Ferrocenyl donor–organic acceptor complexes for second order nonlinear optics

Abstract

First hyperpolarizability ( β) of a set of donor–acceptor complexes derived by functionalizing two organic acceptors with a donor such as ferrocene or an aromatic ring through a –CN– linkage has been measured by hyper-Rayleigh scattering in solution. Spectral analysis of the second harmonic scattered light reveals that there is a significant two-photon fluorescence (TPF) contribution to the total signal in some compounds. In fact, the TPF contribution was as high as ∼25% in two compounds. The measured β values after correcting for TPF indicate that these molecules possess high second order nonlinearity, much larger than similar organic compounds or charge transfer complexes formed by ferrocenyl donors and organic acceptors. The dispersion free β values of these complexes have been calculated using two different methods depending on the nature of the complex. The conventional nonresonant two-state model which gives a good estimate of the intrinsic second order polarizability away from resonance, has been applied to compounds with no absorption around the second harmonic wavelength. Another model in which a damping parameter related to the inhomogeneous line width of the absorption band near the second harmonic frequency is used for obtaining reliable values of β 0, has been employed for the other compounds. In conjugation with anthraquinone as acceptor, ferrocene as a donor appears to be a better choice for quadratic nonlinear optics applications than conventional organic donors.