Optical characterization of sol gel TiO<Subscript>2</Subscript> monoliths doped with Brilliant Green

Amorphous titanium dioxide monoliths doped with brilliant green (BG) were synthesized by the sol-gel process. The optical properties of the monoliths were characterized by Photoacoustic Spectroscopy and Photoluminescence Spectroscopy. The absorption spectra for the BG-doped TiO₂ monoliths exhibited two well defined absorption regions: a band below 400 nm corresponding to TiO₂ absorption and three absorption bands centered at 424 nm, 588 nm, and 632 nm due to brilliant green. While the undoped TiO₂ monoliths showed no luminescence, the doped samples showed a strong luminescence band at 673 nm, which increased its intensity for increasing organic dye doping.     

Fluorescence and electrochemical recognition of nucleosides and DNA by a novel luminescent bioprobe Eu(III)-TNB

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs –ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A method is presented for determination of nucleosides using the effect of enhancement of fluorescence of the easily accessible europium(III)-TNB in presence of different nucleosides. The latter coordinates to Eu(III) -TNB and enhances its luminescence intensity as a result of the displacement of water from the inner coordination sphere of the central metal. A similar method for the determination of DNA based on the quenching of Eu(III)-TNB has been established. The interaction of Eu(III)-4,4,4 trifluoro-1-(2-naphthyl)1,3-butanedione (TNB) complex with nucleosides (NS) (guanosine, adenosine, cytidine , inosine) and DNA has been studied using normal and time-resolved luminescence techniques. Binding constants were determined at 293 K, 298 K, 303 K, 308 K and 313 K by using Benesi-Hildebrand equation. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. The formation of binary and ternary complexes of Eu (III) with nucleosides and TNB has been studied potentiometrically at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol.dm⁻³ (KNO₃) . The formation of the 1:1 binary and 1:1:1 ternary complexes are inferred from the corresponding titration curves. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the HYPERQUAD computer program. Electrochemical investigations for the systems under investigations have been carried out using cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon electrode in I = 0.1 mol/L p-toluenesulfonate as supporting electrolyte.     

Control of optical properties of polymethine dye <Emphasis Type="Italic">J</Emphasis>-aggregates using different additives

The effect of various additives (NaCl, DNA, and CPB surfactant) on the structure and optical properties of luminescent molecular nanoclusters, J-aggregates of L-21 polymethine dye, has been investigated using stationary and time-resolved optical spectroscopy. It has been shown that all investigated additives enhance the dye aggregation and change its aggregate structure as manifested in a change of tilt angle between molecules in the molecular chain. Salt causes the biggest change of tilt angle whereas surfactant causes the smallest. It has been found that a decrease of tilt angle leads to an increase of J-aggregate luminescence intensity. The addition of CPB surfactant is shown to modify the exciton dynamics in J-aggregates whereas the other additives affect only their structure. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 250–255, March–April, 2009.     

Photophysical Characterization of New 3-Amino and 3-Acetamido BODIPY Dyes with Solvent Sensitive Properties

The structural, electronic and photophysical properties of three new asymmetric, highly fluorescent difluoroborondipyrromethene (BODIPY) dyes, bearing an amino or an acetamido group at position 3 of the chromophoric core, have been studied in different apolar, polar and polar/protic solvents. The presence of the 3-amido group extents the delocalization of the π-system, leading to bathochromic shifts in the absorption and fluorescence bands, as predicted by quantum mechanic calculations. The 3-amino dye shows photophysical properties highly dependent on the solvent polarity and acidity, and is characterized by a hypsochromic shift of its absorption band, with regard to the corresponding acetylated dye, as well as a low fluorescence quantum yield in acid media with proton concentration lower than 4 × 10⁻⁴ M. In media with higher proton concentration, the BF₂ bridge group of the 3-amino dye is removed, yielding the corresponding non-fluorescent dipyrromethene precursor. These results suggest that the 3-amino dye could be used as a fluorescence probe for the study of the acidity of different environments.     

Spectroscopic properties of DNA-acridine orange biopolymer films

Using electronic absorption, luminescence, and vibrational spectroscopy, we study the properties of DNA-acridine orange biopolymer films. The conformational structure of DNA molecules in the film is examined at different levels of the relative humidity, and the state of dye molecules incorporated into the structure of the biopolymer is estimated. These structures were formed according to the “guest-host” principle and the dye molecule acts as the “guest” and the “host” is the intercalative DNA binding sites. In such system dye molecules demonstrate high luminescence capability and are the uniform optical centers and their fluorescence spectrum doesn’t depend on excitation wavelength.     

The effect of electron irradiation on the optical properties of the natural armenian zeolite-clinoptilolite

Infrared (IR) absorption and luminescence in chemically and radiation-modified natural Armenian Zeolite (clinoptilolite) samples have been studied. The luminescence was studied in 390–450 nm and 620–710 nm wavelength bands, and the IR measurements were carried out in the 400–5400 cm⁻¹ range. It is shown that the luminescence intensity depends on the content of pure clinoptilolite in the samples and, probably on the distribution of “passive” luminescence centers over Si and Al sites that became “active” under radiation or chemical treatment. The samples of electron irradiated clinoptilolite have higher luminescence intensity than the chemically and thermally treated ones. A decrease in the intensity of IR absorption bands at 3550 cm⁻¹ and 3650 cm⁻¹ was found after irradiation.     

Multifunctional Er3+–Yb3+ codoped Gd2O3 nanocrystalline phosphor synthesized through optimized combustion route

This paper reports the synthesis of high upconversion luminescent Gd₂O₃: Er³⁺, Yb³⁺ nanophosphor through optimized combustion route using urea as a reducing agent. The paper also reports the first observation of upconversion emission bands extending upto the UV region (335, 366 and 380 nm) in Er³⁺–Yb³⁺ co-doped phosphor materials. The fuel to oxidizer ratio has been varied to obtain the maximum upconversion luminescence. Three high intensity bands are found at 408, 523–548 and 667 nm due to the ⁴G_11/2 → ⁴I_15/2, ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively, along with the other bands. Input excitation power dependence has been studied for different transitions, and the saturation effect and decrease in the slope of different transitions at higher input pump power has been explained. Heat treatments of the samples show change in crystallite phase/size and relative upconversion luminescence intensities of blue, green and red bands. The color of the phosphor emission has shown to be tunable with change in the crystal structure as well as on excitation laser power and Er³⁺–Yb³⁺ concentration. The property of color tunability of the phosphor material has been used to record the fingerprint in different colors. Also, the future prospect of the nanocrystalline phosphor material as a sensor for temperature, using FIR method, has been explored.     

Study of DNA Light Switch Ru(II) Complexes : Synthesis,Characterization, Photocleavage and Antimicrobial Activity

The three Ru(II) complexes of [Ru(phen)₂dppca]²⁺ (1) [Ru(bpy)₂dppca]²⁺ (2) and [Ru(dmb)₂dppca]²⁺ (3) (where phen = 1,10 phenanthroline, bpy = 2,2-bipyridine, dmb = 2 ,2-dimethyl 2′,2′-bipyridine and polypyridyl ligand containing a single carboxylate functionality dppca ligand (dipyridophenazine-11-carboxylic acid) have been synthesized and characterized. These complexes have been shown to act as promising calf thymus DNA intercalators and a new class of DNA light switches, as evidenced by UV-visible and luminescence titrations with Co²⁺ and EDTA, steady-state emission quenching by [Fe(CN)₆]⁴⁻ and KI, DNA competitive binding with ethidium bromide, viscosity measurements, and DNA melting experiments. The results suggest that 1, 2, and 3 complexes bind to CT-DNA through intercalation and follows the order 1 > 2 > 3. Under irradiation at 365 nm, the three complexes have also been found to promote the photocleavage of plasmid pBR322 DNA.     

Formation of pseudoisocyanine J-aggregates during thin-film formation

Thin-film formation of J-aggregated pseudoisocyanine iodide with long alkyl substituents C₁₈H₃₇ (PIC 2-18) and C₁₀H₂₁ (PIC 2-10) and ethyl substituents (PIC 2-2) with added anion was studied by spectrophotometry directly during spin-coating of its solutions. It is found that a bathochromic shift of the monomer dye absorption band maximum and extensive growth of a J-peak that is not compensated by the monomer decrease take place as the dye film forms. The refractive index and absorption coefficient of a solid dye thin film in monomeric (n _max = 2.1) and J-aggregated (n _max = 3.05) forms were measured as functions of the dispersion by spectral ellipsometry. The influence of a change in the local field factor on the spectral properties of the pseudoisocyanine dye solution in the course of both spin-coating and solid J-aggregated thin-film formation is considered. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 76–83, January–February, 2009.     

Styryl Dyes as Two-Photon Excited Fluorescent Probes for DNA Detection and Two-Photon Laser Scanning Fluorescence Microscopy of Living Cells

Spectral-fluorescent properties of benzothiazole styryl monomer (Bos-3) and homodimer (DBos-21) dyes in presence of DNA were studied. The dyes enhance their fluorescence intensity in 2–3 orders of magnitude upon interaction with DNA. Studied styrylcyanines in DNA presence demonstrate rather high values of two-photon absorption (TPA) cross-section, which are comparable with the values of TPA cross section of the rhodamine dyes. An applicability of the styrylcyanines as probes for the fluorescence microscopy of living cells was studied. It was shown that both dyes are cell-permeable but homodimer dye DBos-21 produces noticeably brighter staining of HeLa cells comparing with monomer dye Bos-3. Molecules of DBos-21 initially bind to the nucleic acids- containing cell organelles (presumable mitochondria) and are able to penetrate into the cell nucleus. Thus, homodimer styryl DBos-21 dye is viewed as efficient stain for single-photon and two-photon excitation fluorescence imaging of living cells.     

Spectroscopic Study of the Interaction of Styrylcyanine Dyes Sbo,Sil and Their Derivatives with Bovine Serum Albumin

The spectral-luminescent characteristics of newly synthesized styrylcyanine dyes on the base of dyes Sbo ((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]oxazol-3-ium iodide) and Sil ((E)-2-(4-(dimethylamino)styryl)-1,3,3-trimethyl-3H-indolium perchlorate) in aqueous solutions without and in the presence of bovine serum albumin (BSA) were studied. It was established that the absorption spectra of dyes Tol-6, Dbo-10 and Dil-10 with increasing amount of BSA appear new bands with λ_max = 505 nm, λ_max = 512 nm and λ_max = 566 nm, respectively, whose intensity increases in proportion to the amount of albumin. The intensity of the glow of the main band of fluorescence in the presence of BSA sharply increases. The binding constant (K) and the number of binding sites (N) of studied dyes with BSA were determined. The dependence of binding constants with BSA on the dipole moment of dye molecules was determined, which indicates that besides electrostatic forces of attraction between molecules styrylcyanine dyes with BSA, hydrophobic interactions are essential.     

Hydroxy and Methoxy Substituted Thiacarbocyanines for Fluorescent Detection of Amyloid Formations

In present paper series of trimethine cyanines modified in 5,5′- or 6,6′- position with hydroxy- or methoxy- substituents is studied for their ability to interact selectively with fibrillar formations. Processes of dye aggregation that accompany this interaction were also investigated. Meso-methyl trimethynecyanines with 5,5′- methoxy (7519) and hydroxy (7515) substituents strongly (up to 40 times) increase fluorescence intensity in the presence of fibrillar insulin, and also give noticeable fluorescent response on the presence of various aggregated proteins (lysozyme, β-lactoglobulin, α-synuclein A53T). 7519 and 7515 dyes can be used for fluorometric detection of fibrillar insulin at concentrations of approximately 1.5–120 microg/ml. For meso-ethyl substituted dye 7514 the ability to form H- and J-aggregates upon interaction with insulin fibrils was suggested. The model of the H- and J-aggregate packing in the protein fibrillar structure has been proposed.     

Quenching of fluorescence of porphyrin molecules in their association in binary solutions

It has been established that the absorption and fluorescence spectra of octaethylporphin (OEP), mesotetraphenylporphin (TPhP), and its complex with zinc (Zn-TPhP) in glycerol doped with dimethylformamide (DMF) or ethanol differ from the analogous spectra of these compounds in ethanol or DMF, which is due to the formation of associates of porphyrin molecules in solutions of OEP, TPhP, and An-TPhP with glycerol. For TPhP and Zn-TPhP, these differences are small, the maxima of the bands are shifted toward longer wavelengths by 3–5 nm, and their halfwidths are increased by ∼ 16%; for OEP these changes are more significant. It is shown that the duration of fluorescence of associates is much shorter than that of monomers. The probable mechanisms of quenching of the fluorescence of dimers (oligomers) of molecules were considered. It has been suggested that one of the reasons for the increased rates of deactivation of the excited states of dimers (oligomers) may be the decreased energy interval between the excited and ground states of associates as compared with that of monomers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 21–25, January–February, 2000.     

Determination of Ofloxacin using a Highly Selective Photo Probe Based on the Enhancement of the Luminescence Intensity of Eu3+—Ofloxacin Complex in Pharmaceutical and Serum Samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of ofloxacin was developed. At pH 5.1 the ofloxacin enhances the luminescence intensity of the Eu³⁺ ion in Eu³⁺- ofloxacin complex at λ_ex = 365 nm. The produced luminescence intensity of Eu³⁺-ofloxacin complex was in proportional to the concentration of ofloxacin. The working range for the determination of ofloxacin was 5.0 × 10^-9–5.0 × 10^-6 mol L^-1 with lower detection limit (LOD) and quantitative detection limit (QDL) of 3 × 10^-9 and 9 × 10^-9 mol L^-1, respectively. The enhancement mechanism of the luminescence intensity in the Eu³⁺-ofloxacin system has been also explained. The method revealed good selectivity for ofloxacin in the presence of coexisting substances and used successfully for the assay of ofloxacin in pharmaceutical preparations and serum. A comparison with other standard methods was also discussed.     

Localized excitation effects in (E,E)-2,5-<Emphasis Type="Italic">bis</Emphasis>[2-(4-N,N-dipropylaminophenyl) ethylenyl]-3,6-dimethylpyrazine and generation of its different forms in solution

Dipole moments of (E,E)-2,5-bis[2-(4-N,N-dipropylaminophenyl)ethylenyl]-3,6-dimethylpyrazine (VS365) quadrupolar dye in 1,4-dioxane and cyclohexane in addition to its instantaneous fluorescence spectra and fluorescence lifetimes in dichloromethane (pure and with added trifluoroacetic acid) were measured. Quantumchemical calculations show that the π − π conjugated system is localized in the flattest part of the molecule due to disorder in the ground-state geometry of the dye molecule and that this part is the one responsible for light absorption. The effect of localized excitation of the dye causes a considerable change in its dipole moment Δ^aμ. Various fluorescent forms of the dye that feature considerably spaced emission spectra and different fluorescence lifetimes originate by adding trifluoroacetic acid to the solution of oligophenylenevinylene in dichloromethane.     

Davydov Splitting in Spectra of Cyanine Dye J-Aggregates, Formed on the Polynucleotides

It was found in our previous work (T. Y. Ogul'chansky et al. (2001) Spectrochimica Acta Part A 57, 2705–2715) that the carbocyanine dye Cyan iPr forms J-aggregates in the groove of poly(dA)-poly(dT). In the present paper we study in detail the spectral properties and energy levels structure of the Cyan iPr J-aggregates by means of absorption and fluorescence spectroscopy and polarization measurements. The energy structure of an aggregate consists of at least two exciton zones, and dipole moments of the absorption transitions to these zones are oriented at an angle of about 90° one to another. It was supposed that the transition moment of the lower zone is parallel to the polynucleotide axis and the moment of the upper zone is perpendicular. The fluorescent transitions are possible only from the lower exciton zone, while the excitations of higher zone undergo nonradiative transitions to the lower one.     

The Correlation Between <Emphasis Type="Italic">f–f</Emphasis> Absorption and Sensitized Visible Light Emission of Luminescent Pr(III) Complexes: Role of Solvents and Ancillary Ligands on Sensitivity

The electronic absorption, excitation and sensitized visible light emission studies of three praseodymium (III) complexes: [Pr(fod)₃(bpy)], [Pr(fod)₃(phen)] and [Pr(fod)₃(bpm)]_n (fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione; bpy = 2,2'-bipyridyl, phen = 1,10-phenanthroline, bpm = 2,2'-bipyrimidine) in a series of non–aqueous solvents is presented. The f–f absorption transitions of Pr(III) are environment sensitive which is reflected by the change in the intensity (oscillator strength) and band shape (stark splitting) upon change in the solvent and/or the ligands. The sensitization of intense Pr(III) emission, in the visible region, of the complexes in solution upon excitation into the ligand centered π→π* absorption band is remarkable. The planar phen has pronounced impact and increases considerably the emission intensity of Pr(III) luminescence than the flexible bpy while bpm has been found least effective in promoting the emission intensity. The intensity of the f-f absorption and sensitized emission are correlated with the nature of the solvents. The donor solvent pyridine enhances the emission intensity of the [Pr(fod)₃(phen)] drastically and of [Pr(fod)₃(bpy)] marginally while the luminescent intensity of [Pr(fod)₃(bpm)]_n is decreased. The combined photophysical studies demonstrate that entry of the solvent molecule(s) to inner coordination sphere (complex–solvent interaction) is governed by the structure and basicity of the ancillary heterocyclic ligand attached to the Pr(III) complex. The strong donor DMSO transforms the three complexes into a similar species, [Ln(fod)₃(DMSO)₂], which results in similar electronic absorption and emission properties of the complexes in this solvent. The results demonstrate that highly luminescent praseodymium chelates can be designed with ligands containing suitable energy levels and their emission properties can be further modulated through suitable ancillary ligands and donor solvents, thus opening perspectives for applications in electroluminescent devices and luminescent probes.     

Fluorescence Interaction and Determination of Calf Thymus DNA with Two Ethidium Derivatives

In this paper, we reported the syntheses and investigation of the modes of binding to DNA of the two new ethidium derivatives containing benzoyl and phenylacetyl groups of both amines at 3-and 8- positions. The interactions between calf thymus DNA (ct-DNA) and the two derivatives, 3,8-dibenzoylamino-5-ethyl-6-phenylphenantridinium cloride (E2) and 3,8-diphenylacetylamino-5-ethyl-6-phenylphenantridinium chloride (E3), were investigated by fluorescence quenching spectra and UV-vis absorption spectra. The Stern-Volmer quenching constants, binding constants, binding sites and the corresponding thermodynamic parameters ΔH, ΔS and ΔG were calculated at different temperatures. The results indicated the formation of E2 and E3-DNA complexes and van der Waals interactions as the predominant intermolecular forces in stabilizing for each complex. In addition, increasing nucleophilicity of the functional groups at 3- and 8- positions exhibited the respectable increment the DNA binding affinities of derivatives. The results of absorption, ionic strength and iodide ion quenching suggested that the interaction mode of E2 and E3 with ct-DNA was intercalative binding. The limit of detection (LOD) of ct-DNA were 7.49 × 10⁻⁸ (n = 4) and 4.18 × 10⁻⁸ mol/l (n = 7) in presence of E2 and E3, respectively.     

Spectrofluorimetric Assessment of Doxycycline Hydrochloride in Pharmaceutical Tablets and Serum Sample Based on the Enhancement of the Luminescence Intensity of the Optical Sensor Sm<Superscript>3+</Superscript> Ion

A simple and sensitive spectrofluorimetric method for determination of trace amount of doxycycline hydrochloride (DC) in pharmaceutical tablets and serum samples was developed. In ammonia buffer solution of pH 8.9 the doxycycline hydrochloride can remarkably enhance the luminescence intensity of the Sm³⁺ ion in Sm³⁺- DC complex at λ_ex = 400 nm. The produced luminescence intensity of Sm³⁺- DC complex in DMSO is in proportion to the concentration of DC and used as optical sensor for its determination. The dynamic range for the determination of DC is 1 × 10⁻⁸ – 5 × 10⁻⁶ mol L⁻¹ and in case of quantum yield calculations is 7 × 10⁻⁹ – 5 × 10⁻⁶ mol L⁻¹ with detection limit of 6.5 × 10⁻¹⁰ mol L⁻¹. The enhancement mechanism of the luminescence intensity in the Sm³⁺- DC system has been also discussed. A comparison with other spectrofluorimetric methods for tetracycline derivatives in which Eu³⁺ ion is used instead of Sm³⁺ ion is also studied.     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.