P. Wang et al., Theoretical investigation and molecular design of some azulene derivativeswith large hyperpolarizabilities, J PHYS CH A, 103(35), 1999, pp. 7076-7082
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.