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.     

Structure and spectral-luminescent properties of 6-isoxazolyl-7-hydroxycoumarins

We have studied the particular features of the spectral and fluorescent properties of 6-isoxazolyl-7-hydroxycoumarin and its 7-methoxy-substituted analog in aprotic and proton-donor solvents of different polarity. Changes in the electron charge and bond orders in the ground and first excited states have been analyzed by the ab initio DFT and TDDFT quantum-chemical methods with the B3LYP/6–31G(d,p) basis set. Based on this analysis, we have analyzed anomalously high Stokes shifts, the shape of vibronic bands, and the fluorescence ability of these compounds in aprotic solvents. It has been found that the fluorescence spectra of hetaryl-substituted 7-hydroxycoumarin, in contrast with its absorption spectra in motional, DMSO, basic and acidic solutions, strongly differ from the fluorescence spectra of its 7-metoxy analog. We show that this is related to the proton detachment and transfer in the neutral form of 7-hydroxycoumarin upon photoexcitation with the possible formation of anion or tautomer depending on the pH of the medium.     

Spectral-luminescent properties and photoinduced transformations of bisanthene and bisanthenequinone

Based on the study of photochemical transformations of bisanthene in oxygen-containing solutions, it was established that the final product of this reaction is bisanthenequinone. It is shown that in the course of this oxidation reaction the intermediate compounds endomonoperoxide and bisanthene endobiperoxide are formed. Quantum-chemical calculation of the geometrical structure and electronic spectra of the endoperoxides has shown that they have a nonplanar structure, and their absorption spectra experience a large hypsochromic shift. The absorption and fluorescence spectra of solutions of bisanthene in different solvents at 300 and 77 K were investigated. The large Stokes shift of the fluorescence spectra of the solutions of bisanthene in benzene and in its methyl derivatives is explained by the action of intermolecular interactions. The quasi-line fluorescence spectra of solutions of bisanthene in the matrices of saturated hydrocarbons were recorded. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 176–182, March–April, 2000.     

A quantum-chemical study of the spectral and luminescent properties of photoproducts of some 8-azasteroids

The spectral and luminescent properties of photoproducts of two oxy-substituted 8-azasteroids in aprotic and proton-donor solvents are studied with the aid of methods of quantum chemistry. The electronic structure and the absorption and fluorescence spectra of isolated molecules and their complexes with water and proton hydrates are calculated and interpreted. It is shown that, orbitally, the first excited singlet state of photoproducts is close to an analogous ππ* state of 8-azasteroid. The bands observed in the absorption spectra of photoproducts are complex and are formed by two or more transitions. It is found that both neutral and charged complexes of photoproducts with water can fluoresce.     

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.     

Manifestation of enol–enol tautomerism in IR spectra of 2-acetylcyclopentanone-d<Subscript>1</Subscript>

IR spectroscopy was used to show that 2-acetylcyclopentanone (2-ACPN) exists in solutions of aprotic organic solvents as a mixture of three tautomeric forms. Assignments of absorption bands in IR spectra of 2-ACPN and its deuterated analog 2-ACPN-d₁ were made based on calculations of normal mode frequencies by a B3LYP/6-311++(2 d,2p) method for the gas phase and taking into account the influence of aprotic solvents in the framework of a polarizable continuum model (PCM). The enol–enol tautomeric equilibrium constant was evaluated for 2-ACPN-d₁ in solutions of the aprotic solvents. The content of the diketo form of 2-ACPN was shown to depend strongly on the solvent polarity and increased with it.     

Structurally Rigid 2,6-distyrylpyridines—A New Class of Fluorescent Dyes. 1. Synthesis, Steric Constitution and Spectral Properties

A group of structurally rigid analogues of 2,6-distyrylpyridine was synthesised. Molecular geometry of the synthesised dyes in solutions was studied by ¹ H-NMR, electronic absorption and fluorescence spectrometry. The spectral data testify all the compounds exist in E-configuration of their styryl residues. The most planar molecular conformation is typical for the compounds with five-membered side aromatic moieties. In the case of pyridines with six-membered aromatic residues steric hindrance results in turning the above mentioned cyclic groups out of the plane of the central pyridine moiety. The violation of planarity in this case is not significant and saves the possibility of -electronic conjugation in the molecules. The synthesised compounds are characterized by high fluorescence quantum yields in solutions. The electronic absorption spectra of titled pyridines demonstrate low sensitivity to the nature of the substituents introduced into the side aromatic rings. In contrast to this, the fluorescence bands considerably change their position under the influence of electron donor substituents. The fluorescence spectra display substantial positive solvatofluorochromism only in the cases of the dialkylamino-derivatives, especially on going from aprotic solvents to proton donor ones. Generally, the synthesised structurally rigid distyrylpyridine derivatives have prospects for their application as multi-purposes fluorescent probes.     

Fluorescence Properties and Dipole Moments of Novel Fused Thienobenzofurans. Solvent and Structural Effects

The electronic absorption, fluorescence excitation and emission spectra, and fluorescence quantum yields of novel fused thienobenzofurans, including thieno[3,2-b][1]benzofuran (1), [1]benzothieno[3,2-b]furan (2), and [1]benzothieno[3,2-b][1]benzofuran (3), were recorded in fourteen solvents of different polarities at room temperature. Compound 2 was not fluorescent. Experimental ground-state dipole moments of compounds 1–3 were measured in benzene at 298 K and compared with the corresponding theoretical dipole moment values. The solvent effects on the electronic absorption and fluorescence spectra of these thienobenzofurans were quantitatively investigated by means of solvatochromic correlations based on the Kawski-Chamma-Viallet and McRae equations. A weak negative solvatochromic behavior was found for these compounds, showing that their dipole moments are slightly lower in the excited singlet-state than in the ground-state. Kamlet-Abboud-Taft multiparameter relationships were also established for electronic absorption and fluorescence wavenumbers, and fluorescence quantum yields in most solvents, demonstrating the occurrence of specific solute-solvent interactions.     

Excited-state hydrogen bonding effect on dynamic fluorescence of coumarin 102 chromophore in solution: A time-resolved fluorescence and theoretical study

The steady-state absorption and emission as well as the time-resolved fluorescence spectra of coumarin 102 (C102) in both aprotic and alcoholic solvents have been used to study the effect of excited-state hydrogen bond on the dynamic fluorescence of C102 chromophore in various solutions. The dual fluorescence of C102 in alcohols, which is dependent on the hydrogen-bonded donation ability of the solvent, has been assigned to the distribution of free C102 and a hydrogen-bonded complex. Furthermore, a shift of the fluorescence spectra induced by excited-state hydrogen bond has been demonstrated to take place within hundreds of picoseconds by the performance of the time-resolved fluorescence spectra with the time-correlated single-photon-counting (TCSPC) technique. Moreover, the time-dependent density functional theory (TDDFT) has been used to calculate the hydrogen-bonded equilibrium constant pK_HB in different electronic states. It has been demonstrated for the first time that the hydrogen bond strengthening in electronic excited states could decrease the free energy of the hydrogen-bonded complex due to its stronger binding energy. Therefore, the hydrogen-bonded equilibrium will become markedly in favor of the hydrogen-bonded forms in electronic excited states by comparison with the case in the ground state.     

Subnanosecond spectrofluorimetry of new indolocarbazole derivatives in solutions and protein complexes and their dipole moments

The spectral and temporal characteristics of new 6,12-dimethoxyindolo[3,2-b]carbazole, 5,11-dimethyl-6,12-dimethoxyindolo[3,2-b]carbazole, and 5,11-dihexyl-6,12-di(hexyloxy)indolo[3,2-b]carbazole fluorescence probes in organic solvents and protein complexes are studied. The dipole moments of indolocarbazoles in 1,4-dioxane were measured by electrooptical absorption method. The measured dipole moments have values within the range of (3.1–3.6) × 10⁻³⁰ C m in the equilibrium ground state and increase to (4.8–5.6) × 10⁻³⁰ C m after excitation. The excited state lifetime of indolocarbazole derivatives increases with increasing polarity and viscosity of the environment. The binding of indolocarbazoles with trypsinogen and human serum albumin increases the fluorescence intensity, changes the intensity ratio of fluorescence bands, and increases the average excited state lifetime of indolocarbazoles. The analysis of the instantaneous fluorescence spectra and fluorescence decay parameters at different wavelengths revealed the existence of several types of probe binding sites in proteins. It is found that the fluorescence characteristics of indolocarbazole derivatives depend on the conformation rearrangements of trypsinogen due to its thermal denaturation.     

Molecular probe FET: Long-wavelength fluorescence excitation effect and proton transfer reaction

We studied the steady-state fluorescence spectra of solutions of FET (4′-(diethylamino)-3-hydroxyflavone) in acetonitrile that were excited at different temperatures by quanta with different energies located in the range of the main absorption band and in its long-wavelength wing. We found that, at room temperature, the emission intensity ratio of the bands of the normal and tautomeric forms, which are located at 505 and 570 nm, respectively, depends on the excitation wavelength. In the range of the main absorption band 300–360 nm, this ratio remains nearly the same, i.e., 1.45, while, upon excitation in the range of the long-wavelength wing 360–380 nm of the main band, it decreases to 1.33 at a wavelength of 460 nm. In this same range, a long-wavelength excitation effect that is unusual for liquid inviscid solvents at room temperature, i.e., a bathochromic shift of the entire short-wavelength emission band by 11 nm, manifests itself. We propose to explain these dependences using energy diagrams, which take into account the dependence of free energy on the orientational polarization of the polar solvent. The observed effect of the long-wavelength shift of the fluorescence spectrum with increasing excitation wavelength is explained in terms of the inhomogeneous broadening of electronic spectra of polar solutions, and it should be described using the scheme of energy states that takes into account sublevels of orientational broadening due to orientational dipole-dipole interactions of the fluorophore with nearest molecules of the polar solvent, as well as the relation between the fluorophore lifetime in the excited state and the dielectric relaxation time of solvent molecules in the field of the fluorophore dipole.     

Fluorescence of solutions of 8-azasteroids with α-acyl-β-aminovinyl carbonyl and imino groups

Experiments on observation of the luminescence of 8-azasteroid derivatives and its regularities are carried out for the first time. Strong solvent and excitation wavelength dependences are observed for fluorescence spectra of the compounds investigated, whereas their fluorescence excitation spectra depend only weakly on the fluorescence emission wavelength. An analysis of the data obtained points to the complex character of the electronic structure, important role of intramolecular dynamics, and multicenter character of the behavior of these systems upon absorption of light. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 315–318, May–June, 1998.     

伞形酮在不同溶剂中的荧光光谱及其二聚作用

对比研究了数种溶剂中不同浓度伞形酮溶液的荧光光谱，发现其峰形和峰位不仅随溶剂而变，且随浓度而变，据此对其发光机理进行了讨论，认为在高浓度伞形酮溶液中存在着地聚现象。二聚体的形成可以借助于与溶剂间的氢键或者单体分子间的氢键作用力来实现，浓度愈高，溶剂形成氢键的能力愈强，愈有利于二聚体的形成，二聚体激发态ＮＮ和单体激发态Ｎ都是比基态Ｎ强得多的酸。     

Fine fluorescence and absorption spectra of hypericin in a polymer matrix at a temperature of 4.2 K

Monochromatic photoexcitation and selective registration in bands of purely electronic S₁↔S₀ transitions resulted in fine fluorescence and absorption (fluorescence excitation) spectra of hypericin in polyvinylbutyral at a temperature of 4.2 K. Vibration analysis of the spectra is done and conclusions are made about the form of many normal vibrations. It is found that the formation of intramolecular hydrogen bonds in the hypericin structure has a substantial effect on the relative position of the electronic vibrational levels of the pigment molecule. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina ave., Minsk 200072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 539–545, July–August, 1998.     

Absorption and Fluorescence Emission Attributes of a Fluorescent dye: 2,3,5,6-Tetracyano-p-Hydroquinone

Four cyano groups have been substituted on the aromatic ring of p-hydroquinone (2,3,5,6-tetracyanohydroquinone) in order to study the enhanced photoacidity of this molecule. The acid-base equilibria have been studied using absorption (for ground state pK_a) and fluorescence (excited state pK_a) spectra. Three distinct species (neutral, anionic and dianionic forms) were observed in the ground state and only two species (anionic and dianionic forms) were found in the excited state when studied at different pH/H_o in water. Absorption and emission characteristics were studied in various organic solvents, including protic and aprotic solvents. Deprotonation was also investigated using binary mixtures. It has been revealed that absorption and emission spectra are considerably changed with change in media. Proton transfer to the solvent has been observed in various solvents.     

Spectrophotometric Characteristics of New Pyridylindolizine Derivatives Solutions

Three new pyridylindolizine derivatives, 1, 2, 3-tricarbometoxi-7-(4-pyridyl)-pyrrolo[1, 2-a]pyridine (I), 1,2-dicarboethoxy-3-(4-bromobenzoyl)-7-(4-pyridyl)-pyrrolo[1,2-a]pyridine (II) and its isomer 1,2-dicarboethoxy-3- (4-bromobenzoyl) -5- (2-pyridyl) -pyrrolo[1, 2-a]pyridine (III) have been investigated in different solutions by UV-VIS absorption, steady-state, and time-resolved fluorescence methods. The effects of the substituent and solvent on the spectroscopic properties have been demonstrated. The fluorescence decay data could be fitted to a single-exponential function. The lifetime values are higher in protic polar than in aprotic apolar solvents for compound I. In the case of compounds II and III the fluorescence intensities and lifetimes are very low, with the exception of III in aprotic solvents. The absorption and fluorescence properties of the compounds showed a solvent dependence.     

Electronic emission spectra ofo- andm-fluorobenzaldehyde vapours

The high resolutionnπ* electronic emission spectra ofo- andm-fluoro-benzaldehyde vapours in the region 365–560 nm excited in a discharge are reported for the first time. The spectra of both the compounds consist of theA ¹ A″ -X ¹ A′ fluorescence as well as thea ³ A″ -X ¹ A′ phosphorescence bands. In the case ofo-isomer, all the eleven out-of-plane vibrations have been observed in the fluorescence and the phosphorescence, though weakly in the latter, whereas in the case ofm-isomer, only ten have been observed in the fluorescence and nine in the phosphorescence. It is found that the most intense bands in both the fluorescence and the phosphorescence spectra of these molecules belong to the trans-O rotamer.     

Excited and ground state conformations of p-dimethylamino-benzaldehyde and p-dimethylaminoacetophenone

p-dimethylaminobenzaldehyde (DMABA) and p-dimethylaminoacetophenone (DMAA) were investigated in nonpolar and polar protic and aprotic solvents over a wide temperature range. The sequence of the lower lying excited states was established. The temperature dependence of the fluorescence yields was interpreted within the irreversible reaction kinetics scheme b¹→TICT (twisted internal charge transfer) state. The activation energies and the rate constants were evaluated. Differences between the low-temperature fluorescence or phosphorescence excitation spectra and the absorption spectrum were found to be due to the existence of different rotamers in the ground state. Quantum chemical (INDO) calculations of the energies of electronic transitions, oscillator strengths and dipole moments were performed for flat and twisted conformations of DMABA.     

Molar coefficients of extinction for IR absorption bands of Ni(II) acetylacetonate, ketoiminate, and trifluoroacetylacetonate

We have studied IR absorption spectra (within the spectral range of 4000-200 cm⁻¹ of the intracomplex chelate compounds Ni(II) bis-acetylacetonate, Ni(II) bis-ketoiminate, and Ni(II) bis-trifluoroacetylacetonate and have given a full interpretation and comparison of the spectra of these compounds in dissolved and solid states. The reasons for the differences in the spectra are discussed. The molar coefficients of extinction for the absorption bands are calculated. Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3, Akad. Lavrent’ev Ave., Novosibirsk, 630090, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 775–780, September–October, 1998.