Design of novel nonlinear optical chromophores with multiple substitutions
The molecular first hyperpolarizabilities (β) and electronic properties of some tetra-substituted benzenes/pyrazines which can be described as 1,2-didonor-4,5-diacceptor-benzenes/2,3-didonor-5,6-diacceptor-pyrazines have been investigated by employing an AM1/FF and ZINDO/S-CI approach. It is found that these multiple substituted chromophores possess large β values which may be attributed to the positive contribution of the off-diagonal tensorial component βxyy. Two novel chromophores (1 and 2) containing lengthened conjugation and thermally stable imidazole rings are designed under such a multiple substitutions principle. Chromophore 1 shows a very large µβ0 value of approximately 3900×10-48 esu.† The theoretical calculation and preliminary experimental results indicate that a good nonlinearity–transparency–thermal stability trade-off is achieved for chromophore 2, which possesses a µβ0 of 555×10-48 esu, a rather blue-shifted absorption peak at 384 nm in THF and a high decomposition temperature (Td) of 377°C.