Supramolecular Self-assembly Of Photoactive Cages

The development of luminescent materials has revolutionized human society, increased global productivity and improved the quality of life in dramatic fashion. Phosphorescent materials hold great promise in artificial lighting,[1]  in photocatalysis to drive chemical transformations of compounds of industrial relevance,[2]  and in sensing for the detection of a variety of analytes from nitroaromatic explosives to biological targets.[3]

Chemists have often found inspiration from the spontaneous and precise self-assembly exhibited by a giant and well-defined biological structures. In natural photosynthesis, for example, solar energy conversion is promoted through self-organized assemblies of functional chromophores. Similarly, secondary and tertiary structures of self-assembled proteins provide well-defined local environments to mediate biochemical reactions.[4]  Much effort has been devoted in recent years to the preparation of large artificial nanostructures to mimic the precise assembly of multiple protein subunits into functional superstructures.

In an effort to develop novel photoactive nanomaterials, our group has recently focused on the self-assembly between metal ions and complementary luminescent scaffolds, aiming to create high concentrations of chromophoric units that, when assembled in well-defined geometrical arrangements, exhibit emergent photophysical properties.

In this context, we have recently reported the first examples of homochiral red- and yellow-emitting supramolecular cages of the form of [Ir8Pd4]16+ based on the self-assembly between two families of enantiopure iridium(III) chromophores with Pd2+ ions (Figure 1).[5]  Although it is well known that mononuclear iridium(III) complexes exhibit remarkable photophysical properties such as high photoluminescence quantum yields and good emission color tunability across the visible spectrum, this was one of the first examples that showed that the beneficial emission properties of Ir(III) chromophores can be transferred in self-assembled 3D-cage structures.

View of the structure of cage [Ir8Pd4]16+ with space-fill representation. Credit: Diego Rota Martir & Eli Zysman-Colman
Importantly, [Ir8Pd4]16+ showed a large internal pocket volume of approximately 3480 Å3, which is of sufficient size to include large guest molecules, including mononuclear phosphorescent iridium complexes (Figures 1 and 2). As several studies[6]  have demonstrated that the photophysical properties of luminescent transition metal complexes strongly depend on the local environment, we targeted the encapsulation of a blue-emitting Ir(III) complex, TBA[Ir(dFppy)2(CN)2], within the confined cavity of our red-emitting [Ir8Pd4]16+ cage to study the nature of the energy transfer process between the Ir(III) guest and host cage. We were pleased to observe that the optoelectronic communication between the assembled host-guest components was indeed very efficient, with ultrafast energy transfer from the blue emitting TBA[Ir(dFppy)2(CN)2] complex to the red-emitting cage upon photoirradiation. As a result of the host-guest interactions, warm white light with CIE coordinates of (0.36, 0.30) was emitted by the assembly.

In light of these results, we believe that our chiral photoactive cages [Ir8Pd4]16+ are promising candidates as chiral photoactive containers capable of absorbing photons and transferring light energy to or from encapsulated guest acceptors. These assemblies open up the possibility of promoting stereoselective photocatalytic transformations, examples of which at present are exceedingly rare. On the materials front, by encapsulating luminescent guests exhibiting complementary emission colors compared to the luminescent hosts, white-light emitting materials can be efficiently produced. This can be of great importance for designing novel solution-processed electroluminescent devices.

References

  1. C. Bizzarri, E. Spuling, D. M. Knoll, D. Volz, S. Bräse, Coord. Chem. Rev., ASAP, DOI: 10.1016/j.ccr.2017.09.011.
  2. C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem. Rev. 2013, 113, 5322.
  3. D.-L. Ma, V. P.-Y. Ma, D. S.-H. Chan, K.-H. Leung, H.-Z. He, C.-H. Leung, Coord. Chem. Rev. 2012, 256, 3087.
  4. L. Yang, A. Liu, S. Cao, R. M. Putri, P. Jonkheijm, J. J. L. M. Cornelissen, Chem. Eur. J. 2016, 22, 15570.
  5. D. Rota Martir, D. Escudero, D. Jacquemin, D. B. Cordes, A. M. Z. Slawin, H. A. Fruchtl, S. L. Warriner, E. Zysman-Colman, Chem. Eur. J. 2017, 23, 14358.
  6. S. Horiuchi, H. Tanaka, E. Sakuda, Y. Arikawa, K. Umakoshi, Chem. Eur. J. 2016, 22, 17533.

This study, Homochiral Emissive Λ8- and Δ8-[Ir8Pd4]16+ Supramolecular Cages was recently published by Diego Rota Martir and Eli Zysman-Colmanin, among others in the journal Chemistry – A European Journal.

About The Author

Diego Rota Martir

Diego Rota Martir is a Doctor of Philosophy at the University of St Andrews · Organic Semiconductor Centre (OSC).

 

Eli Zysman-Colman

Eli Zysman-Colman is a Reader in Optoelectronic Materials at the University of St Andrews · EaStCHEM - Edinburgh and St Andrews Research School of Chemistry.

Speak Your Mind!

READ THIS NEXT

Understanding Missing Proteins: Why Should You Care?

We all know that proteins are important. Proteins are large macromolecules which play important roles in our bodies, working as enzymes, maintaining the structural integrity of our cells, helping cells divide, providing signals for tissues and organ systems to function harmoniously, etc. Understanding the functionalities of proteins is, thus, akin to understanding how the human […]

Genome-Wide Association Studies For Coronary Artery Disease Risk

Human disease can be loosely categorized into two broad categories, monogenic and polygenic diseases. The word monogenic means mutating a single gene is sufficient to cause a disease. Cystic fibrosis and Huntington’s disease are some examples that fall into this category. On the other hand, polygenic means that several genes (sometimes hundreds of genes) can […]

Extracting Work From Diluted Solar Radiation

In the early stages of thermodynamics, researchers focused on the study of heat and work transfer. Thermal radiation, which is to be considered in various disciplines such as engineering, atmospheric science, and astrophysics, has been treated for a long time using concepts from heat theory. Only in the last decades have scientists gradually understood that […]

B. infantis EVC001 Reduces The Genes In Bacteria That Cause Antibiotic Resistance By 90 Percent

The World Health Organization (WHO) calls antibiotic resistance “one of the biggest threats to global health, food security, and development today,” and the Centers for Disease Control and Prevention (CDC) calls it “one of the biggest public health challenges of our time.” It’s estimated that it costs the US healthcare system alone an estimated $5 […]

Fuel For Regional Economies: What Are The Benefits Of Renewable Energies?

Climate change and its effects on our ecosystems and our economies is one of the main current and future challenges. As most greenhouse gases are emitted by the energy generation sector (IPCC, 2014), there is a special need to develop renewable energies which emit fewer greenhouse gases over their lifetime than fossil energy fuels. Developing […]

4 Properties Of Metalloids

Metalloids are elements found between the metals and nonmetals on the periodic table of the elements. They are also called semimetals. Metalloids have properties which are between the properties of nonmetals and metals. Most metalloids have: 1) An appearance similar to metals. 2) But they are less conductive than metal 3) More brittle than metals […]

Quitting Smoking Means Gaining Weight, But Why?

If you quit smoking, you often gain weight. Researchers have now investigated in twins how big the difference is and whether this is also due to genes. They come to an unequivocal conclusion. Weight gain is one of the great fears of smokers who want to stop smoking. In fact, most ex-smokers gain three to […]