The mutual influence of two different dyes on their sensitized fluorescence (cofluorescence) in nanoparticles from complexes

We have studied the fluorescence sensitization and quenching for pairs of different dyes simultaneously incorporated into nanoparticles from complexes M(diketone)₃phen, where M(III) is La(III), Lu(III), or Sc(III); diketone is p-phenylbenzoyltrifluoroacetone (PhBTA) or naphthoyltrifluoroacetone (NTA); and phen is 1,10-phenanthroline. We have shown that, upon formation of nanoparticles in the solution in the presence of two dyes the concentrations of which are either comparable with or lower than the concentration of nanoparticles (<20 nM), the intensities of the sensitized fluorescence of dyes in nanoparticles in binary solutions and in solutions of either of the dyes coincide. We have found that the intensity of sensitized fluorescence of small (<20 nM) concentrations of rhodamine 6G (R6G) or Nile blue (NB) increases by an order of magnitude upon simultaneous introduction into nanoparticles of 1 μM of coumarin 30 (C30), while the intensity of fluorescence of C30 sensitized by complexes decreases by an order of magnitude. The same effect is observed as 1 μM of R6G are introduced into nanoparticles with NB ([NB] ≤ 20 nM). The increase in the fluorescence of dye molecules upon their incorporation from the solution into nanoparticles from complexes is noticeably lower than that expected from the proposed ratio of concentrations of complexes and dyes in nanoparticles. Analysis of the obtained data indicates that the introduction of large concentrations of C30 or R6G dyes into nanoparticles makes it possible to prevent large energy losses due to impurities or upon transition to a triplet state that arises during the migration of the excitation energy over S ₁ levels of complexes. Energy accumulated by these dyes is efficiently transferred to another dye that is present in the solution at lower concentrations and that has a lower-lying S ₁ level, which makes it possible to increase its fluorescence by an order of magnitude upon its incorporation into nanoparticles.     

Luminescence of Nile red as indicator of composition of nanoparticles from diketonate complexes of trivalent metals

We study the sensitization of fluorescence of Nile red in nanoparticles formed in aqueous solutions of complexes of Al, In, Sc, and Lu with DBM, DBM, and phen and of complexes of In with MBTA and phen. We show that, at concentrations of Nile red of 2–50 nM and complexes of 10–30 μM, the fluorescence intensity of Nile red in aqueous solutions increases by 1.5–2 orders of magnitude compared to its fluorescence in H₂O. We find that, at these concentrations of Nile red in solutions of complexes Al, the dye is completely contained in nanoparticles from these complexes. We show that Nile red molecules are inhomogeneously distributed in nanoparticles from complexes and, upon the completion of the formation of nanoparticles, dye molecules tend to be localized in regions of nanoparticles formed from diketonate complexes M(diketone)₃phen (M is Lu or In) and Al(DBM)₃. Upon the localization of Nile red in these regions, the maximum of its fluorescence spectrum shifts toward ∼600 nm and, upon the penetration of Nile red into nanoparticles from Sc complexes, the shift of the maximum of its fluorescence spectrum compared to the spectrum in water does not exceed 10 nm. The shifts of the spectra are collated with the ability of ions to form diketonate and hydroxy diketonate complexes. We demonstrate that the fluorescence of Nile red is efficiently sensitized, not only upon its penetration into nanoparticles formed from complexes, but also upon its adsorption on the nanoparticle surface when Nile red molecules are introduced in solutions of already formed nanoparticles.     

Particular features of incorporation of coumarin 30 into nanoparticles from metal complexes and the intensity of its columinescence

We have studied the sensitized fluorescence of coumarin 30 incorporated into nanoparticles from complexes of p-phenylbenzoyltrifluoroacetone and 1,10-phenanthroline with Y, La, Lu, Gd, Al, and Sc ions in 10% alcoholic-aqueous solutions. We have shown that, upon formation of nanoparticles from complexes of Y(III) and Ln(III) ions, coumarin 30 molecules are completely incorporated from the solution into nanoparticles from complexes up to dye concentrations in the solution comparable with the concentration complexes. For the nanoparticles under study, in the whole range of the examined dye concentrations, concentration quenching of the coumarin 30 cofluorescence has not been observed. Our results show that coumarin 30 is incorporated into lanthanide and yttrium complexes as a synergistic bidentate ligand. The possibility of creating brightly luminescent markers that absorb not only in the range of 360?C370 nm, but also in the range of 440?C450 nm, and have a narrow fluorescence spectrum with ??_max = 520 nm has been demonstrated.     

Influence of complexing ion on the fluorescence sensitization efficiency for oxazine dyes in nanoparticles of Sc,Eu, Sm,and Lu diketonates

The fluorescence sensitization regularities have been investigated for oxazine dyes (Nile blue, cresyl violet (oxazine-9), and oxazine-170) in nanoparticles of complexes of 2-naphthoyltrifluoroacetone with trivalent ions of rare-earth metals. The fluorescence sensitization efficiencies of dyes in nanoparticles from the Sc(III), Eu(III), Sm(III), and Lu(III) complexes are compared. It is shown that the fluorescence sensitization efficiencies of dyes in nanoparticles from the Sc(III), Eu(III), and Sm(III) complexes has similar values and greatly exceed that for nanoparticles from the Lu(III) complexes. The quantum yields of sensitized fluorescence are determined for dyes in nanoparticles from the Sc(III), Eu(III), and Sm(III) complexes. The nanoparticles doped with oxazine-170 from Eu(III) complexes are found to have the strongest fluorescence.     

Enhancement of the fluorescence of triphenylmethane dyes caused by their interaction with nanoparticles from β-diketonate complexes

We have studied the absorption and fluorescence spectra of Malachite Green and Crystal Violet in aqueous and alcoholic-aqueous solutions in which nanoparticles from Ln(III) and Sc(III) diketonates are formed at concentrations of complexes in a solution of 5–30 μM. We have shown that, if the concentrations of the dyes in the solution are lower than 0.5 μM, dye molecules are incorporated completely into nanoparticles or are precipitated onto their surface. The fluorescence intensity of these incorporated and adsorbed Malachite Green and Crystal Violet molecules increases by several orders of magnitude compared to the solution, which takes place because of a sharp increase in the fluorescence quantum yields of these dyes and at the expense of the sensitization of their fluorescence upon energy transfer from β-diketonate complexes entering into the composition of nanoparticles. We have shown that, if there is no concentration quenching, the values of the fluorescence quantum yield of the Crystal Violet dye incorporated into nanoparticles and adsorbed on their surface vary from 0.06 to 0.13, i.e., are close to the fluorescence quantum yield of this dye in solid solutions of sucrose acetate at room temperature. The independence of the fluorescence quantum yield of Crystal Violet on the morphology of nanoparticles testifies to a high binding constant of complexes and the dye. The considerable fluorescence quantum yields of triphenylmethane dyes in nanoparticles and sensitization of their fluorescence by nanoparticle-forming complexes make it possible to determine the concentration of these dyes in aqueous solutions by the luminescent method in the range of up to 1 nM.     

Columinescence of dye molecules in nanostructures of metal ion complexes

The mechanism of columinescence (fluorescence sensitization) of dyes incorporated in nanostructures of metal complexes is studied. It is shown for the first time that the columinescence of dyes is due to the transfer of excitation energy from ligands and metal ions of complexes that form nanostructures. It is proven that the dye columinescence of rhodamine 6G (R6G) molecules incorporated into nanostructures of Al(DBM)₃phen, Al(DBM) _n (OH)_{6 ? 2n} , and Eu(DBM)₃phen (DBM is dibenzoylmethane) nanostructures is completely determined by the singlet excitation energy migration from ligands to R6G molecules. It is shown that, at small concentrations of R6G, the R6G columinescence intensity is lower in nanostructures of metal complexes with a high probability of S-T conversion and that this difference disappears at large concentrations of R6G. In the case of Nile blue (whose S ₁ level lies below the ⁵ D ₀ level of Eu(III)) incorporated in nanostructures of Eu(DBM)₃phen complexes, as well as in nanostructures of Al(DBM)₃phen and Gd(DBM)₃phen complexes with admixture of Eu complexes, we observed the S-S energy transfer from DBM to NB in addition to the delayed sensitized fluorescence of NB previously observed in nanostructures of Eu complexes, which was caused by the energy transfer from the ⁵ D ₀ level of Eu(III) to NB. At dye concentrations below 100 nM, the efficiency of NB sensitization due to the migration of singlet excitation energy from DBM is lower than in the case of the energy transfer from Eu(III) ions, while, at large concentrations of the dye, the S-S energy transfer successfully competes with the sensitization of NB by Eu(III) ions. The use of dye columinescence makes it possible to easily determine dye concentrations of 2–100 nM in solutions with standard spectrofluorimeters.     

Particular features of manifestation of energy migration toward impurity in nanoparticles of metal complexes

We measure the fluorescence quantum yields (q _fl) of complexes of Al, Sc, Y, In, Lu, and Gd with dibenzoylmethane in aqueous and isopropanol solutions at different concentration ratios of ions and dike-tone. We reveal that, for the examined solutions, qfl of complexes varies more than by two orders of magnitude under the influence of the heavy atom. It is found that a considerable decrease in q _fl and τ_fl of ligands of complexes of listed ions caused by the influence of heavy atoms weakly affects the intensity of sensitized fluorescence of Nile red and rhodamine 6G molecules introduced into nanoparticles from these complexes in aqueous solutions. The revealed result is explained by the comparability of the singlet exciton free path length and the dimension of nanoparticles under study. We show that a lower fluorescence intensity of heavy metal complexes makes it possible to decrease its contribution in the range of the cofluorescence maximum of rhodamine 6G and to monitor the occurrence of the dye in the aqueous solution down to the concentration of 0.05 nM. We show that, in nanoparticles from Eu complexes, further fluorescence quenching of dibenzoylmethane is observed, as well as the appearance of cofluorescence of rhodamine 6G, the intensity of which is comparable with its intensity in nanoparticles of other complexes. The appearance of this cofluorescence cannot be explained by the existence of S-S energy migration.     

Energy transfer from Eu(III) and Tb(III) complexes to dyes in their mixed nanostructures. I

The formation of nanostructures that consist of complexes of β-diketones with 1,10-phenanthroline and involve dyes of the polymethine, triphenylmethane, oxazine, and xanthene series is observed in aqueous solutions. It is found that nanostructures of complexes of Ln(III) ions and dyes are reliably observed at concentrations of Ln complexes from 0.5 to 5 μM and at dye concentrations above 5 nM. Nanostructures of complexes Eu(MBTA)₃phen, Eu(NTA)₃phen, Eu(PTA)₃phen, Tb(PTA)₃phen, Gd(MBTA)₃phen, and Lu(MBTA)₃phen with dyes are studied, where MBTA is n-methoxybenzoyltrifluoroacetone, NTA is naphthoyltrifluoroacetone, PTA is pivaloyltrifluoroacetone, and phen is 1,10-phenanthroline. It is shown that nanostructures formed can contain dye molecules not only inside a nanostructure of Ln complexes but also on its outer shell. It is proved that, at a dye concentration in the solution of the order of nanomole or higher, the formation of mixed nanostructures of Eu complexes and dyes whose S ₁ level is below the ⁵ D ₀ level of Eu(III) leads to the quenching of the luminescence of Eu(III) and gives rise to the sensitized luminescence of dyes. The energy transfer efficiency from Eu(III) ions to dye molecules is determined by the ability of these molecules to incorporate into nanostructures of Eu complexes. The effect of the formation of nanostructures on the shape and position of the spectra of luminescence and absorption of dyes is studied. Comparison of the sensitized luminescence intensities of Nile blue in structures of Eu, Lu, and Gd complexes shows that the greater part of the excitation energy of Eu complexes is transferred directly from ions to dye molecules according to the inductive-resonance energy transfer mechanism rather than by means of energy migration over singlet levels of organic ligands in complexes of a nanostructure.     

Energy transfer from Eu(III) complexes to dyes in their mixed nanostructures. II

The effects of the concentration of a number of dyes in an aqueous solution and of the method of formation of mixed nanostructures of dyes and Eu(MBTA)₃phen (MBTA is p-methoxybenzoyltrifluoroacetone; phen is 1,10-phenanthroline) complexes that form these structures on the luminescence decay kinetics of Eu(III) ions are studied. It is shown that, in the concentration range 5–50 nM of Nile blue, the concentration dependences of the luminescence decay and of the decrease in τ _lum of Eu(III) nearly coincide and are nearly linear. The dependence of the ratio of I _lum of Eu(III) to the intensity of the sensitized delayed fluorescence of Nile blue on the delay time of the probe pulse is analyzed; it is found that the majority of dye molecules incorporated in nanostructures of Eu(MBTA)₃phen complexes emit sensitized delayed fluorescence with times 1–50 μs. Analysis of the effect of the structure of nanostructures on the quenching of I _lum of Eu(III) by the dye at different concentrations of Eu(III) shows that nanostructures of Eu(MBTA)₃phen and Eu(NTA)₃phen (NTA is 2-naphthoyltrifluoroacetone) complexes appear in the aqueous solution at a concentration of Eu(III) of 0.1 μM (the MBTA or NTA concentration is 50 μM, and the concentration of phen is 17 μM) and exist in the solution at the Eu(III) concentrations up to ～5 μM. This confirms the conclusion on the occurrence range of nanostructures of Ln complexes previously made based on the analysis of columinescence in these structures.     

Spectral and luminescent properties of coumarins in nanoparticles from metal ion complexes

We have studied the absorption spectra of complexes of trivalent ions Y, La, Lu, and Sc with p-phenylbenzoyltrifluoroacetone that were introduced into a solution of 90% H₂O + 10% iso-C₃H₇OH in the absence and presence of either 1,10-phenanthroline or coumarins 6, 7, or 30. We have shown that these coumarins, as well as phenanthroline, are synergistic bidentate ligands that are incorporated into complexes up to concentrations comparable with concentrations of complexes and that stabilize them in the solution. We have studied the dependences of the fluorescence (cofluorescence) intensity (I _cofl) of the coumarins on their concentration in nanoparticles from the complexes mentioned above. We have shown that, in nanoparticles from complexes of Y(III), Ln(III), and Sc(III), I _cofl of coumarin 30 at high concentrations is higher than I _cofl of coumarins 6 and 7. In addition, up to concentrations of coumarin 30 comparable with the concentration of complexes in nanoparticles, there is no concentration quenching of its fluorescence. For coumarins 6 and 7, which are prone to association in the solution under study, the process of incorporating coumarins into complexes competes with their association, which leads to concentration quenching and changes in the shape of their cofluorescence spectra.     

Energy migration toward a dye in nanoparticles from complexes with short fluorescent state lifetimes

We have studied regular features of the fluorescence sensitization (cofluorescence) of coumarin 30 and rhodamine 6G introduced into nanoparticles from complexes Ln(PhBTA)₃phen, where PhBTA is p-phenylbenzoyltrifluoroacetone and Ln is a triply charged Pr, Nd, Sm, Eu, Er, or Yb ion, which absorbs in the fluorescence range of ligands of complexes and dyes. We show that both the cofluorescence intensities (I _cofl) of rhodamine 6G in nanoparticles from Sm and Eu complexes and the behavior of intensity I _cofl on the content of rhodamine 6G coincide with the corresponding data obtained for nanoparticles from La and Lu complexes doped with rhodamine 6G molecules. A considerable decrease in I _cofl of rhodamine 6G is observed only in nanoparticles from complexes Nd(PhBTA)₃phen. In nanoparticles from Pr, Nd, Sm, Eu, Er, and Yb complexes doped with coumarin 30, it has been observed that, depending on the choice of the central ion, I _cofl of coumarin 30 is 2 to 80 times lower compared to I _cofl of the dye in nanoparticles from La and Lu complexes. A separate analysis of the influence of these ions on the energy transfer from complexes to coumarin 30 and on the fluorescence intensity of coumarin 30 incorporated into nanoparticles from these ions showed that a decrease in I _cofl of coumarin 30 by a factor of 2?C20 occurs due to the reduction of ??_fl of ligands of complexes under the influence of the interaction with Pr, Nd, Sm, Eu, Er, and Yb ions. Since ??_fl of complexes La(PhBTA)3phen is ??2 ps, while that of complexes Gd(PhBTA)3phen is ??1 ps, then, in nanoparticles with a maximal decrease in I _cofl of coumarin 30, ??_fl of complexes is reduced to ??0.1 ps. It has been found that, in nanoparticles from complexes with this ??_fl, energy migration over complexes takes place. However, as distinct from nanoparticles from La, Lu, and Y complexes, the free path length of singlet excitons in nanoparticles from complexes of absorbing ions is smaller than the nanoparticle size.     

Energy transfer from the singlet levels of diketones and dyes to lanthanide ions in nanoparticles consisting of their diketonate complexes

The energy transfer from the S ₁ levels of p-phenylbenzoyltrifluoroacetone (PhBTA) and dyes to different Ln³⁺ ions is studied in nanoparticles (NPs) composed of complexes of this diketone with Ln³⁺ and 1,10-phenanthroline (phen) and doped with dye molecules. The quenching rate constants in the NPs consisting from complexes of Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Ho³⁺, Er³⁺, and Tm³⁺ are determined from the data on the quenching of sensitized (cofluorescence) and ordinary fluorescence of coumarin 30 (C30) and rhodamine 6G (R6G). The quenching rate constants vary from ≤5 × 10¹¹ to 10¹³ s^?1 for the fluorescence quenching of PhBTA by different Ln³⁺ ions, while the quenching of dye fluorescence occurs at rates of the order of 10⁹ s^?1. In the case of complexes with the Pr³⁺ ions, the fluorescence quenching of PhBTA in NPs composed of its complexes is accompanied by sensitized luminescence of Pr³⁺. The quenching observed is due to a nonradiative energy transfer from the S ₁ states of ligands and dyes to these ions. It is shown that in NPs composed of complexes with Eu³⁺, Yb³⁺, and Sm³⁺ the cofluorescence of C30 is quenched via the electron-transfer mechanism. The study of quenching of cofluorescence and fluorescence of dyes in NPs composed of mixed complexes of La³⁺ and Nd³⁺ (Ho³⁺) shows that the observed quenching of fluorescence and cofluorescence is governed mainly by the quenching of the S ₁ state of dyes when the Nd³⁺ (Ho³⁺) content does not exceed 5–10% and by the quenching of the S ₁ state of a ligand when the Nd³⁺ (Ho³⁺) content exceeds 50%. It is assumed that the high rate constant of energy transfer from the S ₁ level of ligands to ions Pr³⁺, Nd³⁺, Ho³⁺, Er³⁺, and Tm³⁺ in NPs composed of beta-diketonate complexes is caused by exchange interactions.     

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.     

Luminescent spectral properties of rhodamine derivatives while binding to serum albumin

We have studied the effect of blood serum albumin on the absorption and fluorescence spectra of rhodamine C (RC), rhodamine 6G (R6G), and rhodamine 3B (R3B). Interaction of the dye with protein is assessed using the binding parameters: binding constants and concentrations of binding sites. We have studied the effect of temperature on the binding parameters. We have observed that heating a mixture of the dye solution with protein for 30 min leads to an increase in the binding constant for rhodamine 3B with protein by a factor of 2, while the concentration of binding sites increases by a factor of 2.3. This is explained by features of the globular protein structure and a change in its conformation when heated. We have shown that rhodamine 3B at a concentration of 10⁻⁵ M is the most effective among the studied rhodamine dyes for application as a fluorescent probe when studying conformational changes in blood serum protein. Report given at the Third International Conference on Liquid State Physics: Current Problems, May 27–31, 2005, Kiev, Ukraine. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 380–384, May–June, 2006.     

等色染料离子对浮选光度法研究-四溴荧光素*罗丹明6G体系

本文研究了四溴荧光素（ＴＢＦ）、罗丹明６Ｇ（Ｒ６Ｇ）等色染料离子对浮选光度法测定锗、铂和铁的方法。首先将被测金属离子形成的［ＭｅＬｎ（Ｒ６Ｇ）ｍ］（Ｌ：配位体,ｍ、ｎ为整数）有机溶剂浮选物,用碱解析并反萃于水相。而后加入与罗丹明６Ｇ等色的四溴荧光素溶液继续浮选,将形成的等色染料离子对Ｒ６ＧＴＢＦ浮选物溶解于丙酮。于５３０ｎｍ处测定吸光度值。由于２ｍ个染料同时吸收同一波长的光,而提高了方法灵敏度。测定Ｇｅ、Ｐｔ和Ｆｅ的摩尔吸光系数均在１０５Ｌｍｏｌ－１ｃｍ－１以上     

Heavy-water-based solutions of rhodamine dyes: photophysical properties and laser operation

Photophysical properties of heavy-water-based rhodamine dye solutions have been investigated, with a view to assess the suitability of heavy water as a solvent for high-power, high-repetition-rate dye lasers and amplifiers. We have measured the quantum yield of fluorescence of the commonly used dyes rhodamine-6G, rhodamine-B and kiton-red, dissolved in heavy water, ethanol and normal water. The performance of a heavy-water-based pulsed rhodamine-6G dye laser has been investigated in broadband, as well as in narrowband wavelength-tunable resonator configurations, yielding laser efficiencies comparable to those achieved with ethanolic solutions of the same dye. We have also studied the thermo-optic properties of normal and heavy water, using the Z-scan technique. Finally, photodegradation rates for laser dyes have been compared in heavy water, normal water and ethanol. Our results establish heavy water as a solvent superior to both ethanol and normal water, on account of the lower thermo-optic effects and the higher photostability of rhodamine dyes when dissolved in heavy water. Received: 8 February 2002 / Published online: 8 August 2002     

Relative Quantum Yield Measurements of Coumarin Encapsulated in Core-Shell Silica Nanoparticles

Fluorescent silica nanoparticles encapsulating organic fluorophores provide an attractive materials platform for a wide array of applications where high fluorescent brightness is required. We describe a class of fluorescent silica nanoparticles with a core-shell architecture and narrow particle size distribution, having a diameter of less than 20 nm and covalently incorporating a blue-emitting coumarin dye. A quantitative comparison of the scattering-corrected relative quantum yield of the particles to free dye in water yields an enhancement of approximately an order of magnitude. This enhancement of quantum efficiency is consistent with previous work on rhodamine dye-based particles. It provides support for the argument that improved brightness over free dye in aqueous solution is a more general effect of covalent incorporation of fluorescent organic dyes within rigid silica nanoparticle matrices. These results indicate a synthetic route towards highly fluorescent silica nanoparticles that produces excellent probes for imaging, security, and sensing applications.     

Mechanisms of Fluorescence Quenching in Donor—Acceptor Labeled Antibody—Antigen Conjugates

The cyanine dyes Cy5 and Cy5.5 are presented as a new long wavelength-excitable donor-acceptor dye pair for homogeneous fluoroimmunoassays. The deactivation pathways responsible for the quenching of the fluorescence of the antibody-bound donor are elucidated. Upon binding of the donor dye to the antibodies at low dye/protein ratios, its fluorescence quantum yield rises to unity. Higher dye/protein ratios lead to progressive aggregation of the dyes, which results in quenching of monomer fluorescence due to resonance energy transfer (RET) from the monomers to the nonfluorescent dimers. The dependence of the quenching efficiency on the labeling ratio is described quantitatively by assuming a Poisson distribution of the dyes over the antibodies. The maximum fluorescence intensity per antibody is obtained at a labeling ratio of 4. Upon formation of the antibody-antigen complex, electron transfer and RET to the antigen-bound acceptor dye occur. Steady-state and time-resolved fluorescence measurements reveal that approximately 50% of the donor quenching is due to RET, while the residual quenching effect is caused by the static quenching process.     

Solvatochromic Studies of Fluorescent Azo Dyes: Kamlet-Taft (π*, α and β) and Catalan (Spp, SA and SB) Solvent Scales Approach

A new metal ion-responsive azo-based fluorescent probes have been synthesized and characterized by NMR spectral techniques. Steady-state fluorometric study has been used to analyze the spectroscopic and photophysical characteristics of dye derivatives in various solvents. The fluorescence properties of these dyes are strongly solvent dependent, the wavelength of maximum fluorescence emission shifts to the red. The Kamlet-Taft and Catalan’s solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The hydroxy substituted azo dye formed complexes with several metal ions (Co²⁺, Hg²⁺, Ni²⁺ and Cu²⁺) and fluorescence quenching with metal ions reveal that it can be used as a new fluorescence sensor to detect the Cu²⁺ ion.     

Laser-induced synthesis of metal–carbon materials for implementing surface-enhanced Raman scattering

Metal–carbon materials exhibiting surface-enhanced Raman scattering have been synthesized by laser irradiation of colloidal systems consisting of carbon and noble metal nanoparticles. The dependence of the Raman scattering intensity on the material composition and laser irradiation conditions has been investigated. The possibility of recording the Raman spectrum of organic dye rhodamine 6G, deposited in amount of 10^–6 M on the substrate obtained from a colloidal solution is demonstrated.