Nonlinear optical response of cofacial phthalocyanine dimers and trimers
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122 (United States)
- Chemistry Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439 (United States)
The effects of intermacrocycle interactions on the second hyperpolarizabilities {l_angle}{gamma}({minus}{omega};{omega},{minus}{omega},{omega}){r_angle} of cofacial phthalocyanine dimers and trimers are studied. A theoretical analysis is presented based on the Frenkel exciton model for a chain of three level molecules. Using a simplified analysis in the static and near-resonant regimes we identify two mechanisms which lead to enhancements in the dimer or trimer value of {l_angle}{gamma}({minus}{omega};{omega},{minus}{omega},{omega}){r_angle} over that of the monomer. The first mechanism is a disruption of the balance between type I and type II terms in the sum over states expression for the second hyperpolarizability tensor {gamma}{sub kjih}({minus}{omega};{omega},{minus}{omega},{omega}), caused by weak intermacrocycle interactions. The second is a near-resonance enhancement of the type II terms due to an intermacrocycle interaction induced shift in the monomer derived two-photon allowed states towards twice the laser photon energy. This analysis is in good agreement with recent degenerate four wave mixing experiments [SPIE Proc. {bold 2527}, 61 (1995)] which showed a strong enhancement of {l_angle}{gamma}({minus}{omega};{omega},{minus}{omega},{omega}){r_angle} for SiPcO oligomers as a function of the number of macrocycles. Our calculations suggest that the first mechanism is responsible for the 25-fold monomer to dimer enhancement measured in this system, and that the additional 4-fold enhancement found in going from the dimer to the trimer is primarily the result of the second mechanism. {copyright} {ital 1997 American Institute of Physics.}
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 549298
- Journal Information:
- Journal of Chemical Physics, Vol. 107, Issue 3; Other Information: PBD: Jul 1997
- Country of Publication:
- United States
- Language:
- English
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