Eosin Y Triplet State as a Probe of Spatial Heterogeneity in Microcrystalline Cellulose

Rodríguez, Hernán B.; Román, Enrique San; Duarte, Paulo; Machado, I. Ferreira; Ferreira, L.F. Vieira

doi:10.1111/j.1751-1097.2012.01152.x

Cited by 15 publications

(20 citation statements)

References 44 publications

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“…The average of DRLFP and LIL signals normalized to unity at t = 0 can be fitted for EoY by a triexponential function: Signal = 0.08 exp(Àt/0.30 ms) + 0.43 exp(Àt/1.62 ms) + 0.49 exp (Àt/3.80 ms). A more detailed study on the triplet decay was performed earlier (18), reporting a bimodal lifetime distribution with maxima peaking at ca. 0.75 and 3.00 ms.…”

Section: Resultsmentioning

confidence: 97%

“…Previous studies were carried out by us on the photophysics of two xanthene dyes, Eosin Y (EoY) and Phloxine B (PhB) included into microcrystalline cellulose particles (structures in Scheme 1). The concentration dependence of their absorption and fluorescence spectra was studied, their aggregation tendency was analyzed and the decay of singlet and triplet states was investigated.…”

Section: Introductionmentioning

confidence: 99%

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Photophysics of Xanthene Dyes at High Concentrations in Solid Environments: Charge Transfer Assisted Triplet Formation

Litman

Rodríguez

Braslavsky

et al. 2018

Photochem & Photobiology

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The photophysical behavior of two xanthene dyes, Eosin Y and Phloxine B, included in microcrystalline cellulose particles is studied in a wide concentration range, with emphasis on the effect of dye concentration on fluorescence and triplet quantum yields. Absolute fluorescence quantum yields in the solid-state were determined by means of diffuse reflectance and steady-state fluorescence measurements, whereas absolute triplet quantum yields were obtained by laser-induced optoacoustic spectroscopy and their dependence on dye concentration was confirmed by diffuse reflectance laser flash photolysis and time-resolved phosphorescence measurements. When both quantum yields are corrected for reabsorption and reemission of radiation, Φ values decrease strongly on increasing dye concentration, while a less pronounced decay is observed for Φ . Fluorescence concentration quenching is attributed to the formation of dye aggregates or virtual traps resulting from molecular crowding. Dimeric traps are however able to generate triplet states. A mechanism based on the intermediacy of charge-transfer states is proposed and discussed. Calculation of parameters for photoinduced electron transfer between dye molecules within the traps evidences the feasibility of the proposed mechanism. Results demonstrate that photoactive energy traps, capable of yielding dye triplet states, can be formed even in highly-concentrated systems with random dye distributions.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Photophysics of Xanthene Dyes at High Concentrations in Solid Environments: Charge Transfer Assisted Triplet Formation

Litman

Rodríguez

Braslavsky

et al. 2018

Photochem & Photobiology

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“…As an example, Figure 4 shows the fluorescence decay of a This bimodal distribution consisted of lifetime populations centred at 0.76 and 2.97 ms, which were assigned, respectively, 25 to Eosin Y present in the amorphous and crystalline regions of the cellulose. 8 Therefore, it seems reasonable to conclude that the shorter lifetime found herein for 2-Me-4-OMe TG adsorbed on microcrystalline cellulose,  1 = 2.58 ± 0.50 ns, corresponds to the emission of dye molecules present in the amorphous regions, 30 where the relatively lax structure of the polysaccharide matrix would allow for larger non-radiative deactivation rates. In contrast, the longer lifetime,  2 = 4.49 ± 0.34 ns, can be assigned to dye molecules adsorbed on the crystalline regions, in which the compact structure of the matrix would lower the chance of non- 45 radiative deactivation.…”

Section: Resultsmentioning

confidence: 61%

“…6 In consequence, quenching of the adsorbed dyes by oxygen is negligible and, for this reason, room-temperature phosphorescence and room-temperature delayed fluorescence can 40 be readily observed. 7,8 Microcrystalline cellulose consists of a relatively disordered and flabby amorphous region and of a relatively ordered and compact crystalline region. The accessibility of these two regions to the dye molecules depends upon the extent of swelling of the cellulose matrix, which is 45 caused by the interactions with the solvent from which the dyes are being adsorbed.…”

Section: Introductionmentioning

confidence: 99%

Fluorescence enhancement of a fluorescein derivative upon adsorption on cellulose

Lopez

Crovetto

Álvarez‐Pez

et al. 2014

Photochem Photobiol Sci

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9-[1-(2-Methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (2-Me-4-OMe TG) is a fluorescein derivative dye whose photophysical properties show a remarkable pH dependence. In aqueous solution the fluorescence quantum yield (Φf) of its anionic species is nearly a hundred times higher than that of its neutral species. Such a large difference in Φf makes 2-Me-4-OMe TG useful as an "on-off" pH indicator. Here we report that adsorption on the surface of microcrystalline cellulose exerts a profound effect upon the photophysical properties of 2-Me-4-OMe TG. On the solid only the dye neutral species is observed and its Φf is 0.31 ± 0.10, which is approximately thirty times higher than the value found for the neutral species in aqueous solution (Φf = 0.01). 2-Me-4-OMe TG and Dabcyl (DB) were co-adsorbed on the surface of microcrystalline cellulose to study the transfer of excitation energy from the former to the latter. In the absence of the dye, the formation of DB aggregates is observed at concentrations greater than 0.34 μmol per gram of cellulose, while in the presence of 2-Me-4-OMe TG the formation of DB aggregates is thoroughly inhibited. The quenching of fluorescence of 2-Me-4-OMe TG by DB reaches efficiencies as high as 90% for the most concentrated samples.

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“…The measurements of triplet states lifetime give information about the properties of the microenvironment[ 43 ] around Rose Bengal probe. As mentioned in the methodology section, using Eq 2 , we fitted the data from the phosphorescence decay of singlet oxygen from reversed micelles and we obtained the excited triplet lifetime of Rose Bengal and simultaneously the lifetime of singlet oxygen.…”

Section: Resultsmentioning

confidence: 99%

Structuration in the Interface of Direct and Reversed Micelles of Sucrose Esters, Studied by Fluorescent Techniques

et al. 2015

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BackgroundReactors found in nature can be described as micro-heterogeneous systems, where media involved in each micro-environment can behave in a markedly different way compared with the properties of the bulk solution. The presence of water molecules in micro-organized assemblies is of paramount importance for many chemical processes, ranging from biology to environmental science. Self-organized molecular assembled systems are frequently used to study dynamics of water molecules because are the simplest models mimicking biological membranes. The hydrogen bonds between sucrose and water molecules are described to be stronger (or more extensive) than the ones between water molecules themselves. In this work, we studied the capability of sucrose moiety, attached to alkyl chains of different length, as a surface blocking agent at the water-interface and we compared its properties with those of polyethylenglycol, a well-known agent used for this purposes. Published studies in this topic mainly refer to the micellization process and the stability of mixed surfactant systems using glycosides. We are interested in the effect induced by the presence of sucrose monoesters at the interface (direct and reverse micelles) and at the palisade (mixtures with Triton X-100). We believe that the different functional group (ester), the position of alkyl chain (6-O) and the huge capability of sucrose to interact with water will dramatically change the water structuration at the interface and at the palisade, generating new possibilities for technological applications of these systems.ResultsOur time resolved and steady state fluorescence experiments in pure SEs micelles show that sucrose moieties are able to interact with a high number of water molecules promoting water structuration and increased viscosity. These results also indicate that the barrier formed by sucrose moieties on the surface of pure micelles is more effective than the polyoxyethylene palisade of Triton X-100. The fluorescence quenching experiments of SEs at the palisade of Triton X-100 micelles indicate a blocking effect dependent on the number of methylene units present in the hydrophobic tail of the surfactant. A remarkable blocking effect is observed when there is a match in size between the hydrophobic regions forming the apolar core (lauryl SE/ Triton X-100). This blocking effect disappears when a mismatch in size between hydrophobic tails, exists due to the disturbing effect on the micelle core.

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Eosin Y Triplet State as a Probe of Spatial Heterogeneity in Microcrystalline Cellulose

Cited by 15 publications

References 44 publications

Photophysics of Xanthene Dyes at High Concentrations in Solid Environments: Charge Transfer Assisted Triplet Formation

Photophysics of Xanthene Dyes at High Concentrations in Solid Environments: Charge Transfer Assisted Triplet Formation

Fluorescence enhancement of a fluorescein derivative upon adsorption on cellulose

Structuration in the Interface of Direct and Reversed Micelles of Sucrose Esters, Studied by Fluorescent Techniques

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