| Sonogashira coupling reactions have been used for the synthesis of three functional systems: arylethynyl-substituted 9,10-anthraquinones, Os(II) bis(2,2 '-bipyridine) (3,8-diarylethynyl-1,10-phenanthroline) complexes and four star-shaped molecules incorporating the 4-benzoyl-N-alkylpyridinium cation.; The redox properties of 2-, 2,6- and 2,7-arylethynyl substituted 9,10-anthraquinones are almost insensitive to substitution, but their absorption maxima are linearly related to the Hammett constants. Importantly, all these compounds are photoluminescent both in solution and as solids with large Stokes shifts, which are attributed to large dipole moment differences between the ground and the excited state. Maximum Stokes shifts are attained by both electron donating and electron withdrawing groups. X-ray crystallographic analysis of 2,7-bisphenylethynyl-9,10-anthraquinone reveals (a) the monoclinic P21/n space group; and, (b) no indication for pi-overlap that would promote quenching, thus explaining emission from the solids. The emission of the reduced forms of these compounds is blue-shifted relative to the emission of the oxidized forms, and is attributed to internal transitions in the dihydro-9,10-anthraquinone core.; Os(II) complexes incorporating the 3,8-diarylethynyl-1,10-phenanthroline ligand were designed for pushing the metal-ligand charge transfer (MLCT) emission to the near infrared. Indeed, complexes with phenylethynyl and p-methoxyphenylethynyl substituted ligands emit at 815 nm and 795 nm, respectively.; The four star systems of this study were designed with their redox potentials varying along the branches, but remaining constant at fixed radii. Bulk electrolysis shows that at a semi-infinite time scale all redox centers are electrochemically accessible. Voltammetric analysis (cyclic voltammetry and differential pulse voltammetry) shows that only two of the three redox-active centers in the perimeter are electrochemically accessible during potential sweeps as slow as 20 mV s-1 and as fast as 10 V s-1.; Finally, it was shown that the Suzuki-Miyaura reaction comprises a viable alternative to the Sonogashira coupling reaction of bifunctional reagents, which, under the Sonogashira conditions, may lead to polymerization. (Abstract shortened by UMI.)... |
