New Hybrid Materials Made from Dipolar Fe(II) Arylacetylide Complexes Exhibiting Temperature-Dependent Second Harmonic Generation Properties

We show in this contribution that new hybrid materials which are active for second harmonic generation (SHG) can be obtained easily from dipolar organoiron(II) NLO-phores like (η²-dppe)(η⁵-C₅Me₅)Fe(C≡C-4-C₆H₄X) (1; X = NO₂ and 2; X = C(O)H; dppe = 1,2-(diphenylphosphino)ethane). These new materials are formed upon UV irradiation of dispersions of 1 or 2 in oligoether-acrylates (OEAs) in the presence of an electrostatic dc field. Monitoring the evolution of the second-order susceptibility of these mixtures during the photosolidification process reveals the appearance of a growing noncentrosymmetric arrangement of the organometallic chromophores. Using an optimized experimental protocol, we find solid samples can be isolated which present sizable second-order optical susceptibilities; an SHG value around 3 pm/V is obtained with the samples containing the nitro-functionalized complex 1, while less intense SHG responses were obtained with dispersions of 2. These results are briefly discussed in the light of DFT calculations on 1 and 2. We also show that, quite interestingly, the SHG of the resulting materials exhibits nonmonotonous temperature dependence with a maximum observed slightly above ambient temperature (310 K).