Chelating Fluorene Dyes as Mono- and Ditopic 2-(1H-1,2,3-Triazol-4-yl)pyridine Ligands and Their Corresponding Ruthenium(II) Complexes

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.