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With 2?chlorotrityl chloride resin; In ethanol; for 24h;Product distribution / selectivity; |
EXAMPLE 1 Freshly prepared titanium dioxide (TiO2) was coated onto a glass plate in the normal fashion (Argazzi et al., 1994). The plate was then dipped into a 3×10-4 M solution of 4,4'-dicarboxy-2,2'-biquinoline in ethanol for a period of 24 hours, washed thoroughly with ethanol, then air dried at room temperature. The presence of the anchored ligand was verified by IR comparison of TiO2 containing the adsorbed ligand with the pure ligand. The adsorption was quantified by desorbing the ligand into 0.1 M KOH (1:1 EtOH/H2O) and measuring the UV band at 260 nm. The loading was measured at 6.3×10-8 mol/cm2, which compared reasonably well with traditional dye-sensitized TiO2.The sensitizer complex was then synthesized in a stepwise fashion from the anchored dicarboxylate ligand. First, the plate was dipped in a 10-3 M acetonitrile solution of [Cu(CH3CN)4](PF6) for three hours, washed with acetonitrile and air-dried. The plate was then dipped into a 10-3 M dichloromethane solution of one of five bidentate secondary ligands: (1) 1,10-phenanthroline (?phen?); (2) 4,7-diphenyl-1,10-phenanthroline (?bap?); (3) 2,9-dimethyl-2,2'-bipyridine (?mbp?); (4) 2,9-dimethyl-1,10-phenanthroline (?mph?); and (5) 2,2'-biquinoline (?biq?). The structures of these secondary ligands are illustrated in Examples 2-8 below. The plate was then washed with solvent and air-dried.Formation of the sensitizer complex in the TiO2 matrix was evidenced by a color change of the glass plate. The characteristic long wavelength MLCT (metal-to-ligand charge transfer) absorption was observed spectrophotometrically. Both the intensities and the energies of the absorption bands were consistent with expectations based on the structures of secondary ligands 1-5. The complexes involving 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline exhibited the weakest bands, because these ligands lack ortho substituents which are well known to stabilize Cu(I) systems. The complexes involving 2,9-dimethyl-1,10-phenanthroline and 2,9-dimethyl-2,2'-bipyridine possess stabilizing ortho-methyl substituents and showed very similar, more intense absorptions. Finally, the complex with 2,2'-biquinoline was also stabilized towards oxidation and appeared at the lowest energy due to the increased electronegativity of the ligand.Evidence demonstrated that the sensitizer was not just being formed on the surface of the TiO2. When a 2-fold thicker coating of the titanium dioxide semiconductor material was applied to the glass plate, the intensity of the sensitizer absorption increased accordingly.Stability to oxygen is also a function of the secondary ligand structures. The absorbances associated with the structures incorporating secondary ligands 1 and 2 faded within a few hours after exposure to air, but were more stable under an Argon atmosphere. The other complexes, involving ortho-substituted ligands, were stable to air. |
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With 2?chlorotrityl chloride resin; In ethanol; dimethyl sulfoxide; for 24h;Product distribution / selectivity; |
EXAMPLE 2 TiO2-bqda-Cu(I)-biqA glass plate coated with a TiO2 film was dipped into a saturated solution of 4,4'-dicarboxy-2,2'-biquinoline (?bqda?) in DMSO/ethanol (v/v 1:20) for a period of 24 hours, washed thoroughly with ethanol, and then air dried at room temperature. The structure for bqda is shown below: The copper(I) complex was then synthesized in a stepwise fashion from the anchored dicarboxylate ligand. First, the plate was dipped into a 10-3 M acetonitrile solution of [Cu(CH3CN)4](PF6) for 12 hours, rinsed with acetonitrile and air dried. The plate was then dipped into a 10-3 M dichloromethane solution of a secondary ligand, 2,2'-biquinoline (?biq?) for 3 hours. The structure of the secondary ligand biq is shown below: The plate was then washed with dichloromethane and air dried at room temperature. The structure of the synthesized photosensitizer (Compound 1) is shown below. Formation of the heteroleptic copper (I) complex ([Cu(bqda)(biq)]+) on the TiO2 film was evidenced by a color change (from light red to violet red) of the glass plate and the characteristic long wavelength MLCT (metal-to-ligand charge transfer) absorption at 545 nm, shown in FIG. 4, which was observed spectrophotometrically. |