title: Insights into the Photophysics and Supramolecular Organization of Congo Red in Solution and the Solid State.
abstract: 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.
authors.affiliation: Coimbra Chemistry Centre, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535, Coimbra, Portugal.
authors.forename: Ana L
authors.identifier: http://orcid.org/0000-0002-5083-0489
authors.initials: AL
authors.lastname: Costa
authors.affiliation: Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal.
authors.forename: Ana C
authors.identifier: http://orcid.org/0000-0001-9598-1275
authors.initials: AC
authors.lastname: Gomes
authors.affiliation: Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal.
authors.forename: Martyn
authors.identifier: http://orcid.org/0000-0002-6243-7692
authors.initials: M
authors.lastname: Pillinger
authors.affiliation: Department of Chemistry, CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal.
authors.forename: Isabel S
authors.identifier: http://orcid.org/0000-0002-2836-7715
authors.initials: IS
authors.lastname: Gonçalves
authors.affiliation: Coimbra Chemistry Centre, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535, Coimbra, Portugal.
authors.forename: João
authors.identifier: http://orcid.org/0000-0003-1848-1167
authors.initials: J
authors.lastname: Pina
authors.affiliation: Coimbra Chemistry Centre, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535, Coimbra, Portugal.
authors.forename: J Sérgio
authors.identifier: http://orcid.org/0000-0001-9708-5079
authors.initials: JS
authors.lastname: Seixas de Melo
keywords: aggregation; congo red; intercalations; layered double hydroxides; photophysics