(Invited) Emergent Chiroptical Properties in Assembled Molecules and Materials: From Native Chirality to Global Chirality

Abstract

The emergence of chiroptical properties in molecules and materials through their asymmetric organizations has fascinated humankind in general and the scientific community in particular. By adopting molecules, plasmonic systems, and semiconductor quantum dots as examples, the translation of ‘local’ chirality in these building blocks to the ‘global’ chirality when they self-assemble as nanoobjects will be explained. The presentation covers the following aspects. In assembled molecular systems, induced circular dichroism (ICD) originates through the off-resonance coupling of transition dipoles, resulting in monosignated CD signals. In contrast, exciton-coupled circular dichroism (EC-CD) originates through the on-resonance exciton coupling, displaying bisignated CD signals.1-3 Bisignation in the CD responses of assembled plasmonic systems results from the resonant plasmon coupling, termed surface plasmon-coupled circular dichroism (SP-CD).4,5 The presentation will draw parallels between the emergence of EC-CD and SP-CD based on the coupling of their transition dipoles.3 More importantly, our studies have concluded that the sign of the EC-CD/SP-CD depends not only on the handedness of the assembly but also on the sign of the interaction energy between the neighboring dipoles.6 The presentation will also discuss how chiral surface domains of various self-assembled amino acid-based templates transfer chiral information to bound achiral chromophores. The origin of CD and CPL of achiral molecules on these templates are explained based on exciton coupling.7 The presentation will also provide fundamental insight into the interaction of chiral molecules with silicon nanoparticles and the emergence of its CD and CPL.8 An open challenge is to develop a universal model which can explain the chiroptical properties of assembled systems based on the transition dipolar coupling and interaction energy: our findings in this direction will be presented. Thomas R, Kumar J, George J, et al. Phys. Chem. Lett., 2018, 9, 919-932.Kar S, Swathi K, Sissa C, et al., Phys. Chem. Lett., 2018, 9, 4584-4590.Nizar NSS, Sujith M, Swathi K, et al. Soc. Rev.,2021, 50 , 11208-11226.George J, Thomas KG, J. Am. Chem. Soc. 2010, 132, 2502-2503.George J, Kar S, Anupriya ES, et al. ACS Nano 13, 2019, 4392-4401.Swathi K, Sissa C, Painelli A, et al. Commun. , 2020 , 56, 8281-8284.Somasundaran SM, Kompella SVK, Mohan TMN, et al. ACS Nano 2023 17, 11054-11069.Sujith M, Vishnu EK, Sappati S, et al. J. Am. Chem. Soc. , 2022, 144, 5074-5086. The theoretical collaborations with Dr. R. S. Swathi, IISER Thiruvananthapuram (India), Dr. Cristina Sissa and Prof. Anna Painelli, University of Parma (Italy), and Prof. S. Balasubramanian, JNCASR, Bangalore are greatly acknowledged. KGT acknowledges the J. C. Bose National Fellowship and Nanomission project (DST/NM/TUE/EE-01/2019), the Department of Science and Technology, Government of India, for financial support.