Supramolecular chemistry (celebrated by the award of the 2016 Nobel Prize in Chemistry to Feringa, Sauvage and Stoddart) led by coordination reveals to be, for two decades now, one of the most powerful contemporary synthetic approaches. Using this technique, chemists can both efficiently and quickly develop very complex molecules and control their arrangement in solid and solution states. This allows in particular cumulating in a coherent manner within intricate molecular scaffolds multiple and/or complementary physico-chemical properties. Consequently, the derivatives obtained can have very high potential in the development of new and efficient applications in fields as diverse as medicine, detection and extraction of species (toxic derivatives in particular), optoelectronics, etc ...
At the same time, a very strong attention is currently being paid to the development of Cu(I) ion complexes which in some cases can be very efficiently luminescent in the solid state. In particular, such compounds are presented as very attractive candidates to replace the emissive substances generally used in modern and energy efficient lighting devices such as OLEDs (Organic Light Emitting Devices). Indeed, these devices are very generally based on rare, strategic, expensive and sometimes very toxic precursors (such as rare earth ions or precious metals (platinum, iridium, ...)) and/or on long and expensive synthesic processes. In contrast, copper is a rather abundant element in the Earth's crust (it is the 26th most abundant element) and is found to be distributed more evenly across the planet. It has also been used for a very long time by humanity (the oldest copper objects to have been found in Mesopotamia are dated around 5000 years B. C.) and is already associated with controlled and large scale recycling processes. One of the challenges that currently remains to be overcome consists in developing very general and rapid synthetic routes of new families of stable and highly luminescent derivatives based on the Cu(I)ion. In this context, coordination driven supramolecular chemistry offers very interesting perspectives due to the wide structural variety of the molecular architectures obtained. To date, however, the general and systematic use of derivatives of the Cu(I) ion as pre-assembled precursors to elaborate new luminescent and multifunctional supramolecular assemblies remains very marginal. This is mostly due to the fact that the Cu(I) ion is presumed to present a very labile and non-directional coordination sphere, which is a priori strongly unfavorable to allow conducting highly directed, selective and rational syntheses of complex supramolecular structures.
Within the framework of the international ANR project 'P-optoelect Molmat' associating researchers from the Rennes Institute of Chemical Sciences(ISCR) and the University of Hong Kong, the first study reporting the use of a luminescent precursor Cu(I) ion in the strategy of coordination-led supramolecular synthesis has been developed and deepened. These studies first showed that a very efficient tetrametallic Cu(I) blue luminophore [1] can be produced quickly and quantitatively in a single step synthesis. This compound turns out to be a very efficient pre-organized Cu(I) supramolecular precursor allowing selective and almost quantitative syntheses of new yellow or green solid state luminescent polymetallic supramolecular assemblies. [2] The work carried out reveals that the key to achieve such results lies in the unprecedented ability of the precursor used to adapt its molecular conformation with great amplitude. In addition, the experimental and theoretical study of the photophysical properties of the new compounds obtained demonstrates the crucial importance of the flexibility of the supramolecular organization generated to promote the enhancement of the luminescence properties.
In this present study, [3] it is first demonstrated that the synthetic approach guided by the coordination chemistry highlighted can be generalized to the formation of a new green hexanuclear luminophore of the Cu(I) ion bearing remarkable luminescence properties, whose solid-state behaviour is rationalized thanks to a theoretical study. Above all, by modifying the structure of the pre-organized bimetallic precursor of the Cu(I) ion, it is observed that concerted dissociation / reassociation phenomena of the elementary building blocks introduced in these syntheses take place. This leads selectively and in a single step to the preparation of supramolecular derivatives bearing completely new structural complexity. These results thus reveal a new facet of the potential offered by the introduction of the Cu(I) ion in supramolecular assembly processes guided by coordination. It is directly linked to the increased structural flexibility of pre-assembled Cu(I) precursors, giving access to even more complex and efficient spontaneous self-organizing processes. In addition, the new supramolecular structures obtained exhibit again remarkable luminescence properties exalted in the solid state.
This study augurs broad perspectives of evolution for this original synthetic approach allowing the development of new luminescent multifunctional supramolecular assemblies of the Cu(I) ion having original geometries and multifunctional properties.
Learn more on this work
- [1] M. ElSayed Moussa, S. Evariste, H.-L. Wong, L. Le Bras, C. Roiland, L. Le Polles, B. Le Guennic, K. Costuas, V. W.-W. Yam, C. Lescop,
Solid State Highly Emissive Cu(I) Metallacycle: Promotion of Cuprophilic Interactions at the Excited States.
Chem. Commun. 2016, 52, 11370-11373.
- [2] S. Evariste, A.M. Khalil, M. Elsayed Moussa, A. K.-W. Chan, E. Y.-H. Hong, H.-L. Wong, B. Le Guennic, G.Calvez, K. Costuas, V. W.-W. Yam, C. Lescop,
Adaptive coordination-driven supramolecular syntheses toward new polymetallic Cu(I) luminescent assemblies,
J. Am. Chem. Soc., 2018, 140, 12521–12526. Front cover picture.
- [3] M.Elsayed Moussa, A.M. Khalil, S. Evariste, H.-L. Wong, V. Delmas, B. Le Guennic, G.Calvez, K. Costuas, V. W.-W. Yam, C. Lescop,
Intramolecular rearrangements guided by adaptive coordination-driven reactions toward highly luminescent polynuclear Cu(I) assemblies,
Inorg. Chem. Front., 2020, doi:10.1039/C9QI01595G. Front cover picture.
