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Insights into the Photophysics and Supramolecular Organization of Congo Red in Solution and the Solid State
Author(s) -
Costa Ana L.,
Gomes Ana C.,
Pillinger Martyn,
Gonçalves Isabel S.,
Pina João,
Seixas de Melo J. Sérgio
Publication year - 2017
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201601236
Subject(s) - aqueous solution , quantum yield , photoisomerization , chemistry , absorption (acoustics) , photochemistry , congo red , fluorescence , ultrafast laser spectroscopy , absorption spectroscopy , monolayer , supramolecular chemistry , molecule , spectroscopy , materials science , isomerization , adsorption , organic chemistry , catalysis , biochemistry , physics , quantum mechanics , composite material
Steady‐state and time‐resolved absorption and fluorescence measurements are reported for Congo Red (CR) in aqueous and dimethylsulfoxide (DMSO) solutions. The very low fluorescence quantum yield (≈10 −4 ) for CR in dilute solutions together with the absence of a triplet state indicates that internal conversion is the dominant deactivation route with more than 99.99 % of the quanta loss (attributed to the energy gap law for radiationless transitions). Although no direct evidence for trans – cis photoisomerization was obtained from absorption or fluorescence data, the global analysis of fs‐transient absorption data indicates the presence of a photoproduct with a lifetime of ≈170 ps that is suggested to be associated with such a process. Spectral data for more concentrated CR solutions indicate the presence of oblique or twisted J‐type aggregates. These results are compared with spectra for CR in the solid state (sodium salt) and intercalated in a layered double hydroxide via a one‐step co‐precipitation route. Powder XRD and electronic spectral data for the nanohybrid indicate that the CR guest molecules are intercalated as a monolayer consisting of slipped cofacial J‐type aggregates.