Syntheses and Properties of Salts of Chromophores with Ferrocenyl Electron Donor Groups and Quaternary Nitrogen Acceptors
Coe, Benjamin J × Docherty, Rebecca J Foxon, Simon P Harper, Elizabeth C Helliwell, Madeleine Raftery, James Clays, Koen Franz, Edith Brunschwig, Bruce S #
Amer chemical soc
Organometallics vol:28 issue:24 pages:6880-6892
A series of five new dipolar cations hits been synthesized with ferrocenyl (Fc) electron donor groups connected to N-arylpyridinium, N-methylquinolinium, N-methylbenzothiazolium, or N-methylacridinium acceptors. Together with their known N-methylpyridinium analogue, these chromophores have been characterized as their PF6- salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Nine single-crystal X-ray structures have been determined, including two polymorphs of one salt obtained from it single crystallization experiment, and two of these are polar materials. A highly favorable degree of dipolar alignment for bulk NLO effects is observed in one case. Molecular quadratic nonlinear optical (NLO) responses have been determined by using femtosecond hyper-Rayleigh scattering (HRS) at 1300 rim and also via Stark (electroabsorption) spectroscopic studies oil the intense pi -> pi* intraligand and d -> pi* metal-to-ligand charge-transfer bands. A broad correlation between the electron acceptor strength and the HRS-derived first hyperpolarizabilities beta and the static first hyperpolarizabilities beta(0) estimated from the Stark data is evident. This is the first time that meaningful (albeit indirectly determined) beta(0) data have been reported for Fc compounds, allowing quantitative comparisons with the chromophore in the technologically important material (E)-4'-(dimethylamino)-N-methyl-4-stilbazolium (DAS) tosylate. The observed beta(0) values are in several cases similar to that of [DAS]PF6, and possibly even larger in one instance.