Probing Structure-Property Relationships in Third-Order Nonlinear Optical Polymers: Third Harmonic Generation Spectroscopy and Theoretical Modeling of Systematically Derivatized Conjugated Aromatic Polyimines
Abstract
Picosecond third harmonic generation (THG) spectroscopy in the range 0.9-2.4 microns (0.52-1.38 eV) combined with sum-over-states (SOS) theoretical modeling have been used to investigate the third-order nonlinear optical properties of a series of 9 conjugated aromatic polyimines designed to elucidate structure- Chi(3) relationships in conjugated polymers. The TMG-measured frequency dispersed third-order susceptibility Chi(3) of the series of polymers has off-resonant and three-photon resonance-enhanced values in the range of 1.1x10(exp -12) to 2.0x10(exp -11) esu and 6.4x10(exp -12) to 7.2x10(exp -11)esu, respectively, demonstrating a large modulation of nonlinear optical response by simple structural variations. A random copolymer was found to have enhanced Chi(3) compared to either of its parent homopolymers. Asymmetric donor side-group substitutions was found to result in 7-10-fold enhancement of off-resonant Chi(3) compared to either symmetric substitutions or no substitutions. Theoretical three and four-level SOS models, justified by site-selective fluorescence spectroscopy, were found to describe the Chi(3) dispersion data and the observed multiphoton resonances very well. The zero- frequency Chi(3) was predicted from the SOS models to be negative for eight of the nine polymers and to be in the range of -0.43 to 8.12x10(exp -12) esu, the magnitudes of which are very close to observed off-resonance values at 2.4 microns (0.52 eV). Negative real part of Chi(3)(-omega; omega,-omega, omega) over a wide wavelength range of(Lambda>1.38 microns) was also predicted by the SOS Models for the same eight polymers with strong one-photon and two-photon resonances, suggesting that they would exhibit self-defocusing phenomena.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 16, 1998
- Accession Number
- ADA356421
Entities
People
- Chen-jen Yang
- Herman Vanherzeele
- Jeffrey S. Meth
- Samson A. Jenekhe
Organizations
- University of Rochester