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Understanding and exploiting competitive solvent interactions in supramolecular polymerization: from solutions to bulk materials

Periodic Reporting for period 1 - SolSupPol (Understanding and exploiting competitive solvent interactions in supramolecular polymerization: from solutions to bulk materials)

Reporting period: 2021-08-01 to 2023-07-31

Three decades after the first reports on one-dimensional aggregates of repeating monomers held together by non-covalent interactions, the field of supramolecular polymers is blooming. The dynamic nature of supramolecular polymers and their consequent high responsiveness to external stimuli render them attractive candidates for optoelectronic applications. To tune their properties and control their function, a fundamental understanding of such complex systems is of key importance. In this regard, the overall goal of the project is to get insights into monomer-monomer and competitive solvent interactions in supramolecular polymerization and to exploit such knowledge to tune the assembly of supramolecular polymers and tailor their photophysical properties. The ultimate aim is the preparation of targeted functional systems based on supramolecular interactions in view of potential applications as optical and energy materials.
In the first part of the project, we investigated and exploited solvent-induced chirality transfer to bias the helicity of supramolecular polymers and enable circularly polarized luminescence from ordered assemblies of achiral aggregation-induced-emission chromophores. Intriguingly, the helicity of the supramolecular assemblies was found to be dictated not only by the solvent chirality but also buy the nature of the solubilizing alkyl chains of the monomer. Moreover, the molecular architecture of the side chains was found to have a profound impact on the bulk properties of the investigated systems, leading to appreciable changes in the interchromophoric packing and thermal properties of the materials.
In the second part of the project, we exploited the self-assembly of functional monomers and the targeted tuning of the experimental conditions to implement and regulate singlet fission within supramolecular polymers. In the investigated systems, the H-bond driven assembly of a supramolecular scaffold guides the organization of the functional pendants into exohelical frameworks. Through-space interactions mediate fast singlet conversion, affording independent triplets with lifetimes exceeding those found in crystalline materials. Subtle changes in monomer design enable the modulation of excited state kinetics as a result of distinct molecular arrangements within the assemblies.
A detailed dissemination plan at different audience levels guaranteed the high impact of this research, strongly promoting further scientific advances in the research field and boosting applications.
Solvent-induced chirality transfer represents an intriguing, yet poorly exploited tool to tune the assembly of supramolecular polymers in view of potential applications as functional materials. In particular, the exploitation of chiral solvents to induce circularly polarized luminescence in aggregation-induced-emission-based supramolecular polymers is unprecedent in literature. Moreover, despite the high potential of aggregation-induced emission materials for optoelectronic applications, systematic studies on the influence of monomer design on bulk properties are scarce. The results of this project constitute a proof-of-concept, demonstrating that supramolecular materials based on solvent-induced chirality transfer are intriguing platforms with emerging structure-property relationships for chiroptical and spintronic applications.
On the other hand, the exploitation of one-dimensional supramolecular templates to enable SF within ordered nanostructures of photoactive pendants is unprecedent in literature. Leveraging directional secondary interactions between monomeric units provides a novel strategy to mitigate the strength of interchromophoric interactions, while imparting a supramolecular order reminiscent of crystalline materials. The results provides new insights in the quest for fast singlet conversion and long-lived triplets, highlighting the critical role of conformational dynamic and chiral organization in regulating excited-state dynamics within non-covalent, ordered architecture and outlining the potential of singlet fission to disclose the structure and dynamics of supramolecular polymers. The innovative implementation of singlet fission in supramolecular polymers contributes to elucidate the structure-property relationships regulating the process, addressing some of the major issues that currently limit the efficiency of singlet fission-based photovoltaics.
Overall, the work carried out within this project contributes towards addressing the global challenges of sustainability and clean energy of the United Nations and the European Green Deal. The outcomes of this high-gain research strongly contribute to advancements within the research field of supramolecular polymers, enabling the design of functional, adaptive materials based on supramolecular interactions and ultimately contributing to the knowledge-based society. On one hand, the knowledge gained from the study of solvent-induced circularly polarized emission will foster advances in a wide range of chirality-related applications. On the other hand, fundamental investigation on singlet fission is of crucial importance for applications in solar energy conversion schemes.
Overview of the project