Manifestation of vibronic intensity borrowing in fluorescence spectra of metalloporphyrins

In selective laser excitation and at T=4.2 K, fine-structure spectra of the fluorescence of the complexes of Mg, Zn, In, and TiO with octaethylporphyrin are obtained. It is shown that the fine-structure fluorescence spectra of these compounds are formed to a large aegree by ribronic interaction between quasi-degenerate S₁ and S₂ electron states. An increase in the relative intensities of a number of negatively polarized fluorescence lines in displacement of the excitation line from a longwave edge of the band of an S₀→S₁ transition in the shortwave direction is revealed. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 518–522, July–August, 1999.     

Interpretation of resonance Raman spectra of Zn-phthalocyanine and Zn-phthalocyanine-d<Subscript>16</Subscript> based on the density functional method

We have used the density functional method (DFT) to calculate the geometric structure and the frequencies of even (gerade) vibrations of the Zn-phthalocyanine and Zn-phthalocyanine-d₁₆ molecules, and we have refined the interpretation of the resonance Raman spectra and the fine-structure fluorescence spectra. We observed a dependence of the frequencies of both stretching and bending vibrations of the aza bridges on the nature of the central metal atom. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 296–299, May–June, 2007.     

Absorption,fluorescence, and fluorescence excitation spectra of free molecules of indole and its derivatives

We have obtained and analyzed the absorption, fluorescence, and fluorescence excitation spectra of indole vapor, N-acetyl-L-tryptophan vapor, and 3-indole aldehyde vapor. From analysis of the dependence of the fluorescence spectrum of the free indole molecules on the wavelength of the exciting radiation λ_ex, it follows that emission of fluorescence occurs when the molecules undergo a transition from the one electronically excited state ¹L_b. The fluorescence spectra of the studied compounds are insignificantly different, suggesting a major role for the indole chromophore in formation of the compounds. The absorption spectrum of N-acetyl-L-tryptophan, in which the group of atoms is added to the indole ring through a-C-C bond, is similar to the spectrum of indole, while the spectrum of 3-indole aldehyde is significantly different from the indole spectrum due to the effect of the C=O group conjugated with the indole ring. The fluorescence excitation spectra are considerably different from the absorption spectra. This is associated with the strong dependence of the quantum yield for the free molecules on λ_ex. Qualitatively, they are mirror-symmetric to the fluorescence spectra of the stodied compounds. Analysis of the data obtained provides a basis for assuming that in the case of free molecules of indole and its derivatives, the ¹L_a absorption in the extreme long-wavelength region of the spectrum does not overlap ¹L_b absorption. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 218–222, March–April, 2007.     

Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

We have recorded the fluorescence excitation spectra of three heterocyclic compounds with a chain structure [BPO (2-phenyl-5-(4-diphenylyl)oxazole), POPOP (1,4-di[2-(5-phenyloxazolyl)]benzene, and TOPOT (1,4-di[2-(5-n-tolyloxazolyl)]benzene] and the fluorescence spectra of POPOP, under conditions where the molecules were cooled in an ultrasonic helium jet. A line structure is observed in the spectra of POPOP and TOPOT; for the BPO molecules, whose configuration changes considerably during electronic excitation, vibrational structure is apparent only in the low-frequency region of the excitation spectrum, and a diffuse spectrum is recorded starting from ν ₀ ⁰ + 200 cm⁻¹. For all the compounds, in the spectra we recorded vibrations with frequencies up to 100 cm⁻¹, arising due to the flexibility of the molecular structure. The rotational contours of the lines for the electronic and vibronic transitions of the POPOP molecules (T_rot = 10.5 K) and TOPOT molecules (T_rot = 15 K) are structureless and bell-shaped. The degree of polarization of the fluorescence P_fl for the jet-cooled POPOP molecules for excitation of vibrations along the absorption band up to 2000 cm⁻¹ above ν ₀ ⁰ is practically constant (∼8.4%) and matches P_fl for high-temperature vapors. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 728–734, November–December, 2006.     

Fluorescence polarization of helical molecules cooled in a supersonic jet

The β-binaphthylene oxide molecules studied under supersonic cooling conditions have a number of specific properties due to their nonplanarity. Low-frequency vibrations of the molecules in the excited S1 state are higher than the frequencies for the S0 state, and conversely the high-frequency vibrations have lower frequencies. The S₀-S₂ fluorescence excitation spectrum is structureless. The absence of a Q branch in the rotational contour of the line for the purely electronic transition indicates that it is substantially broadened and shifted toward shorter wavelengths as a result of rotational perturbations of the helical structure of the molecule. Multiplet lines in the spectra of β-binaphthylene oxide complexes with argon, krypton, and xenon correspond to different isomeric complexes. Their bond energies are below those observed previously for planar polycyclic molecules such as perilene, fluorene, and carbazole. The greater number of isomers with xenon is due to strengthening of the bond in the van der Waals complex and the nonequivalence of the position of the xenon atoms on the outside and inside of the helical molecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 473–477, July–August, 2006.     

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.     

Spectral fluorescence and polarization characteristics of <Emphasis Type="Italic">Z,Z</Emphasis>-bilirubin IXα

We have studied the spectral fluorescence and polarization characteristics of Z,Z-bilirubin IXα, at room temperature in chloroform and in aqueous buffer medium, within an equilibrium complex with human serum albumin (HSA), and also under low temperature conditions (T = −100°C) in isobutyl alcohol. We have observed a bathochromic shift of the fluorescence spectra, which is most pronounced for the bilirubin-albumin complex. The following are considered as possible reasons for the observed dependence of the position of the fluorescence (fluorescence excitation) spectra on the excitation (detection) wavelength: structural and spectral differences between the chromophores making up the bilirubin molecule; conformational heterogeneity of the pigment in solution; a contribution to the fluorescence from molecules which have not completed the vibrational relaxation process; inhomogeneous orientational broadening of the levels; heterogeneity of the microenvironment of the chromophores in the protein matrix. We show that polarized fluorescence of bilirubin occurs at room temperature, due to the anomalously short fluorescence lifetime τ (picosecond or subpicosecond ranges). Despite such a short τ, the absorption and emission polarization spectra suggest the presence of intramolecular nonradiative singlet-singlet energy transfer when bilirubin is excited to high vibrational sublevels of the S₁ state (degree of polarization p = 0.11–0.12). When fluorescence is excited on the long-wavelength slope of the absorption band, no transfer occurs: the degree of polarization (p = 0.46−0.47) is close to the limiting value (p = 0.50). We discuss the question of the role played by exciton interactions between chromophores in the bilirubin molecule when it is excited. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 108–119, January–February, 2007.     

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.     

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.     

Fluorescent properties and spontaneous Raman spectroscopy of new ketocyanine probes in organic solvents

We have used fluorescence spectroscopy and spontaneous Raman spectroscopy to study the characteristics of two ketocyanine dyes: 2,5-di[(E)-1-(4-diethylaminophenyl)methylidene]-1-cyclopentanone (CPET) and 2-[(E)-1-(4-diethylaminophenyl)methylidene]-5-{(E)-1-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecalin) phenyl]methylidene}-1-cyclopentanone (CPMR) in organic solvents. The position of their electronic spectra depends strongly on the polarity of the solvent. We measured the dipole moments of the dyes in the equilibrium ground state and the Franck-Condon excited state. In mixtures of neutral nonpolar toluene with aprotic polar dimethylsulfoxide, we observe inhomogeneous broadening of the electronic spectra for the indicated compounds, due to fluctuations in solution of the intermolecular interaction energy. The time-resolved characteristics of fluorescence obtained suggest formation of an intermolecular hydrogen bond between the dye and the surrounding medium in a toluene-ethanol mixture. We measured the Raman spectra of CPET and CPMR in different organic solvents. The most intense lines in the 1582–1591 cm⁻¹ region can be assigned to stretching of the phenyl rings of the molecules; the lines in the 831–842 cm⁻¹ region can be assigned to a cyclopentanone ring mode; the lines at 1186–1195 cm⁻¹ can be assigned to stretching of the =C-C-bond of the phenyl ring and rocking of the H atoms of the phenyl ring. We have observed that the position and width of the lines for the stretching vibrations of the ketocyanines depend substantially on the polarity of the surrounding medium. The studied dyes can be used as probes for studying different biological systems by site-selective laser spectroscopy and Raman spectroscopy. The fact that these two methods can be used simultaneously for diagnostics of biosystems is an important advantage of ketocyanine dyes compared with other known probes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 763–769, November–December, 2006.     

Absorption,fluorescence, and SERS spectra of sanguinarine at different pH values

We have studied the absorption, fluorescence, and surface-enhanced Raman scattering (SERS) spectra of sanguinarine using a silver hydrosol and an electrochemical cell with a silver working electrode for different pH values in the medium. We carried out quantum chemical calculations in order to interpret the electronic and vibrational spectra and to establish their correlations with the structure of the molecules. We optimized the structure and determined the spectral characteristics of the cationic and neutral forms of the sanguinarine molecules in solution and adsorbed on the surface of an anodized Ag electrode for different potentials. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 604–609, September–October, 2007.     

Fluorescence excitation spectra of jet-cooled carbazole complexes with monohydric alcohols

We have analyzed the fluorescence excitation spectra of carbazole complexes with a single molecule of methyl, deuterated methyl, ethyl, and propyl (1-propanol and 2-propanol) alcohols, cooled in a supersonic jet. We have determined the shifts in the fluorescence excitation spectra of the complexes relative to the frequency of the purely electronic transition of unbound carbazole. They occur as a result of formation of hydrogen bonds between the N-H group of the carbazole and the OH group of the alcohols. The frequencies of stretching vibrations of the hydrogen bonds with different alcohols vary within the range 150–157 cm⁻¹, while the frequencies of the bending vibrations vary in the range 21–22.9 cm⁻¹. From the shape of the rotational contours of the bands for the purely electronic and vibronic transitions of the complexes, we determined that they belonged to rotational conformers. We calculated the equilibrium configurations of the complexes in the ground state. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 756–760, November–December, 2007.     

Spectral and kinetic properties of fluorescence of immunoactive steroids in the gas phase

We have used steady-state fluorescence spectroscopy and pulsed kinetic fluorimetry with high time resolution to experimentally study the spectral and temporal characteristics of luminescence of immunoactive 8-aza-D-homogona-1,3,5(10), 13-tetraene-12,17a-dione (8-aza-D-homogonane) molecules in the gas phase. We have established the existence of several centers emitting long-wavelength and short-wavelength fluorescence. The fluorescence of high-temperature 8-aza-D-homogonane vapor (T = 550 K) when excited by radiation with λ_ex = 266 nm is represented by two spectrally separated emission bands with maxima λ _max ^fl = 465 nm and λ _max ^fl = 365 nm. Analysis of the distribution of fluorescence decay times for 8-aza-D-homogonane showed that in the spectral range of the emission wavelengths 360–590 nm, the fluorescence decay kinetics contains three components with average lifetimes <200 psec, 2.8 nsec and 13.5 nsec. The multicenter nature of luminescence of 8-aza-D-homogonane was confirmed by direct measurements of instantaneous fluorescence spectra in different stages of luminescence decay. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 309–314, May–June, 2006.     

Experimental determination and interpretation of fluorescence and fluorescence excitation spectra of 1,2-benzanthracene cooled in supersonic jet

We measured the fluorescence and fluorescence excitation spectra of supersonic jet-cooled 1,2-benzanthracene. Using the MO/M8ST method, we calculated the frequencies of in-plane vibrations in the ground and first excited singlet electronic states, and, in the Franck-Condon approximation, we calculated the intensities of transitions between them. Experimental spectra are interpreted based on these data. In the fluorescence excitation spectrum, the position of the line of the 0–0 transition (26535 ± 1 cm⁻¹), which is the most intense, is determined.     

Fine-structure spectra of metal complexes of porphin in tetrahydrofuran at low temperatures: Manifestation of nonplanarity effects

The fine-structure fluorescence spectra of Mg and Zn porphins in solid tetrahydrofuran matrices at the liquid helium temperature are recorded for the first time. The fluorescence spectra of Mg porphin molecules deposited from the gas phase on a sapphire substrate simultaneously with tetrahydrofuran molecules are measured. Based on the data obtained from the fluorescence and fluorescence excitation spectra, it is ascertained that there are two noninteracting spectrally different long-and short-wavelength forms of metal complexes of porphins in the ground state. In the case of Mg porphin, the spectral gap for these two forms at 4.2 K amounts to 330 cm^?1. The short-wavelength form is attributed to the nonplanar saddle conformation of a porphin molecule, while the long-wavelength form is associated with the nonplanar domed conformation, in which the central metal ion is displaced out of the plane of the porphyrin ligand. The fine-structure fluorescence spectra of both forms of Mg and Zn porphins are measured in tetrahydrofuran at 4.2 K upon selective laser excitation. The frequencies of the normal vibrations in the ground electronic state are determined and the reasons for the differences in the vibrational frequencies of the forms are discussed.     

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.     

Calculation and interpretation of IR and resonant raman spectra of 5-halosubstituted uracils

We have used valence optical theory to carry out calculation and analysis of in-plane vibrations and intensities of IR spectra for isolated 5-fluorouracil and 5-bromouracil molecules. We give a complete interpretation of the corresponding bands in the absorption spectra. We have carried out a quantum mechanical calculations of the relative intensities in the resonant Raman spectra of 5-fluorouracil and 5-chlorouracil. The calculated spectra for the molecular models obtained agree quantitatively with the experimental spectra, and reproduce the observed characteristic spectral differences in the series of molecules: uracil, 5-fluorouracil, 5-chlorouracil, and 5-bromouracil. The models obtained for the molecules can be used for calculation and analysis of the spectra of other halosubstituted nucleic acid bases. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 437–442, July–August, 2006.     

Luminescent spectral characteristics of eosin in solutions of human serum albumin when denatured by treatment with sodium dodecyl sulfate

From analysis of the fluorescence spectra of eosin molecules in a solution with human serum albumin (HSA), we have obtained information about the dynamics of protein conformational rearrangements during denaturing of the protein when treated with sodium dodecyl sulfate (SDS) for different pH values of the solution. We hypothesize that HSA denaturing in the presence of SDS occurs in two stages: the first stage is loosening of the protein globules, and the second stage is complete unfolding of the protein molecules. We have shown that denaturating of the protein in the presence of SDS passes through both stages for a solution pH below the isoelectric point of the albumin, while the denaturing stops in the first stage for a solution pH above the isoelectric point of the albumin. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 661–665, September–October, 2006.     

Fine-structure spectroscopy of 2-methylnaphthalene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of 2-methylnaphthalene molecules cooled in a supersonic jet are measured. The frequencies of vibrations in the S ₀ and S ₁ states, as well as the relative intensities of electronic-vibrational transitions in the fluorescence and fluorescence excitation spectra, are calculated with the semiempirical MO/M8ST method. The intensities are calculated in the Franck-Condon approximation taking into account the mixing of all the 38 totally symmetric normal vibrations. Based on the calculations, most observed spectral lines are assigned. It is shown that the calculation accuracy of the method is high enough for it to be used to interpret the spectra of molecules of aromatic compounds such as substituted naphthalenes. It is found that the main contribution to the fluorescence spectrum is made by four optically active vibrations.     

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.