Search

2-(1H-1,2,3-Triazol-4-yl)pyridines (trzpy), which can be regarded as analogues to 2,2'-bipyridines, were attached to the 2- and 7-position of 9,9-dioctyl-9H-fluorene providing one monotopic and two ditopic ligands. The bidentate N-heterocycles were synthesized by the copper(I)-catalyzed azide-alkyne 1,3-cycloaddition. Moreover, the palladium(0)-catalyzed Sonogashira coupling allowed the introduction of an electron-withdrawing phenylacetylene moiety at 5-position of the pyridine unit. The emission maximum of the ligands could be varied over a range of 100 nm with extinction coefficients up to 95 000 M-1·cm-1. Even though the monotopic system revealed a similar absorption behavior compared to its ditopic counterpart, a remarkable fluorescence quantum yield deviation of one order of magnitude was observed (φ = 0.66 for the unsubstituted ditopic and φ = 0.07 for the monotopic ligand). All trzpy systems were coordinated to ruthenium(II) ions in high yields (>90%) using the bis(4,4'-dimethyl-2,2'-bipyridine)ruthenium(II) precursor. Though 2-(1,2,3-triazol-4-yl)pyridine ligands are known to be potential quenchers for ruthenium(II) ions, all ruthenium complexes revealed room temperature phosphorescence, whereby emission lifetimes proved to be relatively short (<10 ns). Photophysical and electrochemical measurements indicated no electronic interaction of the two ruthenium centers. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study of the Förster resonance energy transfer (FRET) efficiency between thiazole dyes and a ruthenium–polypyridine complex is presented. While ruthenium–polypyridines are conventionally used in artificial light harvesting systems as primary electron donors, their application suffers from rather low extinction coefficients in the visible spectral range and an absorption gap between the ππ⁎ transitions of the ligands and the MLCT transitions. In this paper it is shown how thiazoles might help to circumvent theses issues. The absorption and emission spectra of the thiazole can be synthetically adjusted to fall into the absorption gap of the Ru dye and to efficiently overlap with the 1MLCT absorption of the complex, respectively. Thereby, the thiazoles might serve as antenna structures to funnel energy to the Ru-polypyridine unit, which finally can act as a photoactivated primary electron donor. Systematic investigations of the Förster radii of representative thiazole Ru-polypyridine dye pairs corroborate this potential quantitatively. [Copyright &y& Elsevier]