Cyclic siloxanes conjugated with anthracene (D4An) and pyrene (D4Py) were prepared via Heck coupling reactions of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane with 9-bromoanthracene and 1-bromopyrene, respectively. These materials exhibited solvent-dependent fluorescence with the largest Stokes shift of up to ∼146 nm, confirming the presence of intramolecular exciplex formation among the fluorophores within a cyclic siloxane. After reacting with fluoride ions, blue-shifted emissions of D4An and D4Py in organic solvents were observed; it suggests an increase in monomer emission as a result of exciplex preclusion via Si–F bond formation. Moreover, the colorless solutions of D4An and D4Py in THF turned pink and orange, respectively, in the presence of excessive F, which also suggested the formation of charge-transfer complexes. The interactions between cyclic siloxanes and fluoride ions were also studied via FTIR, ESI-MS and NMR experiments. Computational modeling studies revealed that fluoride played an important role in distorting the geometry of cyclic siloxanes by interrupting excimers of fluorescent aromatic rings in the side-chain.


“Cyclic siloxanes conjugated with fluorescent aromatic compounds as fluoride sensors” Prigyai, N.; Chanmungkalakul, S.; Thanyalax, S.; Sukwattanasinitt, M.; Ervithayasuporn, V. Mater. Adv., 2020, 1, 3358-3368.