Investigations into the spectral and luminescent properties of methylphenols in neutral and ionic forms in aqueous micelle solutions

The special features of the absorption and fluorescence spectra of some substituted phenols (2-, 4-methylphenol and 2-amino-4-methylphenol) in aqueous micelle solutions are investigated on addition of an alkali and acid. A fluorescence band of 4-methylphenol in the anion form is detected in the presence of a cation surfactant. The fluorescence efficiency of 4-methylphenol in the presence of the triton X100 micelle decreases in comparison with aqueous solutions. It is established that the quantum yield of fluorescence of 2-methylphenol in the presence of N-cetyltrimethyl ammonium bromide (CTAB) increases in comparison with the aqueous solution (ϕ_fl = 0.25 and 0.17, respectively). The constant of fluorescence quenching for methylphenol in aqueous micelle solutions by the alkali is two orders of magnitude higher than by the acid. The proton-acceptor properties of 2-amino-4-methylphenol are higher than of 4-methylphenol. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 54–61, November, 2005.     

Photoconversion of 2-methylphenol, 4-methylphenol, and 2-amino-4-methylphenol in water

We have used fluorescence spectroscopy to study photoconversions of 2-methylphenol (2-MP), 4-methylphenol (4-MP), and 2-amino-4-methylphenol (2-A-4-MP) in water when excited by UV radiation from different sources. We discuss the effect of the acidity of the medium and dissolved oxygen on photoconversions of the indicated methylphenols. The photodegradation efficiency for 2-MP and 4-MP decreases in the absence of oxygen. The photoconversion efficiency for methylphenols in alkaline medium is higher when irradiated by light with λ_rad = 283 nm, while in neutral medium it is higher when irradiated by light with λ_rad = 222 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 566–572, September–October, 2006.     

Synthesis of a New Thermal and Photostable Reference Probe for Qf Measurement in Aqua: Water Soluble N,N′-bis-(2-Hydroxy-4-benzoic Acid)-3,4,9,10-perylenebis(dicarboximide)

N,N′-bis(2-hydroxy-4-benzoic acid)-3,4,9,10-perylenebis(dicarboximide) is synthesized from perylene 3,4,9,10-tetracarboxylic dianhydride and 4-amino-3-hydroxy benzoic acid in 90% yield. Together with the photostability the dye is also very stable thermally. The fluorescence quantum yield is measured as one, Q_f=1.The diimide dissolves in water at PH = 8 completely. The diimide is an ideal reference probe for fluorescence quantum yield measurements in 500–650 nm region and an attractive photosensitizer for the photoreactions occur in water.     

Photophysical properties, laser activity and photoreactivity of a heteroaryl chalcone: A model of solvatochromic fluorophore

The absorption and fluorescence characteristics of 3-(4′-dimethylaminophenyl)-1-(2-thienyl)prop-2-en-1-one (DMATP) have been investigated in different solvents. DMATP dye exhibits a large red shift in both absorption and emission spectra as solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. A crystalline solid of DMATP gave an excimer like emission at 570 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. A dye solution ca. 10⁻³ mol dm⁻³ in CHCl₃ gave a good laser emission in the range 480–560 nm with emission maximum at 530 nm upon pumping by nitrogen laser (λ_ex=337.1 nm). The excitation energy transfer from 7-dimethylamino-4-methyl coumarine (DMC) to DMATP has been also studied in CHCl₃ and the values of energy transfer rate constant and critical transfer distance indicate a Főrster-type mechanism. The photoreactivity and net photochemical quantum yield of DMATP in chloromethane solvents are also determined. We applied semiempirical MO calculation using AMI and ZINO/S calculation to understand the geometric and electronic structure of DMATP molecule in both ground and excited states.     

Special Features of Quenching of Fluorescence in the 1-Naphthol and Coumarin 1 Molecules in Binary Mixtures

The work studies the effect of intermolecular interactions on the relation between the rate constants of radiative processes and internal intercombination conversion in particlular molecule - solvent systems. The 1-naphthol complexes in binary mixtures with hydrogen bonding and those of coumarin 1 with nitrogen-nitrogen bonding are examined. The Stern - Volmer curves for the complexes with additions of nitromethane are shown to deviate from linearity.The interaction of coumarin 1 and 1-naphthol with nitromethane was simulated by the INDO/SP method to show that the lower singlet state is associated with nitromethane. The experimentally observed fluorescence band of the coumarin 1 and 1-naphthol molecules belongs to the third singlet state. The quantum yield of fluorescence from the S₃ state is decreased by an order of magnitude for the complexes under study. The quantum yield from the lower singlet state in the 1-naphthol - nitromethane complex is decreased by an order of magnitude, while in the coumarin 1 - nitromethane complex - by two orders. It is found that there is a possibility of photoprotonation in the S₁ and S₂ states for the 1-naphthol molecule along with the foregoing processes of quenching of fluorescence.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 17–23, January, 2005.     

A new coumarin laser dye 3-(benzothiazol-2-yl)-7-hydroxycoumarin

The electronic absorption, and emission spectra as well as fluorescence quantum yield of 3-(benzothiazol-2-yl)-7-hydroxycoumarin (BTHC) were measured in different solvents and are affected by solvent polarity (Δf). The deprotonation of BTHC by triethylamine is a reversible process. BTHC is relatively photostable, the quantum yield of photodecomposition (φ_c) was found to be 2×10⁻⁴ and 2.7×10⁻⁴ in EtOH and DMF, respectively. The fluorescence lifetimes of BTHC were measured in the absence and in the presence of molecular oxygen and were found to be 2.82 and 2.78 ns, respectively. BTHC acts as good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in ethanol and gives laser emission with maxima at 508 and 522 nm.     

Sub-poissonian statistics of fluorescence photons of a single molecule

The method previously used by the author for the measurement and calculation of the distribution function w _N(T)of fluorescence photons from a single two-level atom that is continuously excited by laser light and has a unity fluorescence quantum yield is generalized to the case of a single molecule whose fluorescence quantum yield is smaller than unity and to the case of a three-level molecule whose fluorescence is blinking. The functions w _N(T) calculated for these two cases demonstrate a sub-Poissonian distribution of fluorescence photons.     

Complexing and photoprocesses in a PRODAN molecule

The effect of hydrogen bond on the spectral-luminescent properties of the PRODAN molecule — water complexes is studied. Quantum chemical calculations are performed for the ground and fluorescent equilibrium states of a free PRODAN molecule and its complexes with H₃O⁺. It is shown that significant changes occur in the geometry of the molecule in the fluorescent state. To describe the fluorescent state, account was taken of the changes in the electron density (population) on the bonds and atoms in transition of the molecule to an excited state. The rate constants of radiative and nonradiative processes and quantum yields of fluorescence are calculated for the PRODAN molecule and its complexes in water. A significant shift of the fluorescent bands (sensitivity to a solvent) in transition of the molecule from cyclohexane to water is accounted for.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 71–75, November, 2004     

Proton-acceptor and proton-donor properties of phenol and its substitutes

The donor-acceptor ability of phenols (phenol, 4-chlorphenol, 4-methylphenol, 4-bromphenol, hydroquinone, 4-methyl, and 2-aminophenol) and their complexes with water are investigated by the quantum-chemical method. Incorporation of NH₂ and CH₃ substitutes in the phenol molecule leads to the intensification of the electron density transfer on the carbon atoms of the aromatic ring. The formation of the planar complex increases, and the formation of the nonplanar complex, on the contrary, decreases the proton-acceptor ability of phenols in the ground state. The formation of the nonplanar complex leads to an increase in the proton-donor properties of phenols under excitation. The incorporation of the chlorine atom into the para-position results in the dependence of the donor-acceptor properties of the molecule on the excitation energy. The incorporation of OH-and CH₃-groups in para-position does not influence the proton-donor properties of the isolated phenol molecule. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 28–33, December, 2005.     

Fluorescence quantum yield of carbon dioxide for quantitative UV laser-induced fluorescence in high-pressure flames

The fluorescence quantum yield for ultraviolet laser-induced fluorescence of CO₂ is determined for selected excitation wavelengths in the range 215–250 nm. Wavelength-resolved laser-induced fluorescence (LIF) spectra of CO₂, NO, and O₂ are measured in the burned gases of a laminar CH₄/air flame (φ=0.9 and 1.1) at 20 bar with additional NO seeded into the flow. The fluorescence spectra are fit to determine the relative contribution of the three species to infer an estimate of fluorescence quantum yield for CO₂ that ranges from 2–8×10^?6 depending on temperature and excitation wavelength with an estimated uncertainty of ±0.5×10^?6. The CO₂ fluorescence signal increases linearly with gas pressure for flames with constant CO₂ mole fraction for the 10 to 60 bar range, indicating that collisional quenching is not an important contributor to the CO₂ fluorescence quantum yield. Spectral simulation calculations are used to choose two wavelengths for excitation of CO₂, 239.34 and 242.14 nm, which minimize interference from LIF of NO and O₂. Quantitative LIF images of CO₂ are demonstrated using these two excitation wavelengths and the measured fluorescence quantum yield.     

Purine Scaffold Effect on Fluorescence Properties of Purine-Hydroxyquinolinone Bisheterocycles

The fluorescence properties of bisheterocyclic compounds that contain purine and the 3-hydroxyquinolin-4(1H)-one skeleton connected with an aliphatic spacer of a different length/structure (3HQP) were examined. It was found that the introducing of the spacer-purine scaffold led in the comparison to 3HQs themselves to (1) the possibility of the effectual excitation in the wider range of excitation wavelengths, moreover, some derivatives can be excited at relatively high wavelengths around 400 nm, (2) the lowering of the quantum yield and (3) the slight longer wavelength shift of the dual emission spectra. Tested organic solvents did not affect significantly the 3HQP fluorescence properties. The characters of emission spectra as well as the quantum yields of 3HQPs were notably influenced by the ratio of water and DMSO in their composed mixture applied as a solvent. With increasing water content in the mixture both I₁/I₂ and the quantum yield decreased.     

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.     

Spectral behavior study of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone

The photophysical properties such as singlet absorption, molar absorptivity, fluorescence spectra, fluorescence quantum yield (?_f) and transition dipole moment (μ₁₂) of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone (DMAPAPP) have been studied in different media. DMAPAPP exhibits a large red-shift in both absorption and emission spectra as the solvent polarity increases, indicating a large change in dipole moment of molecule upon excitation. The fluorescence quantum yield depends on the nature of the solvent. The absorption and emission spectra of DMAPAPP in dioxane–water mixture are also studied. The effect of different type of surfactants to determine their critical micellar concentration (CMC) and the microemulsion effect on the electronic absorption and emission spectra of DMAPAPP are recorded. The effect of acidity on the electronic absorption and emission spectra of DMAPAPP is studied to determine the pK_a and pK_a^? values.     

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10⁻³ mol dm⁻³ of DEAC gives laser emission in the blue region on pumping with nitrogen laser (λ_ex=337.1 nm). The laser parameters such as tuning range, gain coefficient (α), emission cross section (σ_e), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl₄ at a wavelength of 366 nm. The values of photochemical yield (?_c) and rate constant (k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH₃CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.     

Spectral-luminescent properties of chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> and malate dehydrogenase complexes

Spectral confirmation of the formation of stable equilibrium complexes (association constant K _as = 210⁶ M^–1) of the Krebs cycle enzyme — malate dehydrogenase (MDH) — and one of the promising photodynamic sensitizers — chlorin e ₆ — have been obtained. It is shown that the incorporation of dye molecules into the protein globule of dimeric MDH (each subunit of which contains 4 tryptophan amino acid residues, each binding one molecule of chlorin e ₆) is accompanied by quenching of the tryptophan fluorescence of the enzyme. However, despite the overlapping of the fluorescence spectra of tryptophanyls of MDH and the absorption spectrum of chlorin e ₆, the fluorescence quenching observed is not caused by singlet-singlet inductive-resonant transfer of energy from the donor to the acceptor. The conclusion has been drawn that the reason for the absence of energy transfer from tryptophanyls to the dye is the more effective intertryptophan migration of energy to one of the most longwave amino acid residues, the quenching of the luminescence of which occurs due to the reversible photoinduced transfer of an electron to chlorin e ₆ (formation of a complex with charge transfer). The formation of a complex with charge transfer between chlorin e ₆ (when it is excited) and one of the amino acid residues of the enzyme that contact with the dye at its binding site on the protein molecule is also the most noncontradictory explanation of the observed (when bound with MDH) decrease in the quantum yield of fluorescence of chlorin e ₆ upon increase in the duration of its quenching. The question of the ability of MDH to act as one of the most sensitive targets responsible for the disturbance of mitochondrial functions and initiation of the apoptosis of tumor cells in the process of photodynamic therapy is discussed.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 749–758, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Measurement of Fluorescence Quantum Yield of Ultraviolet-Absorbing Substance Extracted from Red Alga: Porphyra yezoensis and its Photothermal Spectroscopy

Optical properties of an ultraviolet-absorbing substance (UVAS) extracted from the marine red alga, Porphyra yezoensis, have been investigated. The substance is excited by UV light, and the emitted fluorescence is detected using an intelligent fluorescence detector. The fluorescence of UVAS is weaker by four orders of magnitude than the fluorescence intensity emitted by anthracene in the same optical system. The absorbed energy is apparently not transferred to the photosynthesis process and is believed to be consumed as heat. Using photothermal spectroscopy, a signal is observed indicating that the absorbed photon energy has transferred to the heat. The waveform of the photothermal signal of UVAS is similar to that of quinoxaline, whose fluorescence quantum yield is known to be zero. It is determined that the fluorescence quantum yield and the energy of the triplet state of UVAS are 1.7 ± 0.7 ± 10⁻⁴ and 21000 ± 1000 cm ⁻¹, respectively. The conclusion is that the excited molecules of UVAS decay by passing through the triplet state and dissipate all absorbed energy as heat.     

Absorptivity and fluorescence properties of 9,10-diiodoanthracene in solutions

The molar extinction coefficient, oscillator strength, natural fluorescence lifetime, and fluorescence quantum yield have been determined for 9,10-diiodoanthracene in ethanol at 20°C. The temperature effect on the quantum yield was studied in the range 120–300 K. The fluorescence lifetime was measured at 77 K. During glassification of ethanol, the fluorescence intensity of 9,10-diiodoanthracene increases by more than 50 times due to the activation nature of the intersystem crossing from the S₁(¹B_2u⁺) state. The activation energy and pre-exponential factor for the probability of the intersystem {ie319-01}-crossing are found. The long-wavelength shift of the absorption spectrum with increasing bulk polarizability of the solvent is interpreted as evidence of changes in the nonspecific interactions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 304–308, May–June, 2008.     

Spectral-Luminescent Properties of Neutral and Ionic Cresols

The spectral characteristics of various forms (neutral, anionic, and cationic) of o- and p-cresols in water have been investigated by electron-absorption spectroscopy, fluorescence, and quantum-chemistry methods. The presence of a methyl substituent in cresol in the orthostate enhances the acid and base properties of this substance in the excited state as compared to those of cresol in the parastate. The difference between the mechanisms of formation of cationic o- and p-cresols is explained by the inversion of electron levels in the system of electron-excited states. Ionic cresols have a low quantum yield of fluorescence (≤10⁻²) because the efficiency of intercombination conversion in them is higher as compared to that of neutral cresols.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 165–170, March–April, 2005.     

Quantum-Chemical Calculations of the Excited Electronic States of the Prodan Molecule and Its Complexes in Water

A quantum-chemical calculation of the prodan molecule and its complexes in water for the geometry of the ground and fluorescent states is carried out. To describe the fluorescent state, changes in the electronic state (population) on bonds and atoms during transition of the molecule into an excited state are taken into account. A model of interaction of the prodan molecule with a polar proton-donor solvent (water) is suggested. It is shown that interaction with the ionic forms (H₃O₊ provides an explanation for the sensitivity of prodan to the solvent (displacement of the fluorescence bands). The nature of the electronic excited states of the prodan molecule and its complexes has been investigated. The constants of the rates of radiative and nonradiative processes and the fluorescence quantum yields have been calculated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 330–334, May–June, 2005.     

Preparation,Characterization and Application of Fluorescent Terbium Complex-Doped Zirconia Nanoparticles

Novel zirconia-based fluorescent terbium nanoparticles have been prepared as a fluorescent nanoprobe for time-resolved fluorescence bioassay. The nanoparticles were prepared in a water-in-oil (W/O) microemulsion consisting of a strongly fluorescent Tb³⁺ complex, N,N,N¹, N¹-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-phenylpyridine]tetrakis(acetate)-Tb³⁺(BPTA-Tb³⁺), Triton X-100, hexanol, and cyclohexane by controlling co-condensation of Zr(OCH₂CH₃)₄ and ZrOCl_2. The characterizations by transmission electron microscopy and fluorometric methods indicate that the nanoparticles are uniform in size, 33± 4 nm in diameter, and have a fluorescence quantum yield of 8.9% and a long fluorescence lifetime of 2.0 ms. The zirconia-based fluorescent terbium nanoparticles show high stability against basic dissolution in a high pH aqueous buffer compared to the silica-based nanoparticles. A surface modification and bioconjugation method for the fluorescent nanoparticles was developed, and the nanoparticle-conjugated streptavidin (SA) was used for time-resolved floroimmunoassy (TR-FIA) of human prostate specific antigen (PSA). The result shows that the zirconia-based fluorescent terbium nanoparticles are useful as a fluorescent nanoprobe for time-resolved fluorescence bioassay.