Ferrocenyl D-π-A chromophores containing 3-dicyanomethylidene-1-indanone and 1,3-bis(dicyanomethylidene)indane acceptor groups

The nonlinear optical properties of ferrocenyl (Fc) D-π-A chromophores containing powerful 3-dicyanomethylidene-1-indanone (2) and 1,3-bis(dicyanomethylidene)indane-based acceptor group (3) have been measured by EFISH technique at 1.907 μm and compared with those reported for the Fc compound containing the 3-dicyanomethylidene-2,3-benzo[b]thiophen-1,1-dioxide group (1). The values of μβ·(2ω) are 160 and 280×10−48 esu for 2 and 3, respectively, whereas 1 displays a value of 140×10−48 esu [Inorg. Chim. Acta 242 (1996) 43]. The X-ray crystallographic study of 1 and 2 revealed significant distortions of the structure of the ferrocene moieties due to the contribution of a charge-separated η6-fulvene mesomeric form and important steric effects. The cyclic voltammetry data showed an anodic shift of the Fe(II)/Fe(III) oxidation potentials of 2 and 3 in comparison to those of ferrocenecarboxaldehyde (4) and 2-(ferrocenylmethylidene)-1,3-indandione (5), and an approximately additive effect of the substitution of one or two carbonyl oxygens in 5 by the C(CN)2 group.