India has an ambitious target of achieving 300 GW of solar power by 2030. Conventional methods for producing solar power involve absorbing sunlight by a molecule and converting it directly into electricity. This is possible only during the daytime when sunlight is available. An interesting and complementary prospect is storing the absorbed solar energy by converting it into a different form of energy, such as chemical energy, which can then be transformed into electrical energy when sunlight is not available during the night-time.

To realise this prospect, Assistant Professor Dr Baswanth Oruganti from the Department of Chemistry has designed a molecule that can absorb solar energy and convert it into the chemical energy of the bonds. His paper titled Modulating the Photocyclization Reactivity of Diarylethenes through Changes in the Excited-State Aromaticity of the π-Linker has been published in the Journal of Organic Chemistry, on Cover Page, with an impact factor of 4.2. He is both the first author as well as the corresponding author of the article. For this project, he has collaborated with Prof Bo Durbeej, Division of Theoretical Chemistry, Department of Physics, Chemistry, and Biology (IFM), Linköping University, Sweden.

Abstract

In recent years, the concept of excited-state aromaticity and its applications in photophysics and photochemistry has attracted considerable research interest. Our study uses quantum chemical calculations to systematically investigate if the photocyclization reactivity of diarylethene switches can be controlled by the excited-state aromaticity of the ethene bridge. Indeed, we demonstrate that these switches can be transformed from being highly reactive to completely non-reactive by changing the excited-state character of the bridge from anti-aromatic to aromatic.

Generally, molecules tend to move from a high-energy state to a low-energy state, as the lowering of energy increases the stability of the molecule and makes it chemically less reactive. In contrast, the present study shows that it is possible to chemically transform a molecule from a low-energy (aromatic) state to a high-energy (non-aromatic) state by absorption of light. This reaction occurs via a high-energy (anti-aromatic) electronically excited state of the molecule induced by light and has potential applications for storing solar energy in the form of chemical energy.

One challenge in the design of molecular solar energy storage systems, such as the diarylbenzene designed in the study, is that it is difficult to store solar energy for a longer period due to the instability of the newly formed chemical bonds at room temperature. To store solar energy for a longer period, one needs to compromise on the amount of energy stored in the bonds. In this regard, in the future, researchers are planning to optimise their molecular design by finding the right balance between the amount of solar energy stored and the time period for which it can be stored.

The Department of Chemistry is glad to announce that Dr Nimai Mishra, Assistant Professor, along with his research group comprising PhD scholars, Syed Akhil, Manoj Palabathuni, Subarna Biswas, Rahul Singh, have published an article titled Highly-Stable Amine-Free CsPbBr3 Perovskite Nanocrystals for Perovskite-Based Display Applications in the  journal ACS Applied Nano Materials published by the American Chemical Society, having an impact factor of 6.14.

Colloidally synthesised cesium lead halide (CsPbX3; X=Cl, Br, and I) perovskite nanocrystals (PNCs) often suffer from poor ambient and environmental stability conditions, limiting their practical applications. The commonly used surfactant oleylamine is converted to oleylammonium cation, which pulls out the halide anion from the PNCs surface, thus disrupting the nanocrystal’s structural integrity and stability.

The research group has developed a simple, completely amine-free colloidal synthesis with a hot injection method in open-atmospheric conditions and introduced bromooctane as a bromine precursor to overcome the above issues. These, as synthesized amine-free PNCs, showed a photoluminescence quantum yield (PLQY) of around 60 %, and the size of PNCs is ~25 nm. Moreover, these amine-free PNCs were highly stable in the colloidal solution and thin films for more than five months in ambient conditions, with 66% of its initial PLQY.

In addition, these PNCs have shown exceptional stability under different environmental conditions, with 44 % of initial PL even after 6 hours of water treatment and 28 % of initial PL under ethanol treatment for 120 minutes. Furthermore, it has exhibited excellent photostability for 96 hours and retained 36 % of its initial PL under ceaseless UV light irradiation at 365 nm (8 W/cm2). Additionally, these PNCs have good stability upon heat treatment and maintained 34 % of initial PL upon heating up to 90 ºC.

The research team has also successfully fabricated the green-emitting down-conversion LED using these amine-free PNCs. Thus, they visualize that these amine-free CsPbBr3 PNCs are perhaps the ideal candidates for perovskite-based display applications.

Read the full paper

Dr Rajapandiyan Panneerselvam, Assistant Professor, Department of Chemistry, and his team have developed a method using a portable Raman spectrometer to quickly identify six common pathogenic Vibrio species that can contaminate seafood. His latest research paper Intelligent convolution neural network-assisted SERS to realise highly accurate identification of six pathogenic Vibrio, has been published in the Q1 Nature Index journal Chemical Communications, having an Impact Factor of 6.0.

By using gold-silver nanoparticles, the study was able to accurately detect these harmful microorganisms. The new deep learning model called a convolutional neural network (CNN), outperformed traditional machine learning methods with a classification accuracy of 99.7%. The entire identification process only took 15 minutes. The researchers also discovered that the Raman signals emitted by Vibrio species are similar to signals from certain substances found in purine degradation, such as uric acid and adenine. This knowledge helps them explain why different Vibrio species produce slightly different Raman signals. Overall, the CNN-assisted Raman spectroscopy method offers a fast and accurate way to diagnose and identify harmful microorganisms responsible for food contamination.

Abstract

The utilisation of label-free Surface-Enhanced Raman Spectroscopy (SERS) technology enabled a comprehensive analysis of the connection between Raman signals emitted by pathogenic Vibrio microorganisms and purine metabolites. Through extensive research, a sophisticated Convolutional Neural Network (CNN) model was developed, demonstrating exceptional performance with an accuracy rate of 99.7% in the rapid identification of six common pathogenic Vibrio species within a mere 15-minute timeframe. This breakthrough offers a groundbreaking approach to pathogen identification, introducing a novel and efficient method to the field.

Practical Implementation of the Research

The practical implementation of label-free SERS technology combined with a deep learning CNN model enables rapid and accurate identification of pathogenic Vibrio microorganisms. This has important social implications, including improving public health and safety by quickly identifying and controlling outbreaks, enhancing food safety measures, and enabling real-time pathogen detection in resource-limited areas. The method’s speed and accuracy contribute to more informed decision-making, mitigating the spread of infectious diseases and ultimately creating a safer society.

Future Research Plans

Moving forward, future work in the field of label-free SERS technology for pathogen identification could focus on expanding the coverage to include a wider range of Vibrio species, increasing the diversity of the dataset used for training, conducting rigorous cross-validation and external validation studies, exploring integration with portable SERS devices for on-site detection, optimising the deep learning model for speed and efficiency, and investigating clinical and environmental applications. By pursuing these avenues, the research can further enhance the versatility, reliability, and real-world applicability of the method, leading to improved methods for rapid and accurate pathogen identification in various domains.

Collaborations

• Dr Jianfeng Li (College of Materials, State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, College of Energy, School of Aerospace Engineering, Xiamen University, Xiamen 361005, China)
• Dr Lin Zhang (State Key Laboratory of NBC Protection for Civilian, Beijing 102205, China)
• Dr Zehui Chen (Xiamen City Center for Disease Control and Prevention, Xiamen 361005, China)