Molecular second-order optical nonlinearities of metallocenes

Article abstract of DOI:10.1021/ja00019a020

The nonresonant quadratic molecular hyperpolarizabilities of several ferrocene and ruthenocene derivatives were studied by dc electric-field-induced second-harmonic generation (EFISH) experiments using fundamental radiation at 1.91 μm, Hyperpolarizabilities approaching that of 4-(dimethylamino)-4′-nitrostilbene (DANS) were observed, indicating that the ferrocene moiety can act as an effective donor. It was found that the dipole projections of the β tensors of ferrocene complexes are comparable to those of methoxyphenyl systems with similar acceptors. Thus, (E)-ferrocenyl-4-(4-nitrophenyl)ethylene (5) has a β value of 31 × 10^-30 esu whereas 4-methoxy-4′-nitrostilbene has a value for β of 29 × 10^-30 esu. Replacement of the iron atom with ruthenium, which has a higher ionization potential, leads to a reduction in β relative to 5. Replacement of a cyclopentadienyl ring with a pentamethylcyclopentadienyl ring leads to increased nonlinearity.