Strongly Coupled Cyclometalated Ruthenium Triarylamine Chromophores as Sensitizers for DSSCs

A series of anchor‐functionalized cyclometalated bis(tridentate) ruthenium(II) triarylamine hybrids [Ru(dbp‐X)(tctpy)] 2− [ 2 a ] 2− –[ 2 c ] 2− (H 3 tctpy=2,2′;6′,2′′‐terpyridine‐4,4′,4′′‐tricarboxylic acid; dpbH=1,3‐dipyridylbenzene; X=N(4‐C 6 H 4 OMe) 2 ([ 2 a ] 2− ), NPh 2 ([ 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(Me 3 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 I 3 − /I − couple and [Co(bpy) 3 ] 3+/2+ and [Co(ddpd) 2 ] 3+/2+ couples as [B(C 6 F 5 ) 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 I 3 − /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 .