Strongly Coupled Cyclometalated Ruthenium Triarylamine Chromophores as Sensitizers for DSSCs

Abstract

A series of anchor-functionalized cyclometalated bis(tridentate) ruthenium(II) triarylamine hybrids [Ru(dbp-X)(tctpy)](2-) [2 a](2-) -[2 c](2-) (H3 tctpy=2,2';6',2''-terpyridine-4,4',4''-tricarboxylic acid; dpbH=1,3-dipyridylbenzene; X=N(4-C6 H4 OMe)2 ([2 a](2-) ), NPh2 ([2 b](2-) ), N-carbazolyl [2 c](2-) ) was synthesized and characterized. All complexes show broad absorption bands in the range 300-700 nm with a maximum at about 545 nm. Methyl esters [Ru(Me3 tctpy)(dpb-X)](+) [1 a](+) -[1 c](+) are oxidized to the strongly coupled mixed-valent species [1 a](2+) -[1 c](2+) and the Ru(III) (aminium) complexes [1 a](3+) -[1 c](3+) at comparably low oxidation potentials. Theoretical calculations suggest an increasing spin delocalization between the metal center and the triarylamine unit in the order [1 a](2+) <[1 b](2+) <[1 c](2+) . Solar cells were prepared with the saponified complexes [2 a](2-) -[2 c](2-) and the reference dye N719 as sensitizers using the I3 (-) /I(-) couple and [Co(bpy)3 ](3+/2+) and [Co(ddpd)2 ](3+/2+) couples as [B(C6 F5 )4 ](-) salts as electrolytes (bpy=2,2'-bipyridine; ddpd=N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridine-2,6-diamine). Cells with [2 c](2-) and I3 (-) /I(-) electrolyte perform similarly to cells with N719. In the presence of cobalt electrolytes, all efficiencies are reduced, yet under these conditions [2 c](2-) outperforms N719.

Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment

“…107,109,118,119,137,151 Van Koten 137 and we 118,119 determined extremely low quantum yields in the range of 10 −5 for complexes of type [Ru(dpb-R 1 )(tpy-R 2 )] + . In contrast to the tris-(bidentate) series, however, no excited state lifetimes were reported so far ( Table 2).…”

“…16,17,19,[107][108][109] Additionally, cyclometalated bridging ligands enhance the electronic coupling between the redox centers in mixed-valent Ru/Ru complexes [110][111][112] and Ru/organic hybrid structures. [113][114][115][116] Despite the large variety of cyclometalated polypyridine ruthenium complexes synthesized up-to-date, however, no phosphorescence comparable to [Ru(bpy) 3 ] 2+ has yet been achieved.…”

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

“…The slow electron transfer kinetics of the reduction of [Co(ddpd) 2 ] 3+ can be beneficial for applications in dye-sensitized solar cells, retarding the undesired back-electron transfer (recombination) at the TiO 2 electrode [102]. However, dye-regeneration by [Co(ddpd) 2 ] 2+ is also slow [103]. Compared to the standard iodide/triiodide electrolyte, the overall performance of outer sphere cobalt(III/II) electrolytes in dye-sensitized solar cells depends on the dye and the electrode surface treatment among other factors [102,103,109,110].…”

Ruthenium Complexes as Sensitizers in Dye-Sensitized Solar Cells

“…Depending on the substituents on both, cyclometalating and polypyridine, ligands one may choose from the above-mentioned procedures. To synthesize cyclometalated Ru complexes of [Ru(tpy)(dpb)] + type (where dpbH = 1,3bis(pyridine-2-yl)benzene) with two tridentate ligands, one may start from Ru(tpy)Cl3 and abstract halogens with soluble silver salts, i.e., AgPF6 or AgBF4, in acetone, and then, without specific purification, react the obtained acetone ligated complex with a cyclometalating ligand as shown in Scheme 3 [94,96,[100][101][102][103][104]. Direct reaction of Ru(tpy)Cl3 with cyclometalating ligand in the presence of base/reducing agent was also shown to provide cyclometalation [95,[105][106][107].…”