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Final Report Summary - AU_HYDROGEL (New luminescent hydrogels and chemosensors derived from alkynyl gold(I) complexes)

Aurophilic interactions are common in gold(I) compounds and are responsible for the formation of dimers, oligomers and supramolecular polymers. Moreover, gold(I) compounds usually exhibit interesting luminescent properties that can be modulated by the presence of Au···Au interactions [1].

The main objectives of this project were to synthesise new gold(I) compounds able to: i) form luminescent gels or, alternatively, other complexes architectures in water; ii) act as chemosensors for relevant biological and/or environmental species.

These goals have been successfully met by means of the design of several families of gold(I) compounds, where the variation on the functional groups was responsible of their distinctive properties (see Figure 1 in the attached Supplementary Material).

The thermodynamic properties of previously reported gold(I) hydrogelators were studied and it was shown that the aggregation behavior strongly depends on small changes on the water-soluble phosphine attached to the gold(I) atom [2]. Moreover, it was observed that the photophysical properties of these compounds in different solvents greatly depend on their ability to aggregate which is at the same time related to the polarity of the solvents and concentration (Figure 2) [3].

It was demonstrated that small changes on the chemical structure of the compounds have a great impact on the self-assembled architectures originated in water and several organic solvents, as well as in their luminescent properties (Figure 3) [4].

The introduction of coumarins as chromophoric units resulted in an efficient phosphorescence emission at room temperature due to the enhanced intersystem crossing originated by the presence of the Au(I) atoms. Broad emission bands were observed in most cases due to the formation of organized aggregates in solution (Figure 4, above), in agreement with microscopic characterisation (Figure 4, below) [5]. Preliminary experiments showed that some dinuclear compounds are good candidates for the detection of metal cations.

Other variation in the chemical structure consisted on the introduction of chromophoric units with chelating properties (bipyridine, terpyridine). These compounds are able to interact with metal cations and this behaviour can be used to control aggregation and therefore the optical properties of the systems (Figure 5) [6].

Trinuclear gold(I) compounds containing tripropargylamine and several water soluble phosphines were prepared are their aggregation resulted on the formation of long fibers. These compounds present a versatile sensing character and are able to interact both with metal cations and organic species (Figure 6) [7].

A last variation consisted on the design of gold(I)-silver(I) bimetallic structures in water. These systems were demonstrated to self-assemble and form organised structures in this solvent. Moreover, they exhibit high luminescence in the solid state, which can be finely tuned by the chemical nature of the counterion (Figure 7) [8].

A part of this research have been already published in several peer-reviewed international journals and additional manuscripts are currently under preparation. The results have been also presented in important international conferences such as the International Symposium on Macrocyclic and Supramolecular Chemistry and the IUPAC International Symposium on Photochemisty. The research results related to this project can be relevant for several high-tech applications such as the design of drug-delivery systems, nanoreactors and luminescent chemosensors and therefore they can have a positive impact on the technology industry in Europe.

[1]. J. C. Lima, L. Rodríguez, “Applications of gold(I) alkynyl systems: a growing field to explore”, Chem. Soc. Rev. 2011, 40, 5442-5456.
[2]. R. Gavara, E. Aguiló, C. Fonseca-Guerra, L. Rodríguez, J. C. Lima, “Thermodynamic aspects of aurophilic hydrogelators”, Inorganic Chemistry 2015, 54, 5195-5203.
[3]. R. Gavara, J. C. Lima, L. Rodríguez, “Effect of solvent polarity on the spectroscopic properties of an alkynyl gold(I) gelator. The particular case of water”, Photochemical & Photobiological Sciences 2016, 15, 635-643.
[4]. E. Aguiló, R. Gavara, C. Baucells, M. Guitart, J. C. Lima, J. Llorca, L. Rodríguez, “Tuning supramolecular aurophilic structures: the effect of counterion, positive charge and solvent”, Dalton Transactions 2016, 45, 7328-7339.
[5]. R. Gavara, E. Aguiló, J. Schur, J. Llorca, I. Ott, L. Rodríguez, “Study of the effect of the chromophore and nuclearity on the aggregation and potential biological activity of gold(I) alkynyl complexes”, Inorganica Chimica Acta 2016, 446, 189-197.
[6]. Manuscript in preparation.
[7]. Manuscript in preparation.
[8]. Manuscript in preparation.

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