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 (approximate to 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 approximate to 170ps 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.
keywords
LAYERED DOUBLE HYDROXIDES; AGGREGATION-INDUCED EMISSION; AMYLOID-BETA-PEPTIDE; SOLVATION DYNAMICS; ENERGY-TRANSFER; DYE MOLECULES; AZO-DYE; COMPLEX; BINDING; FILMS
subject category
Chemistry; Physics
authors
Costa, AL; Gomes, AC; Pillinger, M; Goncalves, IS; Pina, J; de Melo, JSS
our authors
Ana Catarina Costa Gomes Alves
Assistant Researcher
Ana Luísa Costa
Researcher
Isabel Maria de Sousa Gonçalves
Associate Professor
Martyn Pillinger
Principal Researcheracknowledgements
We acknowledge funding by FEDER (Fundo Europeu de Desenvolvimento Regional) through COMPETE (Programa Operacional Factores de Competitividade). National funding through the FCT (Fundacao para a Ciencia e a Tecnologia) within the projects Coimbra Chemistry Centre (PEst-OE/QUI/UI0313/2014) and FCOMP-01-0124-FEDER-029779 (FCT ref. PTDC/QEQ-SUP/1906/2012) is thanked. This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. The FCT is acknowledged for a PhD grant to A.L.C. (ref. SFRH/BD/88806/2012) and post-doctoral grants to A.C.G. (ref. SFRH/BPD/108541/2015) and J.P. (ref. SFRH/BPD/108469/2015).