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Contributions of Low-Lying Excited States to Optical Nonlinearities in Squaraines

Published online by Cambridge University Press:  10 February 2011

K. D. Singer ,
J. H. Andrews ,
J. D. V. Khaydarov ,
D. L. Hull  and
K. C. Chuang
K. D. Singer
Affiliation:
Case Western Reserve University, Department of Physics, Cleveland, OH 44106-7079
J. H. Andrews
Affiliation:
Case Western Reserve University, Department of Physics, Cleveland, OH 44106-7079
J. D. V. Khaydarov
Affiliation:
Case Western Reserve University, Department of Physics, Cleveland, OH 44106-7079
D. L. Hull
Affiliation:
NASA Lewis Research Center, Cleveland, OH 44135-3191
K. C. Chuang
Affiliation:
NASA Lewis Research Center, Cleveland, OH 44135-3191
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Abstract

We measured the third-harmonic spectrum for a series of both centrosymmetric and noncentrosymmetric squaraine dyes in chloroform. By fitting the experimental dispersion of the third order susceptibility, γ, to a four-level sum-over-states model, we determined the strength and location of the lowest lying two-photon-like transition. In each case, we find that the lowest two-photon-like state appears just above the dominant linear absorption peak in energy and that the transition moment to that state makes a significant contribution to the nonlinearity, as do transition moments to one or more higher-lying two-photon-like states in the ultraviolet. The spectra of one centrosymmetric dye contains an additional feature evidencing a nonzero dipole moment difference between the ground and first excited state dipole moments (δμ) that we attribute to a conformational asymmetry. A noncentrosymmetric squaraine dye shows a similar feature, which, as expected, arises from its δμ. Effects of symmetry breaking are described.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 413: Symposium W – Electrical, Optical, and Magnetic Properties of Organic Solid State Materials III , 1995 , 215
Copyright
Copyright © Materials Research Society 1996

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References

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