Metal‐Free Supramolecular Xerogels for pH‐Programmed Inversion of Chiral Raman Discrimination

ABSTRACT

pH‐programmed supramolecular materials that provide selectable chiral Raman responses are of interest for adaptive chemical sensing. Herein, we report imidazole‐ and indole‐functionalized organic xerogels as metal‐free, Raman‐active substrates for enantioselective recognition. By varying the aromatic π‐core and imidazole substitution topology, C8indole4imi was identified as the most responsive scaffold. Separately prepared acidic and alkaline xerogel specimens displayed distinct assembly states and opposite ibuprofen discrimination polarities. The pH 2.0 xerogel exhibited a heterogeneous ribbon/fiber‐rich assembly and favored R‐ibuprofen (discrimination index, DI = −0.318), whereas the pH 12.0 xerogel formed a finer and more continuous fibrillar network and favored S‐ibuprofen (DI = +0.454). Morphology, rheology, Fourier‐transform infrared spectroscopy (FTIR), density functional theory (DFT), and host‐packing molecular dynamics (MD) analyses are consistent with pH‐dependent changes in the supramolecular recognition environment; the simultaneous change in ibuprofen ionization is also expected to contribute. The principal advance is therefore the pH‐programmed inversion of chiral Raman discrimination in a metal‐free supramolecular xerogel platform; same‐specimen switching and a quantitatively validated enhancement mechanism are not claimed.