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Zinc and ruthenium quinone diimine complexes: synthesis and photophysical properties
| Title: | Zinc and ruthenium quinone diimine complexes: synthesis and photophysical properties |
| Author: | Dollberg, Christopher L. |
| Description: | Previously, rhodium complexes containing quinone diimine complexes have been shown to possess an excited state, bind to DNA, and photochemically cleave the duplex DNA strand. Much of this work has utilized the octahedral complex Rh(phi)2(phen)3+, where the phi ligand was intercalated in between the DNA base pairs. The method of photocleavage was not known, as the role of the metal in the excited state was not known. In order to identify ligand centered properties, analogous quinone diimine complexes must be produced that have no possible metal centered transitions. In the present work, Zn2+ (d10) was used to synthesize a series of tetrahedral complexes containing the quinone diimine ligands phi, bqdi, and nqdi. One such complex, [Zn(bqdi)(H2O)2](BF4)2, has good aqueous solubility, room temperature emission, and a pKa = 5.21. The electronic absorption spectrum is pH-dependent as shown by a shift of a visible region transition from λmax = 450 nm (pH = 3) to λmax = 418 nm (pH = 8), which was assigned as an Intra-Ligand-Charge-Transfer (ILCT). The deprotonated complex has a strong emission (λmax = 576 nm) as indicated by a quantum yield (Φ = 0.026) similar to Ru(bpy)32+. Since the complex is considerably less emissive in the protonated form and shows reversibility from pH = 2 to 11, it could be utilized as pH sensitive probe that functions as a light switch. [Zn(bqdi)(H2O)2](BF4)2 possesses a complicated equilibria between two different protonation forms excited states, as two lifetimes in the range of 1-6 ns were observed simultaneously regardless of efforts to isolate. Due to stability under biological conditions, [Zn(bqdi)(H2O)2](BF4)2 is suitable for DNA binding and photocleavage studies, which are currently in process. Further studies have been performed with other zinc complexes of bqdi and nqdi as well as ruthenium quinone diimine complexes to ascertain the nature of the ligand centered transitions. Previously, rhodium complexes containing quinone diimine complexes have been shown to possess an excited state, bind to DNA, and photochemically cleave the duplex DNA strand. Much of this work has utilized the octahedral complex Rh(phi)2(phen)3+, where the phi ligand was intercalated in between the DNA base pairs. The method of photocleavage was not known, as the role of the metal in the excited state was not known. In order to identify ligand centered properties, analogous quinone diimine complexes must be produced that have no possible metal centered transitions. In the present work, Zn2+ (d10) was used to synthesize a series of tetrahedral complexes containing the quinone diimine ligands phi, bqdi, and nqdi. One such complex, [Zn(bqdi)(H2O)2](BF4)2, has good aqueous solubility, room temperature emission, and a pKa = 5.21. The electronic absorption spectrum is pH-dependent as shown by a shift of a visible region transition from λmax = 450 nm (pH = 3) to λmax = 418 nm (pH = 8), which was assigned as an Intra-Ligand-Charge-Transfer (ILCT). The deprotonated complex has a strong emission (λmax = 576 nm) as indicated by a quantum yield (Φ = 0.026) similar to Ru(bpy)32+. Since the complex is considerably less emissive in the protonated form and shows reversibility from pH = 2 to 11, it could be utilized as pH sensitive probe that functions as a light switch. [Zn(bqdi)(H2O)2](BF4)2 possesses a complicated equilibria between two different protonation forms excited states, as two lifetimes in the range of 1-6 ns were observed simultaneously regardless of efforts to isolate. Due to stability under biological conditions, [Zn(bqdi)(H2O)2](BF4)2 is suitable for DNA binding and photocleavage studies, which are currently in process. Further studies have been performed with other zinc complexes of bqdi and nqdi as well as ruthenium quinone diimine complexes to ascertain the nature of the ligand centered transitions. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1071171484
http://hdl.handle.net/2374.OX/8597 |
| Date: | 2004 |
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