Ionic [arene-Fe-Cp](+) fragments were used as electron accepters in combina
tion with dimethylamino or pyridoneiminyl donors to form push-pull substitu
ted chromophores. While a tolane derivative showed high second-order non-li
near optical activity (measured by hyper-Rayleigh scattering), an analogous
pyridoneimine derivative did not. With the help of an X-ray crystal struct
ure analysis this discrepancy was traced back to a cyanine-like structure o
f the imine. Semiempirical INDO/S calculations support this conclusion. (C)
1999 Elsevier Science S.A. All rights reserved.