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pi-Electronic Gel Hybrids: Towards Smart<br/>Photoactive Nanomaterials

Final Report Summary - GELBRID (pi-Electronic Gel Hybrids: Towards Smart Photoactive Nanomaterials)

GELBRID was a Marie Curie-IIF project aiming at the preparation and extensive characterization of soft hybrid materials targeted to optoelectronic applications. Our strategy to make hybrid soft materials was based on supramolecular gels formed by the spontaneous self-assembly of suitably designed organic molecules. These gels are made of extended three-dimensional fibrillar networks whose interstitial spaces are filled with solvent molecules and can host various molecules and materials such as allotropes of carbon and inorganic nanocrystalline systems. This approach opens up new possibilities to engineer self-assembled gels and get new hybrid materials that merge the features of individual constituents, generating totally new properties and functions. To attain this goal the GELBRID team designed and synthesized some hybrid molecules made of pi-conjugated systems and hydrogen-bonding motifs based on short peptides. A breakthrough result of the project was the sonication-induced gelation of a peptide functionalized squaraine dye.

This material was extensively characterized with spectroscopic and microscopic techniques, which revealed the nucleation growth mechanism of the self-assembly. Notably, addition of a minuscule amount of single-walled carbon nanotubes was found to considerably accelerate the sonication-induced self-assembly of the gelator, by facilitating a heterogeneous nucleation process that led to a supramolecular hybrid gel. This work paves the way to the rational design of nanostructured hybrid materials made of organic dyes (squaraines) and carbon allotropes (fullerenes, CNTs, and eventually graphene), with cheap and facile methods. The application of these intimately mixed hybrid materials in optoelectronic devices is a subject worth of further studies.

In another work, with the objective of exploiting the inherent ability of peptide units to form directional hydrogen bonding with fixed distance and flexible dihedral angles, we designed and synthesized a pi-conjugated peptide system composed of an oligo(p-phenylenevinylene) and an alanine based dipeptide. Under suitable conditions, the pi-conjugated peptide self-assembled into helical gel nanostructures, exhibiting excellent luminescence properties. The hybrid gels were prepared by combining p-type pi-conjugated peptides with n-type materials such as perylenediimides and fullerenes. Flash photolysis time-resolved microwave conductivity studies showed that the hybrid gel exhibits enhanced charge carrier mobility and carrier lifetime, with respect to the gel prepared in the absence of n-type materials. This effect is due to an efficient interaction between the fibrous assembly of the pi-conjugated peptide and the mixed n-type materials, thanks to donor-acceptor interfaces that undergo photoinduced charge separation.

Finally, we started the development of an organic-inorganic hybrid system made of zinc oxide nanowires and an oligo(p-phenylenevinylene) derivative functionalized with carboxylic acid moieties. Morphological and photophysical studies are in progress to understand and exploit the merit of this approach.

As briefly summarized above, the relevant progress made in gel materials in the frame of GELBRID can stimulate further research and new applications in the fields of materials science and optoelectronic devices. The fruitful experience matured within GELBRID has made the Researcher a highly qualified researcher who has high chances to get a leading position in academia or industry. Most importantly, the incoming institution (CNR-ISOF) has now gained a deep know-how in the area of gel materials, which was totally lacking previously. The novelty of the concepts elaborated and the effectiveness of the collaborations established during the GELBRID project are a springboard to establish extended collaboration between CNR-ISOF and Indian Institutions through joint projects in the frame of the Horizon 2020 Programme.

For more information:

Nicola Armaroli, CNR Research Director
Project Coordinator