Ligands photophysics

When the reaction of [AujCgFsjjtht)] is carried out with C6F4NCSPPh2 the complex [56] shovm in Figure 3.5 was obtained and its structure was determined by X-ray diffraction. The benzothiazole ligands are known to display photophysical properties vdth an improvement of the photostability and emission intensity in conjugated systems as well as in the complexes that contain them, and the presence of... 

Fernandez, E.J., Laguna, A., Lopez-de-Luzuriaga, J.M., Monge, M., Montiel, M., Olmos, M.E. and Rodriguez-Castillo, M. (2006) Synthesis, coordination to Au(I) and photophysical properties of a novel polyfiuorinated benzothiazolephosphine ligand. Dalton Transactions, (30), 3672-3677. 

To substitute the strongly bound axial CO ligand of the ruthenium or osmium center, it is necessary to employ more drastic conditions than simple stirring at room temperature. Imamura (11,20) used photolysis to synthesize porphyrin trimers on the basis of simultaneous coordination of two 4-pyridyl porphyrins to the same ruthenium porphyrin (12, Fig. 3). Some interesting photophysical behavior was observed for these systems. The trimers have an extra UV-Vis absorption band at about 450 nm which is ascribed to metal-ligand charge transfer (MLCT), a d7r(Ru(II))-7r (OEP) transition. This band shows a batho-chromic shift in more polar solvents, and decreased in intensity when... 

A typical ligand capable of generating a dendritic structure is 1,4,5,8,9,12-hexaazatriphenylene (HAT). Photophysical studies of trinuclear species based on HAT have been reported [14 a, 49]. Representative example of complexes of this type are 26, 27, and 28. For some of these complexes, the luminescence, originating from MLCT levels involving the central HAT ligand, was found to decay with multiexponential kinetics. Furthermore, the vibrational modes responsible for the nonradiative decay of the luminescent MLCT states are different in the polynuclear dendritic edifices with respect to the mononuclear [M(L)2(HAT)]2+ compounds [14a]. 

Other first-generation dendrimers built around multichelating ligands are the trinuclear complexes 29 - 38 [50-52] and several hexanuclear complexes (for representative examples, see 39 and 40) [53]. In all of these compounds, the photophysical properties are equivalent to those of their building blocks. In the mixed-metal complexes 31 and 34 [50b] the Ru(II)- and Os(II)-based chromo-phores are only weakly-coupled and a dual luminescence is observed. 

The adsorbed sensitizers in the excited state inject an electron into the conduction band of the semiconductor substrate, provided that the excited state oxidation potential is above that of the conduction band. The excitation of the sensitizer involves transfer of an electron from the metal t2g orbital to the 7r orbital of the ligand, and the photo-excited sensitizer can inject an electron from a singlet or a triplet electronically excited state, or from a vibrationally hot excited state. The electrochemical and photophysical properties of both the ground and the excited states of the dye play an important role in the CT dynamics at the semiconductor interface. 

Having thus illustrated the use of organic ligands as fluorescent sensors, we will now consider the applications of the photophysical properties of coordination compounds themselves. All the... 

The modification of the physical properties of some molecules as consequence of complexation with CDs is well known. Kongo et al.126 studied the TB-p-CD/porphyrine complex and observed a drastic change in the photochemical and photophysical properties of porphyrine. The conformational analysis by NMR revealed strong NOE interactions between the ligand and the internal part of the CD, in agreement with a deep insertion of the porphyrine analogue into the CD s cavity. The NOE data provided structural information to propose the 3D model of 1 2 inclusion complexes. 

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