Photophysical properties of solutions of 6,7-dimethoxy-3,4-dihydroisoquinoline

The effect of acid-base interactions on the photophysical properties of 6,7-dimethoxy-3,4-dihydroisoquinoline in protic solvents is studied by the methods of steady-state and picosecond spectroscopy. It is found that the specific features of the spectral and luminescent properties of solutions of 6,7-dimethoxy-3,4-dihydroisoquinoline are connected with the presence of emission centers of two types—solvated initial molecules and their protonated cationic forms. Considerable long-wavelength shifts observed in the electronic absorption and fluorescence spectra of the cationic form of the molecule as compared to the spectra of its initial form are caused by the elongation of a conjugated chain present in the fragment of the molecule that separates the nitrogen atom and the oxygen atoms of the methoxy groups. The transition of the cationic form of the molecule to an excited electronic state is not accompanied by a change in its dipole moment.     

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.     

Modulation of the proton transfer rate by excitation photons

The effect of the exciting photon energy on the excited state proton transfer in a dye with dual fluorescence—FET (4′-diethylamino)-3-hydroxyflavone)—is studied. The steady-state fluorescence spectra are studied upon selective excitation by photons with different energies in the region of the main absorption band, as well as at its long-wavelength wing, in the temperature range of 2–30°C. It is found that, at all temperatures, the ratio of the integral emission of the normal and tautomeric forms, which are observed at 480 and 570 nm, respectively, depends on the excitation wavelength; namely, this ratio noticeably decreases with increasing excitation wavelength in the region of the main absorption band and its long-wavelength wing at 390–440 nm, and the rate of this decrease depends on temperature. In the same region, the long-wavelength excitation effect, which is atypical for inviscid solvents at room temperature, is observed; i.e., a short-wavelength emission band is bathochromically shifted by 6–15 nm depending on temperature. This spectral shift is directly related to the inhomogeneous broadening of the electronic spectra of the normal FET form, which is very large due to a considerable (>10 D) difference in the dye dipole moments. Most probably, the excitation creates the possibility of emission from nonrelaxed nonequilibrium orientational sublevels because their lifetime becomes shorter due to the proton transfer reaction, the rate of which in acetonitrile is comparable with the rate of intermolecular orientational relaxation. It is proposed to explain these dependences using energy diagram taking into account the dependence of the free energy on the orientational polarization of the solvent.     

Spectral properties of anionic form of 3-hydroxyflavone

The spectral and temporal characteristics of the fluorescence of the anionic form of some 3-hydroxiflavones in different solvents are studied. This form is observed under selective excitation in the region of the long-wavelength slope of the main absorption band, and its spectrum consists of a wide structureless band lying between the short- and long-wavelength fluorescence bands of these molecular probes. The fluorescence excitation spectra of the anionic form differ from the corresponding spectra of the normal and tautomeric forms. The addition of water to the solution leads to a gradual fluorescence quenching which is static or belongs to the second kind according to Vavilov’s classification, i.e., occurs in the ground state.     

Polymorphism and Intramolecular Proton Transfer in Fluoroquinolone Compounds

Electronic absorption, luminescence, IR and Raman spectra of polymorphous forms of fluoroquinolones were investigated. Assignment of the band maxima due to π→π* and n→π* electronic transitions were done. The structural changes are responsible for the absorption band modifications. One-electron transitions in the long wavelength region, excitation wavelengths, oscillator strengths and involved molecular orbitals for the zwitter-ionic and cationic protonated forms for different fluoroquinolones were calculated with quantum-chemical and molecular dynamic methods. The electron density redistributions on the FQs separate fragments during the photoexcitation to the S₁*-state were carry out by Mulliken calculations. It was shown that the degree of neutral and zwitter-ion FQs penetration through the bacterium membrane is different.     

Zum Konzept der charakteristischen Intensitäten der Resonanz-Ramanlinien von Azofarbstoffen

The resonance Raman spectra of the solutions of some azobenzene and hydroxyazonaphthalene compounds were investigated. The relative corrected scattering coefficientsS of the lines have been measured. Assuming the existence of a characteristic intensity, the frequency dependence and the influence of data of the long-wavelength electronic absorption band has been discussed. Testing formulas for intensity dependence in this way it has been shown, that they cannot exactly describe resonance Raman intensities, because there is the problem of the “effective” electronic absorption band. This was studied by comparison of the intensities of several azonaphthalene lines, excited by the mercury lines 4358 and 5461 Å.     

On the mechanism of formation and broadening of the electronic and vibrational spectra of vapors of octaethylporphyrin metal complexes

Optical absorption spectra of vapors of metal complexes of octaethylporphyrins known from the literature are analyzed on the basis of notions about sequences as basic elements of the formation of electronic-vibrational bands. According to this analysis, major features of these spectra are explained. These features include considerable half-widths of the electronic-vibrational bands of rarefied vapors, when intermolecular interactions virtually do not affect the broadening; a Lorentzian intensity distribution over the contour of the 0-0 spectral band; long-wavelength shifts of the intensity maxima of bands with increasing temperature; and the origin of a fine structure of the electronic and vibrational spectra at low temperatures. It was concluded that sequential transitions form the basis of the mechanism of formation and broadening of the electronic and vibrational spectra of metal complexes of octaethylporphyrins as representatives of complex biomolecules.     

Surface-enhanced Raman spectroscopy of morphine in silver colloid

We report the surface-enhanced Raman （SERS） spectra of morphine in silver colloid, and study the silver colloid enhanced effects on the Raman scattering of morphine. The Raman bands of morphine are assigned to certain molecule vibrations. The broad band in the long-wavelength region of the electronic absorption spectra of the sol with added adsorbent at certain concentrations has been explained in terms of the ag- gregation of the colloidal silver particles. The potential applications of SERS in quantitative measurement of the morphine samples are demonstrated. By using a proper Raman band of morphine, the detection limit of morphine in silver sol is found to be 1.5 ng/ml. The result suggests that it is of great significance to use SERS in illicit drug morphine inspection.     

Electronic absorption spectra of antiviral aminophenol derivatives

Electronic absorption spectra of aminophenol derivatives in solutions have been studied. A general property of the absorption spectra of these compounds, the dependence of the maximum of a long-wavelength absorption band on the solvent polarity, is revealed. As a rule, the absorption band maximum of compounds possessing pharmacological properties shows a greater shift to short wavelength with an increase in the medium polarity than that of inactive compounds. Absorption measurements of solutions of aminophenol derivatives can be used for a tentative estimation of their antiviral activity.     

Nonradiative energy transfer in a concentrated solution of prodan

The temporal characteristics of luminescence decay in concentrated solutions of prodan excited by picosecond laser radiation are studied The electronic spectra exhibit a strong inhomogeneity, which, in the case of elevated solution viscosity, manifests itself under steady-state conditions of measurements. The temporal characteristics of the luminescence decay and the time-resolved luminescence spectra point to the occurrence of relaxation processes causing a long-wavelength shift of the emission band with time. An increase in the prodan concentration from 10^?4 to 5 × 10^?2 M leads to a faster increase in the luminescence lifetime in the long-wavelength spectral region and to a higher rate of shifting of the instantaneous spectra, which is related to energy transfer over the states of inhomogeneous broadening of the luminophore.     

Solution electronic spectra of brassinosteroid and a synthesized conjugate of a steroid and a fluorescent label

Electronic absorption spectra of 24-epicastasterone and 24-epibrassinolide solutions have been recorded and analyzed. The long-wavelength band in solution spectra of the former steroid with maxima in the region 292–286 nm is assigned to the electronic nπ*-transition of a carbonyl chromophore. The latter steroid contains an O-C=O group, for which the extinction coefficient in this spectral region is approximately one order of magnitude less. These differences can be used to identify the studied steroids. A method to synthesize the conjugate of 24-epicastasterone with a fluorescent label, dansylhydrazine, which shows intense fluorescence and absorption, is described. Absorption spectra of the label and conjugate in diethylether, tetrahydrofuran, ethanol, and acetonitrile solutions are practically independent of the solvent properties. The exceptions are solutions of the conjugate in hexane and water. All investigated solutions of label and conjugate show intense fluorescence. As the dielectric constant of the solvent increases, the fluorescence spectra shift to long-wavelength. The fluorescence energetic and time characteristics of both the label and conjugate are similar, which enables the conjugate to be used in developing a method for immunofluorescent analysis of the brassinosteroid 24-epicastasterone. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 74–78, January–February, 2008.     

Electronic structure and spectral and luminescent properties of anti-HIV-active aminophenols

The method of intermediate neglect of differential overlap (INDO) with spectroscopic parameterization is used to calculate the electronic structure and the electronically excited states of substituted o-aminophenols comprising the SO₂ group. It is demonstrated that incorporation of this group into the 2-anilino-4,6-di-tretbutylphenol molecule leads to separation of the π-systems of phenyl rings forming the molecule. The intramolecular hydrogen bonds of various types and the SO₂ group change the charge redistribution between separate fragments of molecules thereby decreasing the donor properties of the phenyl fragments and the acceptor properties of the hydroxyl and amino groups. The influence of the SO₂ group on the absorption and fluorescence spectra is insignificant and consists in a small long-wavelength shift of the absorption band spectrum and insignificant changes of the band intensities. Due to a higher degree of deviation of the molecules from the planar structure after incorporation of this group, the intersystem crossing increases; therefore, the quantum fluorescence yield of sulfosubstitutes is insignificant.     

Substituent Effects on Electronic Spectra of Vicinally Substituted 2-, 3- and 4-Aminopyridines

The electronic spectra of forty vicinally substituted 2-, 3- and 4-aminopyridines have been discussed. The low-energy transition of 17 derivatives was analyzed with the help of CNDO/S calculations. In general, the experimental band corresponds to two theoretical transitions. The dual substituent parameter approach (DSP) quite well explains the frequency of one transition in the long-wavelength region of the experimental spectrum.     

[M(SS)(NN)](M=Zn2+,Cd2+)配合物分子内跃迁与结构的关系

报道了配合物[M(SS)(NN)](M=Zn2 ,Cd2 )(SS=mnt2-,1,2-二氰基乙烯-1,2-二硫醇离子,NN=5-NO2-phen,5-硝基-1,10-邻菲咯啉)的合成,探讨了Zn(SS)(NN)和Cd(SS)(NN)在二甲基亚砜(DM-SO)、二甲基甲酰胺(DMF)、丙酮(acetone)、吡啶(Py)等溶剂中的电子吸收光谱。研究发现配合物的紫外区的吸收带270～280nm,320～350nm,350～390nm本质上属于配体mnt2-,5-NO2-phen内部的πb→π*跃迁,可见光区400～500nm本质上属于配体mnt2-到配体5-NO2-phen的荷移跃迁(LL′CT)。确认了标题配合物的荷移跃迁光谱在相关分子轨道能级图中的对应关系。标题配合物的LL′CT吸收带与组成相似配合物M(SS)(NN)(M=Co2 ,Fe2 ,Ni2 ,Cu2 )的对应吸收带相比较弱一些,这是由于[M(SS)(NN)](M=Zn2 ,Cd2 )的LL′CT谱带(7b2→7b1)是部分解除轨道禁阻的跃迁。     

Resonance states of gallium impurity in uniaxially compressed germanium

To identify optical transitions that can excite long-wavelength stimulated radiation in uniaxially compressed Ga-doped germanium, the absorption and photoconduction spectra of this material were studied over a wide range of pressures in the [111] and [001] directions. It was found that some of the excited states of gallium impurity became resonant upon the buildup of pressure. The energy levels of these states reach the light-hole band, whereupon they enter this band and remain near its edge, showing up in the form of broad bands. No singularities confirming the existence of the impurity resonance states were observed in the spectra near the edge of the heavy-hole band.     

Anisotropy of optical absorption and luminescent properties of CaMoO4

Optical absorption, excitation and emission spectra, as well as photoluminescence decay time of CaMoO₄ single crystals have been measured. It has been revealed that annealing of crystals in oxygen atmosphere leads to the disappearance of their anisotropic behavior in optical absorption, as well as in X-ray luminescence and decay time. Moreover, it has been found that annealing can significantly affect the value of the decay time. The relative intensity of the long-wavelength emission band increases under excitation in the region of indirect band-to-band transitions.     

Singlet-triplet transitions in substituted benzenes containing OH and NH2 groups

The electronic absorption spectra of substituted benzenes containing OH and NH₂ groups are investigated in the 2500–5000 Å region. It is shown that the absorption band in the long-wave region is a singlet triplet absorption band.     

Conformers and Electronic Spectra of Dansylamide: Experimental and Theoretical Studies

Particular features of the geometrical and electronic structure of six possible conformers of dansylamide ((CH₃)₂N–C₁₀H₆–SO₂NH₂) are considered. The electronic absorption spectra of the conformers of dansylamide in the free state and taking into account the influence of an aqueous solvent (in terms of the PCM model) are calculated by the TDDFT method. It is shown that, as a result of taking into account solvation, the electronic absorption spectra of the conformers exhibit a bathochromic shift, and the difference in the values of λ of the conformers reaches 16 nm. The calculated electronic absorption spectra in an aqueous medium agree qualitatively with the obtained experimental spectra. An analysis of molecular orbitals involved in the first three electronic transitions of the conformers is carried out. It is suggested that the broadening of the band with λ_max = 326 nm in the experimental spectrum may be caused by the presence of dansylamide conformers in the aqueous solution. It is shown that the calculated values of λ in the electronic absorption spectra of dansylamide in the aqueous solvent depend substantially on the DFT functional type.     

Study of spectral properties of zinc phthalocyanines used as sensitizers in photodynamic therapy

Some features of the influence of the structure of water-soluble zinc phthalocyanines on their spectral parameters and state in solutions are studied. It is shown that the position of the long-wavelength electronic absorption band only weakly depends on the type of ionogen substituents in the zinc phthalocyanine macrocycle. It is found that the state of the dye in aqueous solution substantially depends on the type of a substituent in the dye macrocycle.     

Intermolecular Hydrogen Bonding and Proton Transfer in the Ground and Lowest Excited Singlet States of the Ethyl Esters of 1- and 2-naphthoic Acid

The absorption spectra of ethyl 1-naphthoate in hexane and in water demonstrate normal dependences upon solvent hydrogen bonding and polarity properties while the absorption spectra of 1-naphthoic acid do not. This is attributed to inhibition of conjugation by steric interference between the carbethoxy group of the ester or the hydrated carboxyl group of the acid and the peri-hydrogen atom of the naphthalene ring in the 5-position, in the ground electronic state. The anomalous fluorimetric titration characteristics of the 1- and 2- naphthoic esters and of 1-naphthoic acid are attributed to hydrogen bonded exciplex formation in the lowest excited singlet state.

In a recent study of the solvent and acidity dependences of the electronic absorption and fluorescence spectra of 1- and 2-naphthoic acid (1) several phenomena were observed which were rather unusual and whose explanations were beyond the scope of the previous study. Among these were 1) the red shift of the absorption spectra upon going from water to hexane media and 2) the destruction of the conjugate relationship between the excited acidium cations and neutral molecules of the 1-isomer as evidenced by the fluorimetric titrations of these species occurring in different pH regions In order to more closely examine these phenomena and perhaps to explain them in terms of the interactions of the protonated and neutral car box y groups with the solvent and the naphthalene ring, the present study of the lectronic absorption and fluorescence spectra of the ethyl esters of 1- and 2-naphthoic acid was undertaken.