The linear and nonlinear optical properties of organometallic chromophoresderived from ferrocene, [Fe-2(eta(5)-C5H5)(2)(CO)(2)(mu-CO)(mu-C-CH3())1](+)[BF4](-) and terthienyl spacers. Crystal structure of 2-[(E)-2-ferrocenylethenyl]-5-(2-thienyl)thiophene

Several chromophores based on ferrocene, [Fe-2(eta (5)-C5H5)(2)(CO)(2)(mu - Co)(mu -C-CH3)](+) and terthiophene or dithienylbenzo[c]thiophene have been synthesized. Both thienyls have been shown to act as good donor end groups in their own right but contrary to our expectations the benzo[c]thiophene merocyanine has a lower hyperpolarizablity (344 x 10(-30) esu) than its thi enyl congener (650 x 10(-30) esu). The structure of 2-[(E)-2-ferrocenylethe nyl]-5-(2-thienyl)thiophene has been determined by single crystal X-ray dif fraction. The terminal thienyl (thp) group is disordered over two orientati ons about the bithienyl C(sp(2))-C(sp(2)) bond such that the two sulfur ato ms in either thp ring are positioned trans/cis in the ratio 0.628(4):0.372( 4). The integrity of the alkenyl -C=C- remains with a bond length of 1.332( 2) Angstrom and the -C-C- lengths adjacent are 1.453(4)/1.441(4) Angstrom. Twisting of the rings from planarity occurs along the Fc-C=C-(thp)-(thp) ax is: the angle which the ethenylthiophene -C=C-C4H2S moiety makes with the C 5H4 is 11.2(2)degrees, and with the major orientation of the disordered ter minal thienyl group, 16(1)degrees. (C) 2001 Elsevier Science B.V. All right s reserved.