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Influence of Negatively Charged Interfaces on the Ground and Excited State Properties of Methylene Blue ¶
Author(s) -
Severino Divinomar,
Junqueira Helena C.,
Gugliotti Marcos,
Gabrielli Dino S.,
Baptista Mauricio S.
Publication year - 2003
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2003)0770459ioncio2.0.co2
Subject(s) - chemistry , micelle , photochemistry , dimer , excited state , sodium dodecyl sulfate , flash photolysis , monomer , analytical chemistry (journal) , aqueous solution , reaction rate constant , organic chemistry , kinetics , physics , quantum mechanics , nuclear physics , polymer
Properties of the ground and excited states of methylene blue (MB) were studied in negatively charged vesicles, normal and reverse micelles and sodium chloride solutions. All these systems induce dimer formation as attested by the appearance of the dimer band in the absorption spectra ( λ D ∼ 600 nm ). In reverse micelles the dimerization constant ( K D ) corrected for the aqueous pseudophase volume fraction is two–three orders of magnitude smaller than K D of MB in water, and it does not change when W 0 is increased from 0.5 to 10. Differences in the fluorescence intensity as a function of dimer–monomer ratio as well as in the resonance light scattering spectra indicate that distinct types of dimers are induced in sodium dodecyl sulfate (SDS) micelles and aerosol‐OT (sodium dioctyl sulfoxinate, AOT) reversed micelles. The properties of the photoinduced transient species of MB in these systems were studied by time‐resolved near infrared (NIR) emission (efficiency of singlet oxygen generation), by laser flash photolysis (transient spectra, yield and decay rate of triplets) and by thermal lensing (amount of heat deposited in the medium). The competition between electron transfer (dye*–dye) and energy transfer (dye*–O 2 ) reactions was accessed as a function of the dimer–monomer ratio. The lower yield of electron transfer observed for dimers in AOT reverse micelles and intact vesicles compared with SDS micelles and frozen vesicles at similar dimer–monomer ratios is related with the different types of aggregates induced by each interface.