| Autor: |
Loftus LM; Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States., Li A; Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States., Fillman KL; Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States., Martin PD; Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States., Kodanko JJ; Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States., Turro C; Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States. |
| Abstrakt: |
Four Ru(II) complexes were prepared bearing two new tetradentate ligands, cyTPA and 1-isocyTPQA, which feature a piperidine ring that provides a structurally rigid backbone and facilitates the installation of other donors as the fourth chelating arm, while avoiding the formation of stereoisomers. The photophysical properties and photochemistry of [Ru(cyTPA)(CH 3 CN) 2 ] 2+ (1), [Ru(1-isocyTPQA)(CH 3 CN) 2 ] 2+ (2), [Ru(cyTPA)(py) 2 ] 2+ (3), and [Ru(1-isocyTPQA)(py) 2 ] 2+ (4) were compared. The quantum yield for the CH 3 CN/H 2 O ligand exchange of 2 was measured to be Φ 400 = 0.033(3), 5-fold greater than that of 1, Φ 400 = 0.0066(3). The quantum yields for the py/H 2 O ligand exchange of 3 and 4 were lower, 0.0012(1) and 0.0013(1), respectively. DFT and related calculations show the presence of a highly mixed 3 MLCT/ 3 ππ* excited state as the lowest triplet state in 2, whereas the lowest energy triplet states in 1, 3, and 4 were calculated to be 3 LF in nature. The mixed 3 MLCT/ 3 ππ* excited state places significant spin density on the quinoline moiety of the 1-isocyTPQA ligand positioned trans to the photolabile CH 3 CN ligand in 2, suggesting the presence of a trans-type influence in the excited state that enhances ligand exchange. Ultrafast spectroscopy was used to probe the excited states of 1-4, which confirmed that the mixed 3 MLCT/ 3 ππ* excited state in 2 promotes ligand dissociation, representing a new manner to effect photoinduced ligand exchange. The findings from this work can be used to design improved complexes for applications that require efficient ligand dissociation, as well as for those that require minimal deactivation of the 3 MLCT state through low-lying metal-centered states. |
