Researchers have developed a novel method of harnessing artificial light by utilizing organic nanotubes inspired by natural photosynthetic systems. These nanotubes have potential applications in solar cells, photocatalysis, optical sensors, and tunable multi-color light-emitting materials.
In nature, sunlight is captured by plants and photosynthetic bacteria, which then transfer the energy through a series of steps to the reaction center for storage as chemical energy. The alignment of chromophores in light-harvesting complexes and their efficient energy migration between them have attracted significant interest in understanding energy transfer processes, especially for applications involving energy conversion and storage.
To explore this direction, Dr. Supratim Banerjee from the Indian Institute of Science Education and Research (IISER) Kolkata and Dr. Suman Chakrabarty from the S. N. Bose National Center for Basic Sciences (SNBNCBS) Kolkata conducted experimental and computational investigations on artificial light-harvesting using organic nanotubes. These nanotubes were formed by combining an organic fluorescent molecule called cyano stilbenes (known for their enhanced emission in an aggregated state) with a therapeutically important biopolymer called heparin (used as an anti-coagulant during surgery and post-operative treatments) in an aqueous medium.
In the presence of heparin, the cyano stilbenes formed nanotubes with bright greenish-yellow emission through electrostatically driven co-assembly. Similar to antenna chromophores in bacterial photosynthesis, these nanotubes acted as efficient energy donors in a system mimicking natural photosynthetic processes. They transferred energy to acceptor dyes, such as Nile Red and Nile Blue, resulting in color tuning from greenish-yellow to orange-red, even producing white light. This energy transfer phenomenon, known as Förster resonance energy transfer (FRET), is crucial for various applications like determining DNA/RNA structures, mapping biological membranes, and real-time PCR tests.
The study, published in the Royal Society of Chemistry’s flagship journal, Chemical Science, investigated the formation of nanotubes using absorption and fluorescence spectroscopy, transmission electron microscopy (TEM), and fluorescence lifetime imaging microscopy (FLIM). Molecular Dynamics (MD) simulation studies revealed that the cyano stilbene molecules formed cylindrical structures in the presence of heparin. The simulation studies also visualized and quantified the local molecular interactions and packing of the cyano stilbene chromophores, leading to the formation of one-dimensional nanostructures. These light-harvesting systems demonstrated temperature responsiveness, making them suitable for use as ratiometric emission thermometers, which sense temperature based on variations in emission intensity at two different wavelengths, in the temperature range of 20–90 °C. This practical application highlights the potential of these artificial light-harvesting systems.
Publication link: Chemical Science, DOI: 10.1039/d3sc00375b
