Role played by the organometallic fragment on the first hyperpolarizability of iron-acetylide complexes: A TD-DFT study

The static first hyperpolarizabilities (beta) for a series of both substituted thiophene-acetylide ligands and the corresponding eta(5)-monocyclopentadienyliron(II) complexes were determined by density functional theory (DFT) calculations. The effect on the hyperpolarizabilities by various donor and acceptor substituents in the thiophene-acetylide ligands was studied. The nature and role of the electronic excitation contributions to the first hyperpolarizability, using time-dependent DFT (TD-DFT) calculations, are rationalized in terms of the two-level model. Our calculations show that the organometallic fragment can form a very effective push-pull system in combination with electron-withdrawing substituents in the thiophene-acetylide moiety, leading to enhanced static first hyperpolarizabilities. Also, an improvement of the magnitude of beta is expected if solvation effects are taken into account. (c) 2009 Elsevier B.V. All rights reserved.