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Systems Chemistry Approach towards Semiconductive Supramolecular Copolymers with Homo- and Heterometallophilic Interactions

Periodic Reporting for period 4 - SUPRACOP (Systems Chemistry Approach towards Semiconductive Supramolecular Copolymers with Homo- and Heterometallophilic Interactions)

Reporting period: 2021-11-01 to 2022-04-30

Understanding the molecular features governing the self-assembly of functional molecules into functional materials represents a major challenge in materials science. For example, to understand why a particular functional material (biological, optoelectronic) works efficiently, it is of utmost importance to control the molecular packing and morphology. Thus, one of the great challenges of this proposal is to program rationally designed metal complexes to create new materials with new photophysical and electronic properties. In particular, the problem to be addressed is to create functional self-assembled materials that are soluble, processable, stimuli-responsive and programmable by understanding the molecular and supramolecular features responsible for these properties. In particular, the use of Pt(II) and Pd(II) complexes and pi-conjugated ligands as building blocks has allowed us to create new materials with exciting properties.

This understanding is important for the society to create new functional materials that can be applicable in optoelectronics and life sciences. For example, the molecular organization in devices such as solar cells, transistors, etc is key to their performance. Or in another example, programming molecules to form water soluble biomaterials is pivotal to better undertstand the operation of biological systems.

The overall objectives of this project are to program metal complexes to self-assemble in a defined fashion to create new materials with superior optical and electronic properties (semiconductivity, phosphorescence, dichroism, etc). Also, these materials are expected to be formed and disassembled reversibly and controlled by external stimuli such as light and pH. This has resulted in the discovery of novel adaptive supramolecular systems. The exploitation of coordination isomerism in supramolecular self-assembly has also represented an important method to control the aggregate morphology in self-assembly. Currently, some projects based on these findings are underway. In addition, we are currently creating advanced adaptive supramolecular systems and investigating memory effects in supramolecular polymers. Finally, the implementation of some of our self-assembled Pt/Pd(II) complexes in optoelectronic devices is currently underway.
The main results achieved so far are the following:

1) in WP1, we have reported new Pt(II) and Pd(II) complexes and studied the self-assembly of this class of compounds for the first time. The detailed studies have allowed us to determine structure/property relationships for this class of compounds. We have achieved unprecedented luminiscence associated with the presence of metal-metal interactions in supramolecular polymers for some of these compounds. Moreover, moderate charge transport has been achieved for some of the systems exhibiting short metal-metal contacts.

2) In WP2, we have developed short pepdides as well as Pd(II) and Pt(II)-based self-assembled peptides and studied their aqueous self-assembly. Interestingly, the target molecules are not only stimuli-responsive depending on the pH value, but also temperature- and concentration-dependent. For some of the peptides, multiple self-assembled and secondary structures have been achieved for a single building block. Moreover, the antibacterial properties and biocompatibility of these systems have been tested.

3) In WP3, we have achieved a wide range of stimuli-responsive supramolecular polymers and assemblies, particularly by introducing light-responsive units, such as azobenzene, and/or pH-responsive units (pyridine/bipyridine) in our maolecular design. We have analyzed the mechanisms of stimuli-responsiveness by a combination of experimental and theoretical results. Moreover, the concept of coordination isomerism has been exploited for the first time to control the morphology of supramolecular polymers.
Ultimately, we have achieved controlled responsive and adaptive behaviour: Currently, and based on these results, we are attempting to create complex supramolecular systems with intelligent behaviour, trying to achieve key elements of intelligent matter such as memory, network and controlled adaptation.

4) a number of projects are still unpublished and among them we have two milestones in our group, but some of these results are confidential.
Some of our findings have gone beyond the state of the art. This includes:

1) WP1: the synthesis of the tetrapyridyl Pd(II) complexes with extended ligands is unprecedented. Given the novelty of these materials, this has gone beyond the state of the art. Exciting properties such as ultralong luminescence and semiconductivity has been achieved.

2) WP1: the discovery of new, unconventional non-covalent interactions and the existence of concomitant polymorphs is supramolecular polymers is a breackthrough in the field. This also allows establish a relationship between self-assembly and crystal engineering, which is relevant for scientists of different disciplines.

3) WP3: we exploited coordination isomerism for the first time to control self-assembly processes, which has allowed to broaden the scope of coordination isomerism and introduce a new method for pathway control in self-assembly. Recently, the concept of coordination isomerism has been further improved and developed to create acid/base-responsive supramolecular systems.

4) Although the project has already expired, we are still completing several projects. In particular, we have unravelled crowding effects in supramolecular self-assembly and we are currently using some of the supramolecular polymers and copolymers for optoelectronic applications.