Nuclear Spin Singlet States in Photoactive Molecules: From Fluorescence/NMR Bimodality to a Bimolecular Switch for Spin Singlet States

Abstract

Nuclear spin singlet states are silent states in nuclear magnetic resonance (NMR). However,t hey can be probed indirectly and offer great potential for the development of contrast agents for magnetic resonance imaging (MRI). Introduced here are two novel concepts:F irstly,t he bimodal NMR/fluorescence properties of 13 C 2 -tetraphenylethylene.I t possesses al ong-lived singlet state in organic solvents,a nd it shortens upon the addition of water.T his simultaneously increases the aggregation-induced emission (AIE) of the molecule,r esulting in as ubstantial enhancement of fluorescence.Secondly,introduced is abimolecular switch for singlet states based on 3-2 H-coumarin containing an isolated proton. Upon UV-light exposure,adimer forms,leading to acoupling between two previously isolated protons.Anuclear spin singlet state can nowb ep opulated. Excitation with aw avelength of 254 nm results in partial ring cleavage of the molecule backto its monomer.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.