Response theory calculations of two-photon circular dichroism

The feasibility of calculations of two-photon circular dichroism (TPA–CD) by means of response theory is demonstrated. The results from sample applications, involving the calculation of residues of appropriate frequency dependent quadratic response functions within a density functional theory model, show that the structural content of TPA–CD spectra is very different from both normal circular dichroism and two-photon absorption, indicating a unique fingerprinting functionality for chiral species. Combined with increased penetrability of the infrared exciting light and the confocal nature of two-photon absorption, this makes TPA–CD a useful tool for biomolecular identification.