Proceedings Article | 13 October 1997
Juergen Heck, Hugo Brussard, Sven Dabek, Timo Meyer-Friedrichsen, Hans Wong
KEYWORDS: Nonlinear optics, Chromophores, Absorption, Hyper Rayleigh scattering, Resonance enhancement, Chemical species, Ruthenium, X-rays, Bromine, Information operations
Mono- and dinuclear sesquifulvalene-type complexes [{LnM(l5C5H4)}Z{17C7H6)MLtn}mXm+i (m =0, 1 ; X = BF4, PF6) have been synthesized, particularly with regards to their nonlinear optical properties. Z =-: LM = CpFe, M'L' = -, la; LM = CpFe; M'L' = Cr(CO)3, ib; LM = CpFe, ML',, = RuCp, ic; LM = CpFe, L'M' = RUCP*, id; LM = CpRu; M'L' = -, le; LM =CpRu, M'L' RuCp, if, LM = CpRu, M'L' = RuCp*, ig - Z = C2: LM = CpFe, M'L' = Cr(CO)3, 2 - Z = C2H2:LM = CpFe, ML' = -, 3a; LM = CpFe, M'L' = Cr(CO)3, 3b; LM = CpFe, L'M' = RuCp, 3c; LM = Cp*Fe, M'L' = Cr(CO)3, 3d; LM = (Ph4C4)Co, M'L' = - 5; Z = thiophene-1,5-diyl (C4H2S): LM = CpFe, M'L' = -, 4a; LM = CpFe, M'L' = RuCp) (Cp = C5H5, Cp* C5Me5, Ph = C6H5). The ferrocenyl containing complexes reveal UV/vis spectra, showing long wave absorption bands beyond 550 nm which are assigned to a charge transfer (CT) transition between the cyclo-C5 and cyclo-C-, moieties. The corresponding transitions for the ruthenocenyl compounds if and ig are found below 500 nm. The
CT transitions exhibit pronounced negative solvatochromism. Cyclic voltammetry studies and structural data of some of these compounds confirm the strong electronic coupling between the cyclo-C5 and the cyclo-C7 moieties. Hyper Rayleigh scattering (HRS) investigations of these mono- and dinuclear sesquifulvalene derivaties to determine the first hyperpolarizability 13 show several different important features: i) the measured 13 values of compounds with an additional
spacer Z are the highest ever obtained for sandwich-type NLO chromophores; ii) the B values of the dinuclear sequifulvalene complexes surpass the 13 values of the mononuclear derivatives markedly; iii) the exchange of a monocationic electron accepting group (Cr(CO)3), with a dicationic one (RuCp) enhances 13 considerably, iv) the use of the (cyclobutadiene)(cyclopentadienyl)Co unit reveals a surprisingly large B value although this compound is mononuclear. The large experimental 13 values are in part assigned to resonance enhancement.
