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

Abstract

η5-Monocyclopentadienyliron(II)/ruthenium(II) complexes of the general formula [M(η5-C5H5)(PP)(L1)][PF6] {M = Fe, PP = dppe; M = Ru, PP = dppe or 2PPh3; L1 = 5-[3-(thiophen-2-yl)- benzo[c]thiophenyl]thiophene-2-carbonitrile} have been synthesized and studied to evaluate their molecular quadratic hyperpolarizabilities. The compounds were fully characterized by NMR, FTIR and UV/Vis spectroscopy and their Introduction The exploitation of organometallic chemistry for the synthesis of compounds with non-linear optical (NLO) properties has been mainly motivated by their use in optical devices.[ 1] During the last two decades, significant work has been published outlining the most important progress in the field.[2–11] According to the overall results, the general understanding is that second-order non-linearities are strongly related to asymmetric push–pull systems. In the case of organometallic compounds, the metal centre can be bound to a highly polarizable conjugated backbone, thereby acting as an electron-releasing or -withdrawing group. This type of structural feature leads to large quadratic hyperpolarizabilities arising from intense low-energy metal-to-li- [a]