Interaction between dyes and polyelectrolytes. XII. Excitation energy transfer between bound dyes

Methylene blue-photosensitized isomerization of cis-p-(phenylazo) phenyltrimethylammonium iodide to the transisomer was used advantageously to investigate the effect of polyanions on the triplet excitation energy trasfer between cationic dyes in aqueous media. The efficiency of the excitation energy transfer was improved by the addition of potassium poly(vinyl sulfate) (PVS), potassium poly(styrene-sulfonate) (PSS), sodium poly(acrylate) (PAA), and sodium poly(methacrylate) (PMA) and was dependent on the polyanion concentration in the system. PVS and PSS were much more effective than PAA and PMA. The efficiency of the excitation energy transfer under the most appropriate conditions was about 67 times higher than in the absence of polyanions. Correlation with dye binding to polyanions and the efficiency of the excitation energy transfer between dyes was discussed.     

Interaction between dyes and polyelectrolytes. X. Excitation energy transfer in cationic dye–polyanion system

The quantum yield for the trypaflavine-photosensitized oxidation of 1-(methylthio)ethyl-3-carbamoylpyridinium chloride to 1-(methylsulfinyl)ethyl-3-carbamoylpyridinium chloride increased with increase in the concentration of methylene blue added. It was inferred that the increase in the quantum yield is due to the excitation energy transfer from trypaflavine to methylene blue. The efficiency of excitation energy transfer was enhanced on addition of potassium poly(vinyl sulfate) and was dependent on the polyanion/dye ratio. The efficiency of excitation energy transfer at the most appropriate polyanion/dye ratio was about 5 times as high than that in the absence of polyanion. The binding of dye to potassium poly(vinyl sulfate) was investigated spectrophotometrically. Correlation with the dye binding to potassium poly(vinyl sulfate) and the efficiency of excitation energy transfer between dyes was discussed.     

Study of electronic excitation energy transfer between cyanine dye molecules noncovalently bound to DNA

Electronic excitation energy transfer between molecules of carbocyanine dyes noncovalently bound to DNA was studied. 3,3′,9-Triethyl-5,5′-dimethyloxacarbocyanine iodide and 3,3′-dimethyl-9-ethyloxacarbocyanine iodide were used as energy donors, and 3,3′-diethylthiacarbocyanine iodide served as an acceptor dye. The fluorescence decay kinetics of the donors and its quenching by the acceptor in the presence of DNA were measured. The microphase model was used for interpretation of the experimental data, with allowance for concentrating dye molecules in the vicinity of DNA molecules.     

Interaction between dyes and polyelectrolytes. XI. Photoreduction of methylene blue bound to potassium polystyrenesulfonate

The effect of potassium polystyrenesulfonate (PSSK) on the quantum yield (Φ) in the photoreduction of methylene blue (MB) by allylthiourea was investigated. MB was bound to PSSK in monomeric, dimeric, or slightly aggregated form, depending on the polyanion–dye ratio (P/D). At a relatively lower P/D in which most MB molecules were bound to PSSK in dimeric or slightly aggregated form, the value of Φ was smaller than that at a P/D of zero. On the other hand, at a higher P/D, in which most MB molecules were bound to PSSK in monomeric form, the value of Φ was larger than that at a P/D of zero. It was suggested that the lower reactivity of dimeric or slightly aggregated MB on PSSK was caused by the length of its lifetime which is shorter than that of the monomeric form. It was also suggested that the increase in Φ at higher P/D was caused by the decreased deactivation of the triplet excited MB by the ground-state MB.     

Rate of excitation energy transfer between fluorescent dyes and nanoparticles

Because of the sensitivity of the rate of Coulomb interaction induced long range resonance energy transfer (RET) on the distance between the donor (D) and the acceptor (A) molecules, the technique of FRET (fluorescence resonance energy transfer) is popularly termed as “spectroscopic ruler” and is increasingly being used in many areas of biological and material science. For example, the phenomenon is used to monitor the in vivo separation between different (bio)polymers/units of (bio)polymers and hence the dynamics of various biomolecular processes. In this work, we examine the distance and the orientation dependence of RET in three different systems: (i) between a conjugated polymer and a fluorescent dye, (ii) between a nanometal particle (NMP) and a fluorescent dye and (iii) between two NMP. We show that in all the three cases, the rate of RET follows a distance dependence of d^−σ where exponent σ approaches 6 at large distance d (Förster type dependence) but has a value varying from 3–4 at short to intermediate distances.     

Effect of polyelectrolytes on aggregation of a cyanine dye

The effect of poly(acrylic acid) and poly(methacrylic acid) on the molecular state of a cationic cyanine dye (3,3′-diethyl-2,2′-thiacarbocyanine iodide) was studied. Gels based on the above polymers were shown to efficiently absorb an oppositely charged dye. The absorption of dye ions by a gel induced their aggregation. It was shown that, in the acrylic acid-based gels, H-aggregates, dimers, and single ions of the dye coexist. In gels containing methacrylic acid units, dye ions mainly formed H-aggregates. A comparison of aggregation of dye ions in the gels with that in aqueous solutions of corresponding polyelectrolytes was performed. When dye ions were immobilized in a gel network, the proportion of the ions forming the H-aggregates was considerably larger than that in solutions. The effect of the gel network charge density on the aggregation of dye ions was investigated. It was shown that an increase in the fraction of charged units in network chains facilitates aggregation.     

Interaction between dyes and polyelectrolytes. I. Effect of polyelectrolytes on the reaction of methylene blue with 1-benzyl-1,4-dihydronicotinamide

The effect of polyelectrolytes on the reaction of methylene blue with 1-benzyl-1,4-dihydronicotinamide was investigated. An accelerating effect was observed on addition of sodium polystyrenesulfonate of poly(potassium p-styrenesulfonate). On the other hand, deceleration was observed on addition of potassium polyvinylsulfate. No appreciable effect was observed when sodium p-toluenesulfonate or potassium chloride was used as an electrolyte. An obvious color change was observed when methylene blue is bound to these anionic polyelectrolytes. Some correlations with spectral change of methylene blue and acceleration or deceleration effect are discussed.     

Electronic excitation energy transfer between molecules of carbocyanine dyes in complexes with DNA

Electronic excitation energy transfer has been carried out between molecules of carbocyanine dyes bound noncovalently to DNA. 3,3′,9-Triethyl-5,5′-dimethyloxacarbocyanine iodide was used as an energy donor and 3,3′-diethylthiacarbocyanine iodide as an acceptor dye. In this process, the band belonging to the donor is observed in the fluorescence excitation spectrum of the acceptor. Donor fluorescence quenching by the acceptor in the presence of DNA was studied. The results of the experiments are discussed in terms of the Dye-DNA stoichiometric complex formation and with respect to concentrating the dyes in the microphase (pseudophase) of the biopolymer.     

Effect of polymer microenvironment on excitation energy migration and transfer

Excitation energy transfer between the dye pair acriflavine (donor) to rhodamine-6G (acceptor) in various polymers [polyvinyl alcohol (PVA), cellulose acetate, and polymethyl methacrylate (PMMA)] was studied using steady-state and time-resolved fluorescence spectroscopy at room temperature. In all these polymers, at higher acceptor concentrations, direct energy transfer from acriflavine to rhodamine-6G followed the F?rster theory, which is indicated by the agreement in the values of the observed critical transfer distance with that calculated from spectral overlap. On the other hand, at low acceptor concentrations, the excitation energy migration influences the kinetics, resulting in a significantly higher value of the observed critical transfer distance, which is explained on the basis of Loring et al. (Loring, R. F.; Anderson, H. C.; Fayer, M. D. J. Chem. Phys. 1984, 80, 5731-5744) and Huber (Huber, D. L. Phys. Rev. B: Condens. Matter Mater. Phys. 1979, 20 2307-2314) theories. It was observed that the spectral overlap for donor-donor transport (excitation migration) and donor-acceptor transfer (energy transfer) and thereby other energy transfer parameters were influenced by the microenvironment of the polymers. The efficiency of energy transfer (eta) was the highest in PMMA and the lowest in PVA. Further, the study of acceptor dynamics under energy transfer showed that the rise time of the acceptor also depends on the nature of the polymer microenvironment.     

Comments on the energy transfer dye laser

Kinetic analysis of an energy transfer dye laser is presented. The laser gain function depends on the molecular parameters and on the concentrations of both the donor and acceptor. For the low signal limit the gain shows linear dependence on either the donor or the acceptor concentrations for a fixed donor-acceptor concentration ratio. This behavior has been confirmed experimentally.     

Electronic excitation energy transfer between nucleobases of natural DNA

Transfer of the electronic excitation energy in calf thymus DNA is studied by time-resolved fluorescence spectroscopy. The fluorescence anisotropy, after an initial decay starting on the femtosecond time scale, dwindles down to ca. 0.1. The in-plane depolarized fluorescence decays are described by a stretched exponential law. Our observations are consistent with one-dimensional transfer mediated by charge-transfer excited states.     

Studies on fluorenscence resonance energy transfer between CdS nanoparticles and DOCAI dyes

The water-soluble CdS nanoparticles were synthesized in aqueous solution. A novel fluorescence resonance energy transfer (FRET) system with CdS nanoparticles as energy donors and 3,30-diethyl-oxadicarbocyanine iodide (DOCAI) dyes as energy accepter has been developed.     

Photoinduced energy transfer and charge transfer on squarylium cyanine dyes

A series of squarylium cyanine dyes (Sqs) were synthesized to explore their applications in functional devices.Preliminary investigation on the mechanism involved in these devices was carried out.Spectroscopic behavior of Sqs with porphyrin (P),8-hydroxyquinolium aluminum (Alq) and ruthenium bipyridyl complex (Ru(bipy)) in solution,in film and on nanocrystalline TiO2 was investigated,respectively.A mechanism including photoinduced energy transfer and charge transfer processes was suggested in the corresponding practical devices.By means of doping,a red organic electroluminescent device (ELD) using Sq-doped Alq as the emission layer (EML) has been developed,and the total light to electricity efficiency of nanocrystalline TiO2 electrode based on using Sq-doped Ru(bipy) as photosensitizer has been improved greatly in the whole visible region,particularly in the red area above 600 nm.     

Complexes of polyelectrolyte hydrogels with organic dyes: Effect of charge density on the complex stability and intragel dye aggregation

The swelling behavior of polyelectrolyte gels based on poly(diallyldimethylammonium chloride) (copolymers of diallyldimethylammonium chloride and acrylamide with the variable composition) and poly(methacrylic acid, sodium salt) in the presence of organic water soluble dyes (alizarin, naphthol blue black, rhodamine) was studied. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depend on the charges of the polymer network and the dye, and also on the dye concentration. Stability of the gel–dye complexes in a salt solution of NaCl and Al₂(SO₄)₃ was studied. It was shown that the complex stability in the salt solution depends on the charge density of the polymer chains forming the gel. The increase of charge density of polymer generally leads to the enhancement of the complex stability. For the systems with the fraction of charged poly(diallyldimethylammonium chloride) monomer units above 0.5 the release of alizarin to the external solution of Al₂(SO₄)₃ reservoir is practically completely suppressed. The obtained results show that oppositely charged dyes are generally from stable complexes with polyelectrolyte gels. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1209–1217, 1999     

Interaction between charge-regulated surfaces in the presence of polyelectrolytes

This work gives a brief overview of the backgrounds of the self-consistent mean-field theory as applied to the problem of interaction between charge-regulated surfaces in the presence of polyelectrolytes. A general algorithm for obtaining a self-consistent solution is described, and the asymptotic properties of the solution at close separations are analyzed. Known limitations of the self-consistent field approximation are discussed, highlighting the role of local effects and system equilibration.

     

Interaction between dyes and polyelectrolytes. VI. Metachromatic behavior of methylene blue induced by potassium poly(vinyl sulfate) and its homologs

Effect of structure of potassium poly(vinyl sulfate) and its homologs on the metachromatic behavior of methylene blue was investigated spectrophotometrically. The metachromatic behavior with addition of polyanions was followed by the changes in the molar extinction coefficient of the 664 nm band of methylene blue and in the wavelength of metachromatic band. Important factors for metachromasy were the number of anionic sites per polymer molecule, the degree of polymerization, and the flexibility of polymer chain. It was found that the amount of KCl or urea required to destroy the metachromasy was a useful measure for estimating the binding strength of methylene blue to polyanions.     

Enhancement of electronic excitation energy transfer in the colloidal crystals of colloidal silica suspensions doped with fluorescent dyes

The efficiency of electronic excitation energy transfer from photo-excited rhodamine 110 (Rh110, energy donor) to rhodamine B (RhB, energy acceptor) in an exhaustively deionized colloidal silica suspension has been studied. This colloidal suspension shows Bragg reflection due to the formation of colloidal crystals and the Bragg-peak wavelength is controllable by the volume fraction of the silica spheres. When the Bragg-peak wavelength matches with the fluorescence band of Rh110, a depletion was observed in the Rh110 fluorescence spectrum. This means the fluorescence of Rh110 is partially trapped due to the Bragg reflection inside the crystal lattice. In the coexistence of RhB, the enhancement of RhB fluorescence intensity was observed. These facts clearly indicate the trapped photon energy of Rh110 is efficiently transferred to RhB within the colloidal crystals. The quantitative measurements showed that the enhancement of the transfer efficiency is 20% (or slightly more) in the present experimental conditions.     

Transfer of electronic excitation energy between randomly mixed dye molecules in the channels of zeolite L

Host-guest materials containing strongly fluorescent donor and acceptor molecules have been prepared. Fine-tuning of the donor to acceptor distance in this material allows beautiful visible and quantitative observation of electronic excitation energy transfer phenomena. Oxonine and pyronine have been used as guest molecules and zeolite L as host. The dyes have been inserted by ion exchange. Stationary state and time-resolved experiments have been carried out with zeolite crystals of 300 and 700 nm size in the dye concentration range of 10(-4) mol/L up to 0.042 mol/L. The fluorescence decay of the donor and the pumping of the acceptor via energy transfer, which can be well observed, became faster with increasing loading. The behavior of the system follows requirements expected for F?rster energy transfer material.