with an electron-accepting group are compared with the results for those with an electron-donating group.     

Relative partial photoionization cross-sections and photoelectron branching ratios of ethylene

Relative partial photoionization cross-sections and photoelectron branching ratios of the valence bands (~10–25 eV binding energy) of ethylene are reported over the photon energy ranges 18–100 eV and 21–100 eV, respectively. The four lowest ionization energy bands (1b⁻¹_1u, 1b⁻¹_1g, 3a⁻¹_g, and 1b⁻¹_2u) show monotonic cross-section decreases with photon energy from 33 eV, the 1b⁻¹_1u CC π band showing the least rapid decline. In contrast, the 2b⁻¹_3u and 2a⁻¹_g bands show almost constant cross-sections up to ~50 eV photon energy, followed by similar, although slower, monotonic decreases. This is attributed to the substantial carbon 2s character of the 2b_3u and 2a_g orbitais. The cross-section behaviour of all bands is interpreted with the aid of SCF-LCAO-MO calculations on the neutral molecule using the Gaussian-80 series of programs.     

Steady‐State and Time‐Resolved Emission Studies of 6‐Methoxy Quinoline

Abstract

Steady‐state absorption, fluorescence excitation, and emission spectra of 6‐methoxy quinoline (6‐MQ) were measured at room temperature in cyclohexane, dioxane, ethanol, acetonitrile, water, and water–dioxane solvents. Absorption spectra of cyclohexane, n‐hexane, and isopentane solutions show resolved vibronic structure at room temperature. However, the excitation spectrum of cyclohexane solution is structureless and is found to be emission wavelength dependent, indicating the formation of at least two distinct species in the ground state. Similar behavior was observed in dioxane and water–dioxane solutions. For all other solutions, the fluorescence excitation spectrum of 6‐MQ was found to be the same for different emissions. Emission of 6‐MQ in all solvents consisted of two bands with their maxima around 355 nm (I) and 430 nm (II), the actual positions and the relative intensities being dependent on the solvent used. The bands I and II were respectively attributed to normal and protonated/H‐bonded species of either ¹L_a or ¹L_b states or mixed (¹L_a/¹L_b) state of ππ* character. Fluorescence decay of this dye in all solvents monitored over each emission maximum showed biexponential behavior, and the analysis yielded two different lifetime components for each emission band. The short and long fluorescence decay components were respectively in the range of 0.30–3.00 ns and 18–20 ns. The observed emission characteristics coupled with the nature of the fluorescence polarization spectra and two different decay components for each emission suggest the existence of two different conformers having two different excited electronic states.     

The lowest singlet and triplet excited states of pyrazine

The phosphoresence, fluorescence and absorption spectra of pyrazine-h₄ and -d₄ have been obtained at 4°K in a benzene matrix. For comparison, those of the isotopically mixed crystal pyrazine-h₄ in d₄ were also taken. All these spectra show extremely sharp and well-resolved lines and reveal detailed vibronic structure.The coincidence of origins of absorption and emission shows that the lowest singlet state is an allowed transition, properly designated as ${}^1\text{B}{}_{\mathrm{3u}}\text{←}{}^1\text{A}{}_{\mathrm{1g}}$. The forbidden component ¹B_2g, predicted by both “exciton” and MO theories to be below the allowed component, must lie higher. Its exact location still remains uncertain.The phosphorescence spectrum, when compared with the singlet-triplet excitation spectrum, indicates that the lowest triplet state is also symmetry allowed, showing a strong 0-0 band and the coincidence of origins of absorption and emission. In accordance with previous work, the triplet state is designated as ³B_3u.The vibronic structure of the phosphorescence spectrum is very complicated. The first work on the analysis of this spectrum concluded that a simple progression of ν_6a exists. Under the high resolution attainable in the present experiments, the supposed ν_6a progression proves to have a composite structure, starting from the second member of the progression. Not only is the ν_9a hydrogen-bending mode present as shown by the appearance of the CD bending mode in the d₄ spectrum, but a band assigned as 2ν_6b was also identified. The latter's anomalous intensity in the phosphorescence spectrum is interpreted as due to the Fermi resonance with 2ν_6a and ν_9a bands. To help resolve the present controversy over the origin of the phosphoresence spectrum observed in crystalline pyrazine, detailed vibrational analyses of the emission spectra were made. The fluorescence spectrum has essentially the same vibronic structure as the phosphorescence spectrum.     

Assignments of the nπ singlet states of p-benzoquinone

The vapor phase fluorescence spectra of p-benzoquinone-h₄ and d₄ are reported and discussed in relation to the assignment of the low lying singlet states. The low temperature, polarized single crystal electronic absorption spectra of p-benzoquinone and several of its isotopic derivatives are reported. From the isotope shifts and band polarizations of the various vibronic origins, a detailed vibronic analysis is offered of the electronic absorption spectrum of p-benzoquinone which indicates a near degeneracy of the ¹A_u and ¹B_1g electronic states.     

Measurement of degree of polarization of fluorescence of pure anthracene crystalline film

The polarization ratio (I _b/I_a) of fluorescence of a monocrystalline film of pure anthracene is measured correcting for all probable errors. Comparison with decay-time data brings out that deviation from the value obtained from absorption measurements is due to a loss of intensity in the a-polarized fluorescence as compared to what is expected from absorption data. This is interpreted as an evidence that anthracene crystal fluorescence is emitted from regions of local lattice imperfections. It is confirmed that the first electronic transition takes place along the short axis of the anthracene molecule.     

Fluorescence and fluorescence excitation spectra of jet-cooled carbazole

The fluorescence excitation spectra of jet-cooled carbazole molecules at vibrational temperatures of 55 and 80 K and the fluorescence spectrum of these molecules excited by radiation at the frequency of a pure electronic transition are measured. As the vibrational temperature increases, the excitation spectra exhibit a series of lines of the same symmetry, which are caused by the interaction of the active vibration with a subensemble of optically inactive vibrations. The final symmetry of the totally and nontotally symmetric vibrations is determined from the shape of the rotational contours of the lines of vibronic transitions. The values of a decrease in the frequency of the nontotally symmetric vibrations in the first excited electronic state S ₁ due to their interaction with the electronic state S ₂ are calculated to be up to 100 cm^?1. The frequencies of the pure electronic transitions in the absorption and fluorescence spectra coincide with each other and are equal to 30809 cm^?1, the frequencies of vibrations in the ground state S ₀ exceeding the frequencies of the corresponding vibrations in the excited state S ₁. The degree of polarization of the integral fluorescence is determined for a series of vibronic transitions of the a ₁ and b ₂ final symmetry that are observed in the fluorescence excitation spectra, and the contribution of the intensity with the borrowed polarization θ_⊥ to the integral fluorescence is calculated. It is found that the intensity θ_⊥ is higher for the transitions of the b ₂ symmetry and can reach ≈50%.     

Indole in Argon Matrix: The Near UV Spectra.

Abstract

The near UV absorption, steady-state polarized fluorescence excitation and time–-resolved fluorescence emission spectra of indole in argon matrix are reported. The absorption maxima of the four lowest singlet transitions were identified at 35095 cm^?1(also the S_{1, 0} 0–0 band), 37650 cm^?1 (S_2,0), 47415 cm^?1 (S_3,0), and 51680 cm^?1 (S_4,0). No distinct 0–0 band of the second transition was identified but the linearly polarized, steady-state fluorescence excitation spectrum indicates an onset of weak S_2,0 bands on the blue side of the S_1,0 0–0 peak (35095 + 400 cm^?1). Only one fluorescence emission component, of 4.9±0.2 ns, was obtained by excitation over the S_{1, 0} 0–0 + 565 cm^?1 to S_1,0 0–0 - 245 cm^?1 domain. The reported data strongly suggest the ¹L_b ^?1A₁ and ¹L_a ^?1A₁assignment for the lowest and next lowest transitions, respectively.     

First-principles band-structure calculations as a tool for the quantitative interpretation of Raman spectra of high temperature superconductors

We have performed first-principles band structure calculations in order to investigate vibronic and optical properties of YBa₂Cu₃O₇. A formalism describing temperature dependent Raman spectra from such ab-initio results has been applied to the 500 cm^?1 apex oxygen mode and its overtone in good agreement with experimental results. The dynamical matrix of the five A_1g modes established by atomic-force calculations is studied in detail showing rather good agreement with experimental eigen-frequencies and normal coordinates. The effect of isotope substitutions on the phonon frequencies is investigated. We demonstrate that the calculated vibronic properties of high T_c materials are improved by applying a generalized gradient correction scheme for the treatment of exchange and correlation effects instead of the local-density approximation.     

STUDY OF THREE-PHOTON RESONANCE MULTIPHOTON IONIZATION SPECTROSCOPY OF 3p RYDBERG STATES OF m-DIMETHYLBENZENE WITHIN DYE Rh560

In this paper, we studied experimentally the three-photon resonance four-photon ionization spectroscopy of m-dimethylbenzene within dye Rh560. We found several new 3p Rydberg vibronie states and measured their polarization characters. With the help of the measured polarization quantities, we gave the assignment results of these vibronic states: 9b₀¹, A₁; 13₀¹, A₁; 19a₀¹, A₁; 8a₀¹, A₁.     

Electronic spectrum of 1,5-naphthyridine: Vapor spectra

Analyses of the vapor spectra of 1,5-naphthyridine-d₀ and -d₆ are presented. The spectra are characterized by two principal origins, one the true electronic origin, magnetic dipole allowed, ${}^1\text{B}{}_{\mathrm{g}}\text{←}{}^1\text{A}{}_{\mathrm{g}}$, 27 598.5 cm^?1 (-d₆ 27 676.9), and the other a vibronic origin, electricd-dipole allowed, corresponding to the activity of a low-frequency vibration 6a_u, 183 cm^?1 (-d₆ 163). Extensive sequence structure is evident and the relative intensities of the sequence bands associated with the two origins provide the strongest argument for their assignments. The absence of 6a_u as a major source of intensity in the hot bands is in agreement with vibronic coupling calculations which propose that in absorption intensity “flows” to the lower-frequency vibrations.     

The magnetic circular dichroism spectrum of the hexaquocobalt (II) ion in the infra-red region

The magnetic circular dichroism (MCD) and absorption spectra in the range 5500–10 250 cm^-1 of a single cubic crystal of [Co(H₂O)₆](BrO₃)₂ have been measured at various temperatures between 5 and 300 K. An analysis of the temperature variation of the zeroth absorption and MCD moments shows that the intensity of the E′ (⁴αT _1g ) → ⁴ T _2g transition is provided mainly through the two cobalt-oxygen t _1u vibrations. The signs and magnitudes of the overall b and c term are in reasonable accord with previously published calculations. The low energy side of the MCD band exhibits some zerophonon lines and a complex vibronic structure which appears to involve low energy lattice vibrations as well as the cobalt-oxygen skeletal vibrations.