Sensitive and quantitative probe of molecular chirality with heterodyne-detected doubly resonant sum frequency generation spectroscopy.

Abstract

Heterodyne-detected vibrationally electronically doubly resonant chiral sum frequency generation (HD-DR chiral SFG) spectroscopy has been developed for the study of chiral molecules with chromophores. The method enables us to detect and distinguish chiral molecules with high sensitivity and to obtain information on molecular vibrations. Strong enhancement due to the electronic resonance improves the sensitivity, and heterodyne detection ensures that the signal intensity is linear to the sample concentration. Detection of HD-DR chiral SFG signal from a dilute solution of binaphthol with 20 mM concentration and tens of nanometers thickness was demonstrated. Taking advantage of the enantiomer-dependent sign and linearity of the signal to the concentration, molecular concentrations and enantiomeric excesses were accurately evaluated. HD-DR chiral SFG is expected to have widespread application in the study of molecular chirality of thin films or samples of a very small quantity.