Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Final Activity Report Summary - SISMA (Supramolecular Interactions in Smart Materials)

Spectroscopic properties of isolated dipolar chromophores and small multichromophoric assemblies containing the same chromophores have been experimentally investigated. Spectroscopic differences between these two cases, resulting from supramolecular interactions, have been analysed and interpreted through a theoretical model proposed by the fellow. The importance of self-organisation driven by interchromophore interactions in the case of flexible multichromophores has been pointed out. In the case of multipolar systems, obtained by branching of dipolar units via a common core, the fundamental role of coherent interactions, non-electrostatic in nature, has been demonstrated. The effect is a strong cooperative enhancement of nonlinear optical properties such as two-photon absorption (TPA).

After this first step, new multichromophoric systems have been designed, synthesised and investigated. The design stage was guided by previous obtained results and by theoretical predictions. Thus, the second stage of the project concerned new multichromophoric systems of desired supramolecular structure presenting stronger interchromophore interactions. Structures with constrained geometry but also flexible structures possibly mimicking real situations encountered in bulk systems for applications have been obtained. As expected, even more important supramolecular effects were observed on nonlinear optical properties (namely TPA). The developed theoretical model allowed to explain these effects as strongly dependent on contributions arising from interaction terms usually neglected in the description of interacting molecules.

This first combined theoretical and experimental demonstration stresses the importance of correctly taking into account supramolecular interactions when designing and studying systems for applications, where environmental conditions play a major role and active units are in close proximity. These results clearly demonstrate the possibility of tuning the desired response by exploiting supramolecular interactions.

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