First hyperpolarizabilities of 1,3,5-tricyanobenzene derivatives: origin of larger beta values for the octupoles than for the dipoles.
A series of donor-acceptor substituted stilbene and diphenylacetylene derivatives and their octupolar analogues have been synthesized and the linear and nonlinear optical properties (beta) studied by both experiments and theoretical calculation. The lambda(max) of the dipoles increases with the conjugation length and is always larger when the C=C bond is used, instead of the C[triple bond]C bond, as the conjugation bridge. Although the lambda(max) values of the octupoles show no clear trend, they are much larger than those of the dipoles. The beta(0) values of the dipoles increase with conjugation length and as the conjugation bridge is changed from the C[triple bond]C to C=C bond. This increase is accompanied by an increase in either lambda(max) or the oscillator strength. Similarly, the beta(0) values of the octupoles increase with the conjugation length and with a change in the donor in the order: NEt2 < N(i-amyl)Ph < NPh2. Moreover, beta(yyy)/beta(zzz) ratios are in the range of 1.6-3.9 and decrease with the conjugation length. Beta values calculated by the finite-field and sum-over-states methods are in good agreement with the experimental data. Also, there is a parallel relationship between the calculated beta values and bond length alternation (BLA). From these results, the origin of the larger beta values for octupoles than for dipoles is assessed.
Lee
Sang Hae
SH
Molecular Optoelectronics Laboratory, Department of Chemistry and Center for Electro- and Photo-Responsive Molecules, Korea University, 1-Anamdong, Seoul, 136-701, Korea.
Park
Jo Ryoung
JR
Jeong
Mi-Yun
MY
Kim
Hwan Myung
HM
Li
Shaojun
S
Song
Jongwon
J
Ham
Sihyun
S
Jeon
Seung-Joon
SJ
Cho
Bong Rae
BR