Development and investigation of novel norbornadiene and anthracene derivatives for efficient photochemical (sun)light energy conversion and storage

• Applicant: Professor Dr. Heiko Ihmels
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 563533943

The development of methods for the conversion, storage and release of energy from sustainable sources is one of the most important and urgent scientific and social challenges. In this context, the exploitation of sunlight is an attractive goal because the sun is an inexhaustible and powerful source. Hence, effective methods have been established and are already applied in practice to use the energy of solar radiation. However, depending on the location and the purpose of use, application-specific conditions for energy storage, transport, and release have to be met. Therefore, it is still necessary to develop alternative solar energy storage systems that complement or optimize the existing ones. In this context, this research project will focus on the promising approach towards conversion and storage of solar light energy as chemical energy by means of a photochemical reaction, usually termed molecular solar thermal energy storage (MOST). This method utilizes photoactive compounds that are converted into photoproducts with higher energy upon absorption of (sun)light. This reaction is fully reversible, so that the stored chemical energy can be released in turn as heat in a triggered back reaction. In line with this approach, the light-induced reversible formation of high-energy photoproducts of norbornadiene and (azonia)anthracene derivatives will be further developed and optimized in this project. Based on our own studies in this field, the main scientific goal is to identify those structural factors providing an optimal balance between the key parameters of photochemical energy conversion, storage and release. The knowledge gained will be used to develop new generations of efficient molecular energy storage systems. Although the underlying photochromic reactions are known as MOST systems already, there is still room for improvement. Specifically, the following aspects have not yet been investigated comprehensively and will be addressed in detail: The energy storage density of norbornadiene derivatives should be improved by i) systematic removal of redundant fragments from the target molecule, ii) or by integration of as many norbornadiene units as possible into one molecule. As there is still demand for MOST systems with a reliable and efficient energy-releasing back reaction, the photoinduced electron transfer reaction will be systematically investigated as an efficient route, that may be triggered by light with high local and temporal control. The reversible [4+4] photocycloaddition of anthracene and benzo[b]quinolizinium derivatives for the conversion and storage of sunlight has been surprisingly neglected in this field, so far. Therefore, this class of reactions will be extensively explored as basis for MOST systems for the first time because it provides several favorable properties for an efficient and robust conversion and storage of sunlight energy.

• DFG Programme: Research Grants