Three octopolar molecules

Prior to discussing the properties of octopolar molecules, it is instructive to consider first some of the basic properties of tensors. In general, any tensor of rank n can be decomposed in a sum of so-called irreducible tensors that are invariant under three-dimensional rotation [99] ... 

For the hyperpolarizability of purely octopolar molecules, all irreducible tenso-rial components of weight strictly lower than three cancel due to symmetry requirements and P = P [99]. For other molecules, the hyperpolarizability can contain contributions of all irreducible tensor components, depending on the symmetry of the molecule. 

The area of molecular nonlinear optics has been rejuvenated by efforts to investigate three-dimensional multipolar systems, functionalized polymers as optoelectronic materials, near infrared optical parametric oscillators and related aspects.71 There have been some advances in chromophore design for second-order nonlinear optical materials 72 these include onedimensional CT molecules, octopolar compounds and organometallics. Some of the polydiacetylenes and poly(/>-phenylenevinylene)s appear to possess the required properties for use as third-order nonlinear optical materials for photonic switching.73... 

Some examples of intuition-based or modeling-based advances in nonlinear properties, specifically the first hyperpolarizability response p, have been developed in the past three decades. These include the bond-length alternation motif, the idea of octopolar molecular structures, the stronger responses of excited states and the use of purposely twisted -ir-electron molecules to modify the admixture of quinoid and aromatic structures. 

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