Hyper-Rayleigh scattering study of η5-monocyclopentadienyl–metal complexes for second order non-linear optical materials

Synthesis, Characterisation and Molecular Hyperpolarisabilities of Pseudo‐Octahedral Hydrido(nitrile)iron(II) Complexes for Nonlinear Optics: X‐ray Structure of [Fe(H)(dppe)2(4‐NCC6H4NO2)][PF6]·CH2Cl2

“…This weakening of the NC bond is consistent with a π back-donation interaction d π (Fe)-π*(NC), which makes the metal group a more effective donor. This shift is found to be much higher in the present complexes than in the cyclopentadienyl compounds, [10] where shifts of up to 35 cm -1 were obtained. The π back-donation is enhanced by the interaction between the electron-donating metal moiety and the electron-accepting nitro group through the conjugated chain, as desired for a large first hyperpolarisability.…”

“…The outer regions of this range was used to correct the HRS signal for multi-photon fluorescence, as described before. [4,10] A large photoluminescence background was only observed for one of the free ligands (L3, see Table 1), for which the luminescence signal, integrated over the central region of 6 nm, was about equal to the actual HRS signal. HRS measurements were performed in a rectangular fused silica cell containing a dilute solution of the compound in chloroform.…”

“…We have previously reported hyper-Rayleigh scattering (HRS) results for such a systematically varied series of ionic organometallic complexes, consisting of a transition metal centre coordinated by an η 5 -monocyclopentadienyl ring, a bidentate phosphane ligand and a conjugated nitrile ligand. [10][11][12] By comparing complexes with electron-donor and -acceptor substituted ligands we found that the ruthenium and especially the iron fragments could be used as very efficient electrondonor groups.…”

Benzo[c]thiophene Chromophores Linked to Cationic Fe and Ru Derivatives for NLO Materials: Synthesis Characterization and Quadratic Hyperpolarizabilities

“…The existence of this interaction was found to play an important role in the secondorder NLO response of the η 5 -monocyclopentadienyliron, -ruthenium, -nickel and -cobalt complexes with para-substituted benzonitrile chromophores, with the high values found for the Ru II and Fe II complexes being attributed to π-back-donation. [18] The fact that the experimental quadratic hyperpolarizabilities for all the complexes are relatively similar is not surprising considering the spectroscopic data discussed above. In fact, for the low-energy band, which is the key to second-order non-linear optical properties, λ max is very similar for all the complexes and no significant solvatochromic effect was observed.…”

“…Among the organometallic compounds presenting this structural feature, our group and others have carried out systematic studies on η 5 -monocyclopentadienylmetal complexes with benzene or oligothiophene conjugated chains coordinated to the metal centres through nitrile or acetylide linkages. [8,[12][13][14][15][16][17][18] In particular, very efficient NLO responses were found when strong electron donors such as iron and ruthenium organometallic moieties were coupled with strong electron acceptors like NO 2 .…”