Dithienylbenzene: New Switches in Photochemistry Field

Solar energy is one of the most popular ways of turning sunlight into electricity (Figure 1). The total amount of solar energy incident on earth is vastly more than the world’s current and anticipated energy requirements. In the 21^st century, solar energy is expected to become an increasingly attractive as a renewable energy source owing to its inexhaustible supply and its non-polluting character, in stark contrast to the finite fossil fuels coal, petroleum, and natural gas [1].

Figure 1. The next better world: This image is sourced from a green business guide.

This solar energy is absorbed by various instruments and devices, but one of the main challenges of solar energy is to store it efficiently, such that the energy is available when the sun is not shining. Prof. Bo Durbeej, computational physics in the Department of Physics from Linköping University, Sweden, have developed aromaticity based on a new type of molecule (Dithienylbenzene) will have the ability to capture solar energy efficiently and store it for later consumption [2]. The concept of aromaticity is first applied to electronically excited states by Dewar [3a] and Zimmerman [3b] in the 1960s to explain the formation of four-membered rings in the photochemical electrocyclization reactions. 

They have synthesized and the carried out the experimental and computational characterization of a dithienylbenzene switch where the typical non-aromatic, ethene-like motif bridging the two thienyl units, The corresponding switch in its isomeric open (1a) and closed (1b) forms, and in a closed-oxidized form (1c), are shown in (Figure 2). This molecule is called as a 'molecular photoswitches'. Photoswitches are organic or organometallic chromophores that undergo a reversible chemical transformation upon absorption of light. In other words, such a photoswitch acts like a battery that captures solar energy, stores it as chemical potential, and releases it on demand as heat [4]. These types of molecules are available in two different forms, with different properties. The chemical structures of all the photoswitches were influenced by light energy which indicates that its structures and the properties can be changed by lighting it. One possible area of application for photoswitches is molecular electronics, in which the two forms of the molecule have different electrical conductivities. Another area is photopharmacology, in which one form of the molecule is pharmacologically active and can bind to a specific target protein in the body, while the other form is inactive.

Figure 2. Chemical structures of the open (1a), closed (1b) and closed-oxidized (1c) forms of the dithienylbenzene. 

Prof. Bo Durbeej says that “Our molecule can take on two different forms: a parent form that can absorb energy from sunlight, and an alternative form in which the structure of the parent form has been changed and become much more energy-rich while remaining stable. This makes it possible to store the energy in sunlight in the molecule efficiently,”.. 

Most of the chemical reactions will start with a condition, where a molecule has high energy will subsequently pass to the one with low energy. Here, this new molecule has low energy and eventually has low energy and subsequently changes to one with the high energy”. 

The researchers will now examine that how the stored energy can be released from the energy-rich form of the molecule, in the best way and the concept of excited-state aromaticity (ESA) holds a substantial promise as a tool for designing potent electrocyclization-based photoswitches within the framework of dithienylethenes. In future research, the planning was to investigate whether this concept is fruitfully applicable and also the design of photoswitches based on other reactions and frameworks. 

References 

1. Solar Energy Book Chapter: https://www.sciencedirect.com/topics/engineering/solar-energy
2. B.Oruganti, et al., J. Am. Chem. Soc. 142, 32, 13941 (2020). 
3. a) M. J. S. Dewar, Tetrahedron, 22, 75 (1966). b) H. E. Zimmerman, J. Am. Chem. Soc. 88, 1564 (1966). 
4. C.L. Sun et al., ChemPhotoChem 3, 268 (2019).

Blog Written By

Dr. S. Chandrasekar

Institute for Advanced Study

Shenzhen University, China

Editors

Dr. A. S. Ganeshraja

Dr. K. Rajkumar

Reviewers

Dr. Y. Sasikumar

Dr. S. Thirumurugan