Influence of N-substitution on the properties of Bicyclooctadiene/ Tetracyclooctane photoswitch for Molecular Solar Thermal Energy Storage Akanksha Sangolka, Mohmmad Faizan, K Rama Krishna and Ravinder Pawar National Institute of Technology, Warangal, India Molecular photoswitching couples have potential to harvest and store the inexhaustible solar radiation in the form of chemical energy and release thermal energy when desired. 1 Thus, the suitable photoswitching systems promises to meet the increasing energy demand of the modern society in a sustainable manner. 2 The photochromic couple known till date does not exhibits all the features essential for practical application of molecular solar thermal energy storage (MOST). 3 En route to incorporate all the desired properties, rational designing and engineering of photoswitching system is of utmost importance. 4 Herein, the effect of N-substitution on the properties of Bicyclooctadiene/Tetracyclooctane (BOD/TCO) photoswitching couple for its MOST applications has been systematically analysed using the ω B97X-D/6-311++G** and results are verified with DLPNO-CCSD(T)/def2TZVP level of theory. Outcomes of the study exclusively emphasizes that the position of N substantially influences the properties of the photoswitching system. Substituting the unsaturated C with N increases the storage density and photophysical properties while the presence of N at the bridgehead position increases the barrier for thermal back conversion reaction. The substitution of aza-BOD/TCO system considerable increases the storage energy and a remarkable increment in the molar extinction coefficient is also observed. An approximately 32–109 nm red-shift in the first excitation wavelength is noticed upon substitution of various aza-BOD and aza-TCOs. The best studied photochromic system has storage energy of 200.36 kJ/mol, storage density of 0.84 MJ/kg, and a thermal back reaction barrier of 168.56 kJ/mol. Moreover, the difference of 82.79 nm is obtained between the first excitation wavelength of its aza-BOD and aza-TCO. Solvation of the aza-BOD/TCO photoswitching systems appreciably alters their thermochemical and photophysical properties. The aza-BOD/TCO couples displays better properties in Toluene than the high polarity solvents. The outcomes of this work would indeed be advantageous to design a novel molecular structure for practical MOST application in future.
References 1. J. Orrego-Hernández, A. Dreos and K. Moth-Poulsen, Acc. Chem. Res. , 2020, 53 , 1478–1487. 2. Z. Wang, P. Erhart, T. Li, Z.-Y. Zhang, D. Sampedro, Z. Hu, H. A. Wegner, O. Brummel, J. Libuda, M. B. Nielsen and K. Moth- Poulsen, Joule , 2023, 5 , 3116–3136. 3. Z. Wang, H. Hölzel and K. Moth-Poulsen, Chem. Soc. Rev. , 2022, 51 , 7313–7326. 4. A. A. Sangolkar, M. Faizan, K. R. Krishna and R. Pawar, Mol. Syst. Des. Eng. , , DOI:10.1039/D2ME00274D.
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