| Abstract
| - Six permutations of 4-fold donor and/or acceptor substitution of paracyclophane at the 4, 7, 12,and 15 positions were synthesized to probe the phenomenon of three-dimensional delocalization on thenonlinear optical properties of organic materials. The interplay between through-bond intramolecular chargetransfer (ICT) as well as three-dimensional, or through-space, ICT processes gives rise to large quadratichyperpolarizability values. The determination of dipolar (βJ=1) and octupolar (βJ=3) irreducible tensorcontributions to the overall β tensor value is made possible by the polarized harmonic light scatteringtechnique at 1.32 μm. The electric field-induced second-harmonic generation technique was also used at1.91 μm for comparison. Significant experimental β values for members of the series made of twocentrosymmetric benzene-like units are a clear signature of a purely through-space ICT between two arylsubunits. The two configurational isomers that pair two dipolar donor−acceptor chromophores also exhibitoctupolar character. Analysis of these two with an additive model for βJ=1 and βJ=3 reveals a strong three-dimensional inter-ring charge transfer.
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