Compromise between conjugation length and charge-transfer in nonlinear optical η5-monocyclopentadienyliron(II) complexes with substituted oligo-thiophene nitrile ligands: synthesis, electrochemical studies and first hyperpolarizabilities

• Autor(a) principal: Mendes, Paulo J.
• Data de Publicação: 2007
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10174/5328
• topic: Iron complexes; Thiophene nitrile ligands; Cyclic voltammetry; Nonlinear optics; Quadratic hyperpolarizabilities; Molecular first hyperpolarizabilities

A systematic series of η5-monocyclopentadienyliron(II) complexes with substituted oligo-thiophene nitrile ligands of general formula [FeCp(P_P)(NC{SC4H2}nNO2)][PF6] (P_P=dppe, (+)-diop; n=1-3) has been synthesized and characterized. The electrochemical behaviour of the new compounds was explored by cyclic voltammetry. Quadratic hyperpolarizabilities () of the complexes with dppe coligands have been determined by hyper-Rayleigh scattering (HRS) measurements at two fundamental wavelengths of 1.064 and 1.550 m, to uncover the two-photon resonance effect and to estimate static  values. The obtained overall results are found to be better than for the related η5-monocyclopentadienyliron(II) complexes with p-benzonitrile derivatives. Although an increase of the resonant  at 1.064 m with increasing number of thiophene units in the conjugated ligand was found (up to 910 x 10-30 esu), the static values 0 remain practically unchanged, as shown by the 1.550 m measurements. Combined with the electrochemical and spectroscopic data (IR, NMR, UV-Vis), this remarkable evolution of  shows that the increase of conjugation length is balanced by a decrease in charge-transfer efficiency.