Characterization of intensity-dependent optical rotation phenomena in chiral molecules in solution

Abstract

The rotation of the plane of polarization of linearly polarized light by chiral molecules in solution is due to a forward scattering event. Ordinary optical rotation, a single-photon effect, is independent of intensity. As the light intensity is increased, other effects can appear, such as two-photon scattering or alignment of the molecule by one photon and scattering with a change of polarization by another. Both of these effects result in intensity-dependent (or nonlinear) optical rotation. A polarimeter was used to measure the nonlinear optical rotation of solutions in a heterodyne experiment. No nonlinear optical rotation was found in molecules lacking an absorption band near the laser frequency. In the three pyrimidine nucleosides studied, which do have such an absorption band, a nonlinear optical rotation was identified that was cumulative with each laser pulse. The effect persisted with a time constant that was on the order of seconds and characteristic of the molecule.

Theory, calculation and observation of nonlinear optical activity in chiral molecules

“…Cameron and Tabisz 46 went on to refine their experiment with the introduction of a known, modulated rotation of the polarization direction of the light. The modulated rotation mixed with the optical rotation due to the chiral solution, giving a term in the transmitted irradiance that is modulated at the same frequency and proportional to the product of the two rotations.…”

Two-Photon Polarization Dependent Spectroscopy in Chirality: A Novel Experimental-Theoretical Approach to Study Optically Active Systems

“…During the last decade, nonlinear optics have opened a new path in this direction. Processes such as sum-frequency generation (SFG) [ 16 ], second harmonic generation (SHG) [ 17 , 18 ], and nonlinear optical activity (NOA) [ 19 , 20 ], including multiphoton optical rotation [ 21 , 22 , 23 , 24 , 25 ], have been reported, experimentally and theoretically, for the study of chemical and biological chiral systems. Although, the development of these novel nonlinear optical approaches has been an important piece to solving the puzzle, truly polarization dependent multiphoton absorption processes (two-photon absorption) were experimentally unrevealed until our recent development of the double L-scan technique [ 26 ].…”

“…Hitherto, measuring TPACD in chiral molecules has represented a major challenge to scientists in the field, mainly because the dichroism is determined by the small contribution of the transition magnetic-dipole and electric-quadrupole transition moments [ 27 , 28 ]. Experiments using pump-probe, [ 19 ], intensity dependent multiphoton optical rotation [ 25 ], resonance-enhanced multiphoton ionization [ 40 , 41 ] and polarization modulation single beam Z-scan [ 42 ] have been attempted. Although all these experimental approaches were clever, none of them has been capable to fully reveal pure TPACD, and even more important, to produce a definite TPACD spectrum of any substance.…”