Stilbazole complexes, ligands

The only photoreaction which the 4-styrylpyridine (4-stilbazole) complexes [Ru(bipy)(cw-4-stilbazole)] + and [Ru(bipy)(/ ra 5-4-stilbazole)] + undergo is that of cis trans isomerization of the stilbazole ligands there is no significant photodissociation. The anion [Pt(NH3)4(NH2)(N02)] " photoisomerizes to [Pt(NH3)4(NHa)(ONO)]. The quantum yield has been determined for this process, but no kinetic results are available. ... 

Another approach to get new liquid crystals is the lateral fluorination of the stilbazole ligands,337 which is a common and highly effective tool to exert control over mesomorphism, crystal phase stability, and physical properties. Other modifications include the use of more alkoxy substituents and other alkyl sulfate anions.338-344 Ionic silver amino complexes also display liquid crystalline behavior at rather low temperatures they are of the form [Ag(NH2 -CJl +OJX (X = N03, n = 6,8,10,12,14 X = BF4, = 8,10,12,14).345... 

The EFISHG technique has also been applied to some pyridyl carbonyls of Rh1 or Ir1 by Bruce et al72,13 These complexes (e.g., (9) and (10)) contain stilbazole ligands bearing resolved 2-methylbutyloxy substituents, incorporated with the aim of encouraging noncentrosymmetric crystal packing structures. The observed 1.5- to 3-fold enhancements of (3 of the free stilbazole on complexation are attributable to the er-electron-withdrawing abilities of the metal centers.72,73... 

Metal perturbation of IL photochemistry appears to be less important in [Ru(bipy)2(h- n.s-4-stilbazole)2]2+ and [Ru(bipy)2(cw-4-stilbazole)2]2+. Both complexes undergo wavelength-dependent isomerization of the coordinated stilbazole ligands as the only important photoreaction."4 This wavelength dependence has beep attributed to the presence of two different types of reactive excited states, aRu-t stilbazole CT state which favors formation of the trans isomer and a higher energy IL state localized on stilbazole which decays with nearly equal probability to the two isomers. The latter pathway is qualitatively similar to the isomerization process that obtains upon direct photolysis of the free ligand. Thus coordination to Ru has not altered the characteristic photoreaction mode of the stilbazole molecule. 

Mean Linear Polarizabilities (a) and Polarizability Anisotrophies (Aa) for a Stilbazole Ligand and Its Iridium (I) Complex ... 

Electropolymerization of 4-Vinylpyridine Complexes. Investigations of Structural and Electronic Influences on Thin Film Formation. The recent discovery of the reductive polymerization of complexes containing vinylpyridyl ligands (lg), such as Ru -(bpy)2(vpy)22+ has led to the preparation of homogeneous thin layers of very stable electroactive polymers. This method has been extended to 4-vinyl-4 -methyl-2,2 -bipyridine (lg, 21a) and 4-vinyl-l,10-phenanthroline (21b) on both ruthenium and iron. In the following section we discuss our results on thin films derived from the polymerizable ligands BPE and the trans-4 -X-stilbazoles, (4 -X-stilb X - Cl, OMe, CN and H). 

The linear plot in Figure 7 of log( —j<—) (see Table 2, footnote g) and the Taft-Hammett (23) ap parameter for these complexes Ru(bpy)2(4 -X-stilb)2 + arises because the increasing ap parameter reflects the more anodic redox potential for the vinyl ligand, which results in a greater concentration of initiator, a more rapid polymerization reaction, and hence a greater amount of polymer deposition on the electrode surface. Such a correlation is indeed remarkable because it implies a greater surface coverage per unit time only if factors such as steric bulk, polymer conformation and rate of polymer precipitation remain relatively constant for the substituted trans-stilbazole series. 

We have pursued the study of polycatenar metallomesogens using poly(alkoxy) stilbazoles [177], and have recently imdertaken a systematic study of the complexes of series of these ligands with palladium(ll), platinum(II) and silveifl) ions. 

Of those investigated, the tetracatenar complexes of Pd and Pt with 3,4-disubstituted stilbazoles, 40, one complex 41 (M=Pd, n=14), and the hexacatenar complexes of Pd with 3,4,5- and 2,3,4-trisubstituted ligands (43 and 44, respectively) were mesomorphic. The two other series of complexes... 

Pyridines are known to form a variety of stable metal complexes and so elaborated pyridines are neutral targets for ligands in metallomesogens. Various substituted pyridines have been used in this context and the greatest amount of work has been carried out with the tran5-4-alkoxy-4 -stilbazoles (Figure 78, n-OPhVPy)7 The materials chemistry of these stilbazoles has been reviewed recently. ... 

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