Charge-transfer complexation: A highly effective way towards chiral nanoparticles endowed by intrinsically chiral helicene and enantioselective SERS detection

Abstract

An ordered chiral gold nanoparticle (AuNPs) array was prepared by the treatment of achiral sphere-shaped gold nanoparticles endowed with electron-accepting dinitro-phenyl (DNP) groups complexing with enantiomers of [6]helicene representing electron donors with strong chiroptical properties. Such surface-functionalization utilizes the principles of charge-transfer (CT) interaction. The incorporation of [6]helicene molecules with unique electronic and optical properties and subsequent arrangement of AuNPs caused chirality induction to intrinsically non-chiral plasmon-active nanostructures. The created nanostructures enabled the excitation of chiral plasmon and its application in highly sensitive enantioselective detection of small chiral molecules by surface-enhanced Raman spectroscopy (SERS). The chiral plasmonic response of such a system was shown to be fully controlled via the helicity of the parent [6]helicene. Upon calibration, it allowed us to directly determine the enantiomeric composition of non-racemic mixtures of (R)/(S)− 1-phenylethanol and (R)/(S)− 2-butanol.