Aromaticity, nonlinear optics, molecular

Phthalocyanines 244 and hemiporphyrins 245 and 246 are aromatic systems. Extended conjugation confers special properties to these molecules that make them building blocks for new molecular organic materials with useful electric and nonlinear optical applications (Scheme 85).288... 

In guest/host PR polymers the macroscopic nonlinear optical properties result from the molecular constants of the dopant molecule (also called dinmiophore). Chromophores for nonlinear optical properties are usually based upon aromatic ra-electron systems unsymmetrically eiid-capped with electncm donat and electron accepting groups, as shown in Fig. 3. The molecular polarization of such molecules is a nonlinear fonction of the electric field and can be simplified to (4,5) ... 

Quantum mechanical analysis based on a simple two-level model [22] and bond-order alternation (BOA) principle exploiting aromaticity [23] have worked surprisingly well in providing useful structure/property relationships for the design of chromophores with ever improving molecular hyperpolarizability. Table 1 provides some representative examples with improved molecular optical nonlinearity developed over the past decade. It has been shown that very large nonlinearities... 

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