A heteroleptic iron(II) complex [Fe(dcpp)(ddpd)](2+) with a strongly electron-withdrawing ligand (dcpp, 2,6-bis(2-carboxypyridyl)pyridine) and a strongly electron-donating tridentate tripyridine ligand (ddpd, N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) is reported. Both ligands form six-membered chelate rings with the iron center, inducing a strong ligand field. This results in a high-energy, high-spin state ((5) T2 , (t2g )(4) (eg *)(2) ) and a low-spin ground state ((1) A1 , (t2g )(6) (eg *)(0) ). The intermediate triplet spin state ((3) T1 , (t2g )(5) (eg *)(1) ) is suggested to be between these states on the basis of the rapid dynamics after photoexcitation. The low-energy π(*) orbitals of dcpp allow low-energy MLCT absorption plus additional low-energy LL'CT absorptions from ddpd to dcpp. The directional charge-transfer character is probed by electrochemical and optical analyses, Mößbauer spectroscopy, and EPR spectroscopy of the adjacent redox states [Fe(dcpp)(ddpd)](3+) and [Fe(dcpp)(ddpd)](+) , augmented by density functional calculations. The combined effect of push-pull substitution and the strong ligand field paves the way for long-lived charge-transfer states in iron(II) complexes.

Reversing the metal-to-ligand charge transfer ( 3 MLCT)/metal-centered ( 3 MC) excited state order in iron(II) complexes is ac hallengingo bjective, yet would finally result in long-sought luminescent transition-metal complexes with an earth-abundant central ion. One approacht oa chieve this goal is based on low-energy charge-transfer absorptions in combination with as trong ligand field. Coordinating electron-rich and electron-poor tridentate oligopyridine ligands with large bite angles at iron(II) enables both low-energy MLCT absorption bands around 590 nm and as trong ligand field. Variations of the electron-rich ligand by introducing longer alkyl substituents destabilizes the iron(II) complex towards ligand substitution reactions while hardly affecting the optical properties. On the other hand, N-deprotonation of the ligand backbone is feasible andr eversible, yielding deep-green complexes with charge-transfer bands extending into the near-IRr egion.T ime-dependent density functional theory calculations assign these absorption bands to transitions with dipole-allowed ligand-to-ligand charget ransfer character.T his unique geometric and electronic situation establishes af urtherr egulating screw to increase the energy gap betweenp otentially emitting charge-transfer states and the non-radiativeligand field states of iron(II) dyes.

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.

A molecular triad composed of a triarylamine donor, a triarylborane acceptor, and a photoisomerizable dithienylethene bridge has been synthesized and explored by cyclic voltammetry, UV-vis, and luminescence spectroscopy. The effects of irradiation with UV light and fluoride addition on the electrochemical and optical spectroscopic properties of the donor-bridge-acceptor molecule were investigated. Photoisomerization of the dithienylethene bridge affects the triarylboron reduction potential, but not the triarylamine oxidation potential. UV-vis experiments reveal that the association constant for fluoride binding at the triarylborane site is independent of the isomerization state of the bridge. Irradiation of a THF solution of our donor-bridge-acceptor molecule with UV light, followed by F(-) addition, leads to a different color of the sample than UV irradiation alone or F(-) addition alone.

Dye‐sensitized solar cells equipped with cationic and neutral RuII‐based sensitizers [Ru(ddpd){tpy(COOH)3}]2+ [12+; ddpd = N,N′‐dimethyl‐N,N′‐di(pyridin‐2‐yl)pyridin‐2,6‐diamine, tpy(COOH)3 = 2,2″6′,2″‐terpyridine‐4,4′,4″‐tricarboxylic acid] and [Ru(ddpd){tpy(COOH)(COO)2}] (2) with and without the coadsorbent chenodeoxycholic acid were constructed with I3–/I– or the CoIII/II‐based redox mediators [Co(bpy)3]3+/2+ (33+/2+; bpy = 2,2′‐bipyridine) and [Co(ddpd)2]3+/2+ (43+/2+) in the presence of LiClO4 and 4‐tert‐butylpyridine. The best photovoltaic performance was achieved by using the 43+/2+ shuttle and the neutral sensitizer 2 without coadsorbent. The higher short‐circuit photocurrent density and higher electron recombination lifetimes obtained with this combination suggest slow electron recombination kinetics at the TiO2 surface with the CoIII complex 43+. The slow electron transfer to 43+ is tentatively ascribed to the high‐lying π* orbitals of the electron‐rich ddpd ligands, which result in a weak electronic coupling. This contrasts with the faster recombination with 33+, which features the low‐energy π* orbitals of the bpy ligands.