Theoretical investigation and molecular design of some azulene derivativeswith large hyperpolarizabilities

The molecular hyperpolarizabilities and electronic properties of some azule ne-containing chromophores have been investigated by employing AM1/FF and Z INDO/S-CI approaches. The calculation results show good agreement with the experimental values. It is found that the nonalternant azulene ring can be regarded as a more efficient conjugation bridge compared with benzene and t hiophene because of its lower delocalization energy. Enhanced beta values c an be obtained by extending the conjugation length, altering substituted po sitions, or choosing appropriate substituents. The 1-donor-5-acceptor-azule nes are found to have large beta values and small dipole moments (e.g., the 1-dithioylidenemethyl-5-[2,2-dicyanovinylbutadienyl] azulene has a high be ta(0) value of 181.7 x 10(-30) esu, which is close to the highest reported values and a relatively small dipole mu of 5.3 D), and the latter propertie s may be helpful in reducing chromophore-chromophore electrostatic interact ions and in optimizing the chromophore loading level and the order paramete r while incorporated into the polymer matrix.