Scaling law for second-order hyperpolarizability in poly(triacetylene) molecular wires.
Poly(triacetylenes) are rodlike molecules with electrons delocalized over a one-dimensional path. We show that they exhibit a power-law dependence of the second-order hyperpolarizability gamma on the monomer unit n for short molecules and a smooth saturation toward a linear increase in longer molecules. The power law of gamma?n(a) with a approximately 2.5 from dengenerate four-wave mixing and third-harmonic generation measurements is in good agreement with quantum-chemical calculations. The critical conjugation length for saturation in the three cases is shown to be approximately 60 carbon-carbon bonds, which indicates the upper boundary for the electron delocalization in such a one-dimensional molecular wire.
Gubler
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U
Nonlinear Optics Laboratory, Institute of Quantum Electronics, Swiss Federal Institute of Technology ETH, ETH Hönggerberg, CH-8093 Zürich, Switzerland.
Bosshard
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C
Günter
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P
Balakina
M Y
MY
Cornil
J
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Brédas
J L
JL
Martin
R E
RE
Diederich
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F