Calculation and interpretation of the fine structure fluorescence spectra of anthracene upon resonance excitation of vibronic states

The vibrational structure of the spectra of fluorescence of anthracene obtained upon resonance excitation of vibronic states is calculated and analyzed by the parametric method of the theory of the vibronic spectra of complex molecules. The theoretical and experimental spectra agree qualitatively with each other, which indicates that this method of modeling such spectra is efficient. The parameterization of molecular models obtained upon calculation of the ordinary fluorescence and absorption spectra is completely applicable to the calculation of the fluorescence spectra considered. A total interpretation of the spectra is presented.     

Theoretical Study of the Vibronic Structure of the Absorption and Fluorescence Spectra of Thiazine Dyes

Russian Physics Journal - Theoretical modeling of changes in the vibronic absorption and fluorescence spectra in the molecules of two dyes of the thiazine series – methylene blue and...     

Modeling of the time-resolved vibronic spectra of polyatomic molecules: The formulation of the problem and analysis of kinetic equations

A semiempirical parametric method is proposed for modeling three-dimensional (time-resolved) vibronic spectra of polyatomic molecules. The method is based on the use of the fragment approach in the formation of molecular models for excited electronic states and parametrization of these molecular fragments by modeling conventional (one-dimensional) absorption and fluorescence spectra of polyatomic molecules. All matrix elements that are required for calculations of the spectra can be found by the methods developed. The time dependences of the populations of a great number (>10³) of vibronic levels can be most conveniently found by using the iterative numerical method of integration of kinetic equations. Convenient numerical algorithms and specialized software for PC are developed. Computer experiments showed the possibility of the real-time modeling three-dimensional spectra of polyatomic molecules containing several tens of atoms.     

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.     

Application of the method of selective fluorescence excitation to investigation of complexation and solvation processes of polar organic dye molecules in binary solvents

It is proposed to use the method of selective fluorescence excitation to find absorption spectra (fluorescence excitation spectra) of 1 : 1 primary solvated complexes between polar molecules of an organic dye and the active component of a binary solvent, whose neutral component is a nonpolar or low-polarity liquid. The technique was tested with diluted solutions of 4-dimethylaminochalcone (4-DMC) in mixtures of ethylbenzene with dimethyl formamide at extremely low contents of the latter. It is shown that the experimental absolute shift of the long-wavelength vibronic absorption band of three-component DMC solutions is in a good quantitative agreement with the analogous shift obtained independently based on the semi-empirical theory describing the joint effect of nonlinear (complexation) and linear (solvation) dipole-dipole interactions on the shift of spectral bands.     

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.     

Site-selection optical spectra of bacteriochlorophyll and bacteriopheophytin in frozen solutions

Site-selection spectra of title compounds in different frozen solvents at 5K have been obtained: fluorescence spectra on selective excitation in vibronic as well as in the O-O absorption region and excitation spectra with narrow-band fluorescence recording. Frequencies of vibrational modes active in fluorescence and excitation spectra of bacteriochlorophyll a (BChl) and its metal-free derivative have been determined from these fine-line spectra. Most favourable vibronic line-to-background intensity ratios have been found in non-polar aprotic glassy environments (triethylamine, di-iso-amylether). The intensity of zero-phonon lines in microcrystallic protic matrices was low, indicating strong electron-phonon coupling. The vibrational frequencies of the excited electronic state characteristic of axially (at Mg atom) mono- and disolvated BChl species have been identified. Narrow spectral holes of about 20% of the initial absorption could be burned with ≈10^-4 quantum yield within the O-O band of BChl and bacteriopheophytin.     

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.     

Electronic spectra of cationic forms of meso-tetrapropylporphin in a nanoporous silicate gel matrix

We have studied the fluorescence and fluorescence excitation spectra at 300 K, 77 K, and 4.2 K for silicate gel matrices colored with meso-tetrapropylporphin by impregnation of the matrix with a solution of the pigment. Comparison of the data obtained with the absorption spectra in acidified solutions and analysis of the low-temperature fine-structure vibronic spectra, and also taking into account data obtained earlier for octaethylporphin in a xerogel showed formation of two cationic forms of meso-tetrapropylporphin in the gel matrix: the short-wavelength form has a dicationic structure, while the long-wavelength form has a monocationic structure. We have traced out the correlations of the vibrational structure in the spectra of the dicationic form with data for the porphin dication, and we have drawn a number of conclusions concerning the normal vibrational modes that are active in the vibronic fluorescence and absorption spectra of the studied cationic forms. Using the AM1 semiempirical quantum chemical method, we optimized the geometry of the mesotetrapropylporphin dication: the most stable of the possible conformers is the dication structure with saddleshaped macrocycle nonplanarity. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 453–461, July–August, 2006.     

Intracavity Laser Spectroscopy of NiCl System G: Identification of a [13.0] Π3/2 State

The (0,0) vibronic band of NiCl system G with a bandhead near 12 961 cm⁻¹ was recorded at high resolution in absorption using intracavity laser spectroscopy (ILS). For the ILS absorption spectra, the NiCl molecules were produced in a nickel hollow cathode, operated with a small amount of CCl₄, and line positions were referenced to iodine spectra. Fourier transform (FT) emission spectroscopy was used to record an extensive region of the spectrum used in a vibronic analysis of system G. For the FT spectra, excited NiCl molecules were produced in a high-temperature King-type carbon tube furnace. We show that this transition is the (0,0) vibronic band associated with a newly identified ²Π_3/2 excited state and the X²Π_3/2 ground state. The molecular constants for the new ²Π_3/2 electronic state are derived from the rotational analysis. Improved vibronic constants for the band are obtained from analysis of the FT spectra.     

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.     

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.     

Extreme narrowing of bands in the fluorescence excitation spectra of organic molecules in solid solutions

Extreme narrowing of bands in the fluorescence excitation spectra of some organic molecules is found. This narrowing is observed when the excitation spectrum of a narrow spectral interval of the fluorescence band is recorded. The effect is observed in a wide variety of matrices and permits one to determine exactly the vibronic structure of the excited electronic state of the dissolved 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%.     

Algorithm for solving the inverse vibronic problem on the basis of SVL fluorescence spectra

Computer methods whereby the inverse vibronic problem is solved on the basis of resonance fluorescence spectra with the use of modern quantum-mechanical methods for constructing structuraldynamic models of polyatomic molecules are discussed. An algorithm is proposed for solving the inverse vibronic problem according to resonance fluorescence spectra under laser excitation, and the corresponding calculation programs are constructed. The initial program data are acquired by means of an original software package which implements the scaling of quantum-mechanical force fields in two electronic states. The Duschinsky matrix and the initial matrix of shifts in normal coordinates caused by electron excitation are calculated in the Cartesian and natural vibrational coordinates. The program data are taken from quantum-molecular models based on calculations performed via ab initio modern quantum-mechanical methods and density functional theory. The algorithm is tested through the calculation of a model molecular system.     

Forbidden character in electronic spectra of mono-halonaphthalenes

The singlet-singlet absorption and emission spectra of α-fluoro and the absorption spectra of α-chloro-, α-iodo-, and β-bromo-naphthalenes have been photographed and analyzed. The absorption spectra of all the four molecules show the presence of two discrete systems of bands, and the emission spectrum of α-fluoronaphthalene corresponds to the longer-wavelength system of absorption. With the α-chloro- and α-iodo-naphthalenes, the longer-wavelength system shows the appearance of pure electronic transition with weak bands, while the corresponding transitions in case of α-fluoro- and β-bromo-naphthalenes appear with the most intense bands of the system, as expected theoretically. The appearance of strong vibronic and weak electronic bands in the longer-wavelength system of the former two molecules has been interpreted as the interaction of totally symmetric vibrations, a rare example in the literature.     

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.     

Calculation and interpretation of vibronic absorption and fluorescence spectra of the first electronic nπ* transitions of pyridine and pyrimidine

We have calculated vibronic spectra of the first electronic nπ* transitions of pyridine and pyrimidine in the isolated state using the DFT method in the Franck-Condon approximation. Vibrational spectra for the ground and excited states have been calculated in the anharmonic approximation, which allowed us to refine the assignment of normal vibrations of pyridine and pyrimidine. We have done a complete interpretation of the vibrational structure of the absorption and fluorescence spectra of pyridine and pyrimidine. It has been shown that Fermi resonances between fundamental and combination vibrations and overtones 12 and 16b + 4, 6a and 2 × 16b affect the formation of the vibrational structure of electronic spectra of pyrimidine. Good agreement between calculated and experimental spectra confirms the correctness of the models of the two molecules in their ground and excited states, which makes it possible to use the models in further investigations of various properties of these molecules in electronically excited states, e.g., tautomerism of pyrimidine bases of nucleic acids.     

Electronic and vibronic spectra of Pr in LiYF4

The polarized absorption and fluorescence spectra of Pr³⁺ in single crystals of LiYF₄ having the scheelite structure have been investigated and assignments made on the basis of S₄ site symmetry. Strong vibronic coupling associated with the ³H₄→³H₅, ¹D₂ transitions in absorption and the ³P₀→³H_4,6 transitions in fluorescence was observed. Using selection rules for vibronic coupling and the known k = 0 phonons, these “extra” features of the spectrum can be accounted for in polarization and frequency.     

金纳米粒子掺杂DNA-CTMA-DPFP薄膜的表面增强拉曼散射特性

采用柠檬酸三钠还原氯金酸和离子交换法制备金纳米粒子掺杂DNA-CTMA材料,利用钯催化反应合成9,9-二乙基-2,7-二-(4-吡啶)芴荧光染料(DPFP),将DPFP与DNA-CTMA混合后,旋凃制备金纳米粒子掺杂的DNA-CTMA-DPFP薄膜样品。通过吸收光谱、荧光光谱和拉曼光谱的测量,研究了薄膜样品的光学特性和表面增强拉曼散射(SERS)特性。实验结果表明,薄膜样品在300～360 nm的吸收主要来自DPFP,在500～700 nm的吸收来自样品中金纳米粒子的局域表面等离子共振;样品在370,386,408 nm处的荧光峰分别对应DPFP的S₁₀-S₀₀、S₁₀-S₀₁和S₁₀-S₀₂能级的电子振动跃迁;在785 nm激光激发下,薄膜样品的拉曼散射主要来自DPFP分子,随着金纳米粒子掺杂比的增大,DPFP分子的拉曼散射峰强度逐渐增强。因此,金纳米粒子掺杂DNA-CTMA薄膜适合作为多种染料分子的SERS基底。