Vibronic fluorescence and fluorescence excitation spectra of diphenyl oxazolyl benzene and its oxadiazol analogue

The fine-structure fluorescence and fluorescence excitation spectra of conjugated chain compounds—1,4-di(5-phenyl-2-oxazolyl) benzene and its oxadiazol analogue—are obtained at 4.2 K in an n-octane matrix using the Shpolskii method. The spectra are modeled by representing the band of each of the vibronic transitions as the sum of a zero-phonon line and a phonon wing with certain parameters (half-widths, Debye-Waller factors). The spectra calculated in this fashion coincide with the experimental spectra. This makes it possible to determine the relative intensities of vibronic transitions and refine the frequencies of the normal vibrations in the S ₀ and S*₁ states. The parameters of the Franck-Condon and Herzberg-Teller interactions in the molecules considered are determined. The influence of the replacement of one of the CH groups in the heterocycles with a N atom on the parameters determining the formation of vibronic spectra is considered.     

Specific features in the vibronic fluorescence spectra of analogues of 1,4-bis(5-phenyl-2-oxazolyl)benzene with oxadiazole and furan rings

The fine-structure fluorescence and fluorescence excitation spectra of conjugated chain compounds, namely, 2,5-bis(5-phenyl-1,3,4-oxadiazol-2-yl)furan (PDFDP) and 2,5-bis[5-(2,4-dimethylphenyl)-1,3,4-oxadiazol-2-yl]furan (XDFDX), were obtained by the Shpolskii method in an n-octane matrix at a temperature of 4.2 K. These spectra were simulated by representing the band of each of the vibronic transitions as the sum of a zero-phonon line and a phonon wing with the corresponding parameters, such as the half-widths of the spectral lines and the Debye-Waller factors. The results obtained made it possible to estimate the relative intensities of the vibronic transitions between the S ₀ and S*₁ states. The anharmonicity revealed in the conjugate spectra of fluorescence and fluorescence excitation of the PDFDP and XDFDX compounds was explained in terms of the interference of the Franck-Condon and Herzberg-Teller interactions occurring in the molecules under investigation. The influence of the substitution of the furan heterocycle (F) for the central benzene ring (P) in 1,4-bis-(5-phenyl-2-oxadiazolyl)benzene (PDPDP) on the parameters of the intramolecular interactions responsible for the formation of the vibronic spectra was considered.     

Comparative analysis of intramolecular interactions in trans-stilbene and 1,4-distyrylbenzene

We have analyzed the intensity distributions in fine-structure fluorescence and fluorescence excitation spectra of trans-stilbene in n-hexane at 4.2 K. Modeling the spectra by representing each of the vibronic transitions by a zero-phonon line and a phonon wing with certain parameters (widths, Debye-Waller factors) made it possible to determine relative intensities of vibronic transitions. The parameters of Franck-Condon and Herzberg-Teller interactions, which form the fine-structure spectra of stilbene, have been calculated and compared with previously obtained parameters of intramolecular interactions in 1,4-distyrylbenzene.     

Effect of the fluorine substitution in ethyl groups of 1,4-distyrylbenzene on the fine structure fluorescence and fluorescence excitation spectra

The fine-structure fluorescence and fluorescence excitation spectra of conjugated chain compounds, 1,4-distyrylbenzene (DSB) and its fluorine-substituted derivative α,ω-1,4-distyrylbenzene, have been obtained by the Shpolskii method in an n-octane matrix at a temperature of 4.2 K. These spectra have been simulated by representing the band of each of the vibronic transitions as the sum of a zero-phonon line and a phonon wing with the corresponding parameters, such as the half-widths of the spectral lines and the Debye-Waller factors. Based on this simulation, the relative intensities of vibronic transitions have been determined and the frequencies of normal vibrations in the S ₀ and S ₁^* states have been refined. It has been found that the energy of the purely electronic transition in the molecule of the fluorine-substituted derivative is higher by 950 cm⁻¹ compared to the unsubstituted DSB. The parameters of the Franck-Condon and Herzberg-Teller interactions have been determined. The observed violation of the mirror symmetry between the conjugated spectra is explained by the interference of intramolecular interactions.     

Quantitative analysis of intramolecular interactions of all-trans-α,ω-diphenylpolyenes with one to four double bonds

We have analyzed intensity distributions in fine structure fluorescence spectra of three all-trans-diphenylpolyenes with number of double bonds n = 1?4 in solutions in n-paraffins at 4.2 K. Modeling of spectra by representing each of the vibronic transitions by a zero-phonon line and a phonon wing with certain parameters (width, Debye-Waller factor) made it possible to determine the relative intensities of vibronic transitions. We have calculated and comparatively analyzed the parameters of intramolecular interactions that form fine structure spectra of stilbene and investigated compounds.     

Modeling vibronic spectra and excited states of polyenes with a parametric method

The structural-dynamic models of excited states and vibronic structure of absorption spectra of linear polyenes (R-(CH=CH)_n-R, R=H, CH₃, n=4, 5, 7) are calculated using the parametric method of the theory of vibronic spectra of such molecules. Good agreement is obtained between the calculated and experimental spectra. It is shown that the system of parameters of the method for the polyenes has a high degree of transferability in the series of related polyenes. The constructed models adequately reflect the real structure of the molecules in excited states and allow one to predict quantitatively the fine vibrational structure of the spectra, including relatively weak effects related to the methyl substitution. The dynamic of structural changes of the molecules upon their excitation is studied in the series of polyenes.     

The effect of annulation of benzene rings on the photophysics and electronic structure of tetraazachlorin molecules

The photophysics and electronic structure of tribenzotetraazachlorins (H₂, Zn, and Mg), which are novel analogues of phtalocyanines, have been studied experimentally and theoretically. At 293 K, the electronic absorption, fluorescence, and fluorescence excitation spectra are recorded and the fluorescence quantum yield and lifetime, as well as the quantum yield of singlet oxygen generation, are measured; at 77 K, the fluorescence, fluorescence excitation, and fluorescence polarization spectra are recorded and the fluorescence lifetime values are measured. The dependences of the absorption spectra and photophysical parameters on the structure variation are analyzed in detail. Quantum-chemical calculations of the electronic structure and absorption spectra of tribenzotetraazachlorins (H₂, Mg) are performed using the INDO/Sm method (modified INDO/S method) based on molecular-geometry optimization by the DFT PBE/TZVP method. The results of quantum-chemical calculations of the electronic absorption spectra are in very good agreement with the experimental data for the transitions to two lower electronic states.     

Spectroscopic characterization of structural isomers of naphthalene: 1-Phenyl-1-butyn-3-ene

Laser induced fluorescence (LIF), single vibronic level dispersed fluorescence (DFL) spectra, and high resolution rotationally resolved scans of the S₀–S₁ transition of the C₁₀H₈ isomer 1-phenyl-1-butyn-3-ene have been recorded under jet-cooled conditions. The S₀–S₁ origin of PAV at 34 922 cm⁻¹ is very weak. A vibronic band located 464.0 above the origin, assigned as 30¹₀, dominates the LIF excitation spectrum, with intensity arising from vibronic coupling with the S₂ state. High resolution scans of the S₀–S₁ origin and 30¹₀ vibronic bands determine that the former is a 65:35 a:b hybrid band, while 30¹₀ is a pure a-type band, confirming the role for vibronic coupling and identifying the coupled state as the S₂ state. DFL spectra of all vibronic bands in the first 800 cm⁻¹ of the spectrum were recorded. A near-complete assignment of the vibronic structure in both S₀ and S₁ states is obtained. Herzberg–Teller vibronic coupling is carried by two vibrations, ν₂₈ and ν₃₀, involving in-plane deformations of the vinylacetylene side chain, leading to Duschinsky mixing evident in the intensities of transitions in excitation and DFL spectra. Extensive Duschinsky mixing is also present among the lowest five out-of-plane vibrational modes, involving motion of the side chain. Comparison with the results of DFT B3LYP and TDDFT calculations with a 6-311+G(d,p) basis set confirm and strengthen the assignments.     

Effect of Deuteration on Quasiline Electronic‐Vibrational Spectra of Phthalocyanine

Quasiline electronicvibrational spectra of fluorescence and absorption (excitation of fluorescence in selective recording) of the molecules of phthalocyanine deuterated around the periphery of benzene rings (H₂Phcd ₁₆) and the center of the macrocycle (D₂Phc) are obtained. The vibrational frequencies of the ground state are almost insensitive to this deuteration (except for vibrations with the participation of angular deformations). In excitation spectra, changes in deuteration are more pronounced due to the effects of nonadiabatic vibronic interaction of the vibrational sublevels of the S ₁ state and of the purely electronic level S ₂.     

Fermi-type resonance in quasi-linear fluorescence excitation spectra of triazatetrabenzoporphine

The effect of deuteration of the central NH groups on the quasi-linear fluorescence and fluorescence excitation (with selective monitoring) spectra for triazatetrabenzoporphine, a close analog of phthalocyanine, has been investigated at 77K in n-nonane. Vibrational analysis of the spectra was carried out. The normal mode frequencies were determined for the electronic states S₀ (from fluorescence spectra) and S₁ (for fluorescence excitation spectra). It has been established that N-deuteration lowers the frequency of a vibration involving inplane NH bending down to ∼990 cm⁻¹ and leads to resonant vibrational-electronic (vibronic) interaction of Fermi-type resonance between the zero level of the S₂ state and the vibronic level of the S₁ state upon excitation of this mode. Thereby the possibility of the “vibronic analog of Fermi resonance” (a term coined by G. Herzberg) occurring in a simple (two-component) variant of phthalocyanine-type molecules has been shown. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 796–803, November–December, 2008.     

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%.     

Identification of the SO2 cold vibronic bands in the 32 200–33 300 cm−1 region

Summary The fluorescence excitation spectrum of SO₂ in the 32 200–33 300 cm⁻¹ energy region was recorded, at very low rotational temperature, in a pulsed supersonic jet. The band centres and relative intensities of about 60 well-resolved vibronic bands were determined in this region, which extends the previously available data by 800 cm⁻¹. Single vibronic level fluorescence spectra of two neighbouring vibronic bands in theD-band region along with a few filtered excitation spectra are also presented as an example of the resolution for the listed bands. The authors of this paper have agreed to not receive the proofs for correction.     

Vibronic structure of the 3s Rydberg state of the 2-methylallyl radical

Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled 2-methylallyl (C₄H₇) radicals provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following one-photon and two-photon excitation of rovibronically cold 2-methylallyl radicals and its isotopologues C₄H₄D₃ and C₄D₇ reveals transitions to more than 30 vibrational levels in the 3s Rydberg state that are identified and reassigned on the basis of predictions from ab initio calculations and results from pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained with resonant multiphoton excitation via selected intermediate states. Depletion spectroscopy reveals transitions to short-lived 3p Rydberg states that have a large oscillator strength.     

Autowave instability in refractive crystals

The intensities of vibronic lines are experimentally measured in fluorescence and fluorescence excitation spectra of jet-cooled anthracene. An original method is developed for calculating geometrical parameters of benzene hydrocarbons in the ground and excited electronic states. Using these parameters, the intensities of vibronic lines in fluorescence and absorption spectra of anthracene are calculated in the Franck-Condon approximation taking into account the mixing of all the twelve normal coordinates of totally symmetric vibrational modes. After correction for the quantum yield of fluorescence, good agreement is obtained between the calculated line intensities in the absorption spectrum and the measured line intensities in the fluorescence excitation spectrum. Based on these data, a new assignment of the lines in the fluorescence excitation spectrum corresponding to totally symmetric modes 7 and 8 is suggested.     

Fluorescence studies of retinol and retinyl acetate

The polarized emission study of all-trans retinol and retinyl acetate in solid films at room temperature has been carried out. The shape of the absorption and fluorescence is typical of Franck-Condon forbidden bands. The high positive polarization of the fluorescence excitation and the emission (when excited into main absorption band due to 1_Bu ← 1_Ag transition) suggests that the lowest excited singlet state of retinols has a large amount of 1_Bu character. The explanation for the high positive polarization involving strong vibronic interactions suggesting 1_Ag - (a very weakly allowed state) being the lowest excited singlet has also been considered.     

Low temperature laser fluorescence and excitation spectra of free base phthalocyanine in normal alkanes matrices (Shpolskii effect)

Excitation and fluorescence spectra of free base phthalocyanine were studied in matrices of normal alkanes (C₈H₁₈, C₁₂H₂₆, C₁₆H₃₄) at low temperatures (5 to 30 K). Narrow band excitation of fluorescence using a pulsed tunable dye laser was used for site selection to eliminate ambiguities due to impurities and multiple sites. Fluorescence and excitation spectra show quasiline structure. Multiplicity of 0-0 transitions depends on the chain length of normal alkanes. The spectra and frequencies of normal vibrations are compared with those of phthalocyanine in other n-alkanes (C₉H₂₀, C₁₀H₂₂) and noble gas matrices (Ar, Ne) under different excitation conditions.     

Magnetic field effect on the H2CS fluorescence from the first excited singlet state Ã1A2

Fluorescence intensity in thioformaldehide vapours (H₂CS), excited to the ÃA₂ different vibronic levels of the ùA₂ ? [Xtilde]¹A₁ transition, were measured as a function of an external magnetic field. On excitation to these levels, dynamics in zero and non-zero field may be described in the small-molecule limit, with fluorescence exhibiting an almost exponential decay. A magnetic field changes the integrated intensity and decay lifetime of the thioformal-dehide fluorescence induced from different vibronic levels of the ù A₂ state. We found that the magnetic field effect grows at lower gas pressures. The measured field dependences of the magnetic field effect can be fitted using field-saturated functions. The measured data were explained by the indirect mechanism theory (nuclear-spin and electron-spin decoupling mechnism).     

Experimental determination and interpretation of the fluorescence and fluorescence excitation spectra of chrysene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of jet-cooled chrysene are measured. The frequencies of in-plane vibrations in the ground and first excited singlet electronic states, as well as the relative intensities of transitions between them, are calculated with the MO/M8ST method. Based on these data, experimental spectra are interpreted. In the fluorescence excitation spectrum, the position of the line of the 0–0 transition (28 195 ± 1 cm^?1), which is the most intense, is determined. In the experimental fluorescence excitation spectrum, 21 lines correspond to fundamental vibrations (altogether, 37 lines are attributed). This supports our assignment and is consistent with the group-theoretical analysis of vibronic interactions. Upon excitation at the frequency of the 0–0 transition, 10 lines corresponding to the excitation of fundamental vibrations are detected, and all 17 lines observed are attributed. In the fluorescence excitation spectrum, the standard deviation between the calculated and measured frequencies of attributed fundamental vibrations is 19 cm^?1, while that in the fluorescence spectrum is 15 cm^?1.     

Spectra of the selective heat radiation of Yb2O3 under the laser thermal excitation

The dependence of the spectra of the near-IR and visible selective heat radiation (SHR) of the Yb₂O₃ polycrystals that are synthesized using the laser thermal method on the excitation intensity of the CW electric discharge CO₂ laser at the wavelength λ = 10.6 μm is experimentally studied. The SHR spectra are determined by the multiphonon excitation of the vibronic states of the ² F _5/2 term in the Yb³⁺ ions and the radiative transitions to the vibronic states of the ground term ² F _7/2.The laser heating of the polycrystals to the melting point causes the anomalous growth of the SHR spectral peaks in the wavelength range λ ≥ 1040 nm due to an increase in the intensity related to an increase in the probabilities of the radiative vibronic transitions owing to the thermal increase in the phonon density. The effective conversion of the thermal energy of the Yb₂O₃ polycrystals into the SHR indicate the significant role of the radiative cooling of surface.     

Jet Spectroscopy of theD12B1–D01B1Transition of thep-Cyanobenzyl Radical

We have generated thep-cyanobenzyl radical in supersonic free expansion, and measured the vibrationally and rotationally resolved laser induced fluorescence (LIF) excitation spectra and the LIF dispersed spectra from the single vibronic levels (SVL) in the green-blue region. The lowest energy band at 20 738 cm⁻¹with the strongest intensity in the excitation spectrum has been assigned to the 0⁰₀band of the visible spectrum, on the basis of the vibronic structures in the SVL dispersed spectra. Based on the band type of the 0⁰₀band,a-type, determined from the rotationally resolved LIF excitation spectrum, we have definitely assigned the visible band to theD₁2²B₁–D₀1²B₁electronic transition. We have found, on the grounds of the vibrational analysis of the dispersed spectra, that the vibronic structure of the 2²B₁–1²B₁electronic transition of the benzyl type is characterized by totally symmetric fundamental modes, 1, 8a, and 9a.