New method of harvesting artificial light using organic nanotubes

Organic nanotubes provide artificial light-harvesting for solar cells.

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Researchers developed a method for harvesting artificial light using organic nanotubes, which can be used for solar cells, photocatalysis, optical sensors, and tunable multi-color light-emitting materials.

Plants and photosynthetic microorganisms gather sunlight and send it to the reaction center via energy and electron transfer stages, eventually storing it as chemical energy.

The surrounding proteins accurately align the antenna chromophores in the light-harvesting complexes into arrays, allowing efficient energy movement between them.

In recent years, there has been a lot of interest in mimicking natural photosynthetic systems and understanding the fundamental processes of energy transmission, particularly for systems that require energy conversion and storage.

Dr. Supratim Banerjee of the Indian Institute of Science Education and Research (IISER) Kolkata and Dr. Suman Chakrabarty of the S. N. Bose National Center for Basic Sciences (SNBNCBS) Kolkata conducted experimental and computational studies on artificial light harvesting in organic nanotubes derived from the union of an organic fluorescent molecule and a therapeutically important biopolymer.

The former is an amphiphilic cationic molecule known as cyano stilbenes (an organic molecule with fluorescent properties known to exhibit enhanced emission in its aggregated state). The latter is an anionic therapeutically important bio-polymer known as heparin (used as an anti-coagulant during surgery and in post-operative treatments) in aqueous media.

This approach can help solar cells, photocatalysis, optical sensors, and tunable multi-color light-emitting materials.

The production of nanotubes with vivid greenish-yellow emission by an electrostatically driven co-assembly process was studied in this study. 

The nanotubes functioned as highly efficient energy donors (antennae) in a system that emulated the natural photosynthetic process, donating energy to acceptor dyes like Nile Red and Nile Blue, resulting in emission color tuning from greenish-yellow to orange-red, including white light.

The energy transfer phenomena demonstrated in this study is known as FRET (Förster resonance energy transfer). It is important in various applications, such as DNA/RNA structure identification, mapping biological membranes, and real-time PCR assays. 

Solar energy is being converted for storage as chemical or electrical energy in the future, and the process of energy transfer is critical in such applications.

The formation of the nanotubes was studied using absorption and fluorescence spectroscopy, transmission electron microscopy (TEM), and fluorescence lifetime imaging microscopy (FLIM) in the study published in Chemical Science, the flagship journal of the Royal Society of Chemistry. 

The simulation investigations also showed and measured the local molecular level interactions and packing of the cyano stilbene chromophores that resulted in the development of one-dimensional nanostructures.

Molecular Dynamics (MD) simulation studies revealed that the cyano stilbene molecules formed cylindrical structures in the presence of heparin. The local molecular level interactions and packing of the cyano stilbene chromophores that formed one-dimensional nanostructures were visualized and quantified.

Due to these systems’ ability to respond to temperature changes through the FRET process, they were also used as ratiometric emission thermometers in the temperature range of 20–90 °C, which sense temperature based on the variation in emission intensity at two different wavelengths. This demonstrated a useful use for these artificial light-harvesting systems.

Journal Reference:

  1. Shubhra Kanti Bhaumik,Dibyendu Maity, etal. Efficient light harvesting in self-assembled organic luminescent nanotubes. Chemical Science.DOI:10.1039/D3SC00375B
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