DNA binding and photophysical properties of platinum(II) polypyridines

Platinum(II) polypyridines typically have unique photophysical properties because of the occurrence of several charge transfer states. All platinum(II) polypyridines have a metal to ligand charge transfer (MLCT) state, but alteration of the terdentate ligand can introduce an intraligand charge transfer (ILCT) state. Modification of the ancillary ligand can also alter the photophysical properties and introduce another charge transfer state, a ligand to ligand charge transfer (LLCT). The work in Chapter 2 describes the binding mode of [Pt(dma-T)CN]+ to double stranded DNA. The DNA binding of [Pt(dma-T)CN] + is easy to monitor because of the impressive photophysics of the complex. [Pt(dma-T)CN]+ aggregates to DNA at high drug loading and intercalates at low loading. When the complex intercalates into DNA the complex is protected from solvent quenching. Chapter 3 describes how modification of the substituents in the 4' position of the terpyridine can change the orbital parentage of the lowest energy excited state. The [Pt(4'-NR 2-T)X]+ complexes emit from a mixed MLCT/ILCT state and the amount of ILCT character varies with the donor character of the substituent. In Chapter 4, the photophysics of orthometalated platinum(II) complexes are studied. The 6-phenyl-2,2'-bipyridine complexes have electronically active substituents on the terdentate ligand and/or the ancillary ligand. All of the complexes emit at room temperature in fluid solution, except the complexes with ethynyltrialkoxygallate co-ligands which undergo electronic reorganization. Surprisingly, the complexes with chloride ancillary ligands have the highest quantum efficiencies because the emitting state of the complexes with ethynylaryl co-ligands exhibits LLCT character which facilitates radiationless decay.