Triplet quantum yields in light-scattering powder samples measured by laser-induced optoacoustic spectroscopy (LIOAS)

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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.

Section: Resultsmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

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

Litman

Rodríguez

Braslavsky

et al. 2018

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“…Triplet quantum yield determinations were performed for RB and erythrosine B (EB) adsorbed on microcrystalline cellulose . These dyes are well‐known Type‐II photosensitizers, with Φ T values nearby one in common solvents.…”

Section: Resultsmentioning

confidence: 99%

“…Recently, a cell suited for this kind of systems and a sample preparation method that allows reproducible measurements was developed for the evaluation of fluorescence quantum yields in light‐scattering solids . A similar methodology was applied for the determination of triplet quantum yields .…”

Section: Determination Of Quantum Yields By Lioasmentioning

confidence: 99%

Effect of Concentration on the Photophysics of Dyes in Light‐Scattering Materials.

Rodríguez

Román

2013

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Photoactive materials based on dye molecules incorporated into thin films or bulk solids are useful for applications as photosensitization, photocatalysis, solar cell sensitization and fluorescent labeling, among others. In most cases, high concentrations of dyes are desirable to maximize light absorption. Under these circumstances, the proximity of dye molecules leads to the formation of aggregates and statistical traps, which dissipate the excitation energy and lower the population of excited states. The search for enhancement of light collection, avoiding energy wasting requires accounting the photophysical parameters quantitatively, including the determination of quantum yields, complicated by the presence of light scattering when particulate materials are considered. In this work we summarize recent advances on the photophysics of dyes in light-scattering materials, with particular focus on the effect of dye concentration. We show how experimental reflectance, fluorescence and laser-induced optoacoustic spectroscopy data can be used together with theoretical models for the quantitative evaluation of inner filter effects, fluorescence and triplet formation quantum yields and energy transfer efficiencies.

“…He also collaborated with Andr e Braun and Esther Oliveros, Karlsruhe, Jos e Luis Bourdelande, Barcelona and Silvia Braslavsky (one of the undersigning). During his last visit in M€ ulheim for some weeks in 2004, he designed a special cuvette for laser-induced optoacoustic measurements in compressed samples under controllable pressure, which was produced in the workshops of the Max Planck Institute in M€ ulheim and afterward used very successfully in Enrique's lab in Buenos Aires (6).…”

mentioning

confidence: 99%

Enrique San Román (1945–2019)

Aramendı́a¹,

Braslavsky

Lagorio

2020

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An homage to the Argentinian Photochemist Enrique San Román is presented. Enrique led the Photochemistry and Chemical Kinetics research group in the Department of Inorganic, Analytical and Physical Chemistry in the Faculty of Exact and Natural Sciences of the University of Buenos Aires from 1984 until his death in July 2019. He left a strong legacy in Chemical Kinetics and Photochemistry in Argentina. He is remembered as a meticulous and very knowledgeable scientist and teacher, a loyal friend and a generous and integer human being.