Tetra-substituted azulenes

Wang et al have used the AMl/FF approach for static properties and ZlNDO/SCl to study the -hyperpolarizabdity of some azulene derivatives. High values are obtained and it is concluded that the azulene ring is a more efficient conjugation bridge between donor and acceptor than either benzene or thiophene. They use the same methods in a study of push-pull polyenes containing nonaromatic cycfic olefines and for tetra-substituted benzenes and pyrazines. 

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