摘要
Sum-frequency vibrational spectroscopy (SFVS) has recently been considered a potentially useful tool for probing chirality. In contrast to conventional chiral probes, SFVS has the advantage of being electric-dipole allowed. Up till now, it has been applied only to probing of vibrational chirality in chiral liquids. We report here the first application of the technique to probe vibrational chirality in chiral polymer films. The polymer used has a pi-electron conjugated structure in the main chain, and a chiral center in the side chains that is close to the main chain. Interaction between the chiral side chains and the main chain presumably causes the main chain to twist helically. The vibrational modes probed are stretches associated with the main chain. As expected for chiral responses, we find that the chiral SFVS spectra are identical for the two enantiomers, and the signal vanishes for the racemic polymer. We also confirm experimentally that the chiral nonlinear succeptibilities for SFVS for the two enantiomers have opposite signs. The chiral SFVS spectra of the polymer are relatively strong due to near-resonance enhancement since the visible input is close to the first electronic transition band of the conjugated main chain.