ABSTRACT
A series of cyclometalated complexes of ruthenium (II) with four different substituents in the aryl fragment of benzimidazole was synthesized in order to study the effect of substituent donation on the electronic structure of the substances. The resulting complexes were studied using X-ray diffraction, NMR spectroscopy, MALDI mass spectrometry, electron absorption spectroscopy, luminescence spectroscopy, and cyclic voltammetry as well as DFT/TDDFT was also used to interpret the results. All the complexes have intense absorption in the range of up to 700 nm, the triplet nature of the excited state was confirmed by measurement of luminescence decay. With an increase in substituent donation, a red shift of the absorption and emission bands occurs, and the lifetime of the excited state and the redox potential of the complex decrease. The combination of these properties shows that the complexes are excellent dyes and can be used as photosensitizers.
ABSTRACT
Cyclometalated Ru(ii) complexes with 2-arylbenzimidazole antenna ligands bearing electron-donor/withdrawing substituents and anchoring 4,4'-dimethoxycarbonyl-2,2'-bipyridine have been prepared and their structure, optical and electrochemical properties have been studied. The complexes possess enhanced light-harvesting characteristics compared to those of the standard N719 dye and absorb light up to 750 nm. In addition, they demonstrate reversible redox behavior with Ru3+/Ru2+ potentials being finely tuned by the change of the electron-donating ability of cyclometalated ligands. After a mild hydrolysis of dimethoxycarbonyl groups the excellent optical properties of the complexes remain unchanged and they show good efficiency when tested in dye-sensitized solar cells.
