Faculty Publications

Chirality-dependent two-photon absorption probabilities and circular dichroic line strengths: theory, calculation and measurement

Document Type

Article

Publication Date

August 1996

Abstract

[erratum 210(3): 515 (1996)] Theory and calculations relevant to the measurement, analysis, and interpretation of chirality-dependent two-photon absorption (TPA) properties of molecules and crystals are presented and discussed. The theory development focuses on TPA processes in which excitation is with a single, one-color beam of either left- or right-circularly polarized light, and it gives expressions that show the dependence of TPA line strengths on the circular polarization state of the exciting radiation. Three types of molecule-photon interaction mechanisms are represented in the theory, each of which makes a distinctive contribution to molecular transition polarizabilities and two-photon transition amplitudes. Two of these mechanisms assume either purely electric-dipole (μμ) or purely magnetic-dipole (mm) interaction processes in the two-photon absorption events, whereas the third mechanism assumes a combination of electric- and magnetic-dipole (μm) interaction processes. The molecular transition polarizabilities associated with μm interaction processes carry information about both the degree and sense of structural handedness in the absorbing systems and they vanish in the absence of any structural chirality. Differences between the left- versus right-circularly polarized TPA line strengths of a chiral system reflect interferences between transition amplitudes associated with μm and μμ (and/or mm) interaction processes. In this study, a model is developed for calculating the circularly polarized TPA line strengths of atomic-like chromophores in a chiral molecular or crystalline environment, and a parametrized form of this model is used to perform calculations on Gd3+ ions in single-crystal enantiomorphs of Na3[Gd(C4H4O5)3] · 2NaC1O4 · 6H2O. The results obtained from these calculations are compared to results obtained from fluorescence-detected two-photon circular dichroism (FD-TPCD) measurements reported for Na3[Gd(C4H4O5)3] · 2NaC104 · 6H2O.

Journal Title

Chemical Physics

Volume

208

Issue

2

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