Abstract
In our continued efforts in the synthesis of ruthenium(II) polypyridine complexes as potential dyes for use in varied applications, such as the dye-sensitized solar cells (DSSCs), this work particularly describes the synthesis, absorption spectrum, redox behavior and luminescence properties of a new homoleptic ruthenium(II) complex bearing a simple trans-2-methyl-2-butenoic acid functionality as the anchoring ligand on terpyridine moiety. The functionalized terpyridine ligand: 4′-(trans-2-methyl-2-butenoic acid)-terpyridyl (L1) was synthesized by aryl bromide substitution on terpyridine in a basic reaction condition under palladium carbide catalysis. In particular, the photophysical and redox properties of the complex formulated as: bis-4′-(trans-2-methyl-2-butenoic acid)-terpyridyl ruthenium(II) bis-hexafluorophosphate [Ru(L1)2(PF6)2] are significantly better compared to those of [Ru(tpy)2]2+ and compare well with those of the best emitters of Ru(II) polypyridine family containing tridentate ligands. Reasons for the improved photophysical and redox properties of the complex may be attributed partly to the presence of a substituted α,β-unsaturated carboxylic acid moiety leading to increase in the length of π-conjugation bond thereby enhancing the MLCT-MC (Metal-to-ligand-charge transfer-metal centred) energy gap, and to the reduced difference between the minima of the excited and ground states potential energy surfaces.
Highlights
The search for new energy systems based on renewable sources which require less energy consumption and are more environmentally friendly draws more and more attention
In comparison to other synthesized ruthenium(II) bipyridyl and phenanthrolyl complexes earlier published [26,27,28], this paper reports most essentially an improved molar extinction coefficient, luminescence and redox properties of a new homoleptic bis-4’-(trans-2-methyl-2-butenoic acid)-terpyridyl ruthenium(II)
The reaction of 4’-bromoterpyridine and trans-2-Methyl-2-butenoic acid proceeded under a catalyzed palladium cross-coupling reaction in a basic medium and using high temperature afforded the desired coupling product as 4’-(trans-2-Methyl-2-butenoic acid)-terpyridine (L1) and the corresponding homoleptic complex [Ru(L1)2(PF6)2] resulted from its reaction with [RuCl2(dmso)4]
Summary
The search for new energy systems based on renewable sources which require less energy consumption and are more environmentally friendly draws more and more attention. The purpose of incorporating an α,β-unsaturated carboxylate group in the ligand is three-fold: (i) to increase the molar extinction coefficient of the complex through π-bond elongation; (ii) to facilitate the grafting of the dye on the semiconductor surface; and (iii) to ensure intimate electronic coupling between its excited-state wave function and the conduction band manifold of the semiconductor. It is well-known that substitution of carboxy groups at the.
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