title: Syntheses and quadratic optical nonlinearities of ruthenium(II) complexes with ethynyl-connected N-methylpyridinium electron acceptors.
abstract: We have prepared a number of new dipolar complexes containing ethynyl or buta-1,3-diynyl units linking electron-rich {Ru(II)(NH3)5}2+, trans-{Ru(II)(NH3)4L}+ (L = pyridine or N-methylimidazole), or trans-{Ru(II)Cl(pdma)2}+ [pdma = 1,2-phenylenebis(dimethylarsine)] centers to pyridinium electron acceptors. In acetonitrile solutions at 295 K, the new complexes display unusual blue-shifting of their metal-to-ligand charge-transfer (MLCT) bands as the conjugation is extended, in a fashion similar to that of the corresponding ethenyl systems. Hyper-Rayleigh scattering (HRS) and Stark spectroscopic measurements provide direct and indirect estimates of static first hyperpolarizabilities beta0, and both the linear and nonlinear optical (NLO) properties are temperature- and medium-dependent. Thus, at 77 K in butyronitrile glasses, the MLCT bands display more normal red shifts upon conjugation extension. While the Stark-derived beta0 values generally increase as n (the number of ethynyl units) increases from 0 to 2, the HRS data show maximization at n = 1 for two of the ammine series but an increase upon moving from n = 1 to 2 for the pdma complexes. Comparisons with the analogous ethenyl chromophores show that the latter generally display larger beta0 values, whether determined via HRS or Stark data, and the inferiority of the ethynyl systems in terms of NLO response is more pronounced when n = 2. This differing behavior is attributable primarily to larger increases in the transition dipole moment mu12 (and, hence, donor-acceptor pi-electronic coupling) on elongation in the ethenyl chromophores.
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@man.ac.uk
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Coe
authors.forename: Josephine L
authors.initials: JL
authors.lastname: Harries
authors.forename: Madeleine
authors.initials: M
authors.lastname: Helliwell
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Brunschwig
authors.forename: James A
authors.initials: JA
authors.lastname: Harris
authors.forename: Inge
authors.initials: I
authors.lastname: Asselberghs
authors.forename: Sheng-Ting
authors.initials: ST
authors.lastname: Hung
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.forename: Peter N
authors.initials: PN
authors.lastname: Horton
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hursthouse