In order to investigate the structure−property relationship of nonlinear optical materials, a series of organometallic chromophores were synthesised utilising the [Fe 2 (η-C 5 H 5 ) 2 (CO) 2 (µ-CO)(µ-C−)] + electron-accepting moiety and the ferrocenyl group, Fc, as the electron donor. The π-linker between these two termini was systematically modified and the mutual electronic communication between them was determined using IR, NMR, and electronic absorption spectroscopy. An X-ray structure determination of [Fe 2 (η-C 5 H 5 ) 2 (CO) 2 (µ-CO)(µ-C−CH=CH−CH=C(Cl)−Fc)][BF 4 ] confirmed the strong electronic interaction between the donor and the acceptor with reduced π-bridge bond-length alternation. The nonlinear optical properties of these complexes were examined using the hyper Rayleigh scattering technique. The experimental first hyperpolarisabilities are some of the highest obtained for ferrocenyl chromophores and, significantly, no enhancement