Synthesis and photophysics of platinum(II) terpyridyl complexes

Platinum(II) terpyridyl complexes are square-planar d 8 complexes. The coordination of platinum(II) ion features one terpyridyl ligand and the fourth coordination site with a donor coligand X. The complexes usually exhibit moderate metal-to-ligand charge-transfer (1MLCT) absorption and 3MLCT emission. In the current dissertation work, a series of mono- and di-nuclear platinum terpyridyl complexes are designed and synthesized. The photophysical properties including electronic absorption, photoluminescence, and triplet excited-state properties are systematically investigated to elucidate the structure-property relationships. The potential application of these complexes as pH sensors, nonlinear absorbing materials, and photosensitizers are demonstrated.;In chapter 2, the electron delocalization was observed for a series of 4'-(5"'-R-pyrimidyl)-2,2':6',2"-terpyridine platinum phenylacetylide complexes. They exhibit broad and moderate intense triplet excited-state absorption from 500-800 nm, and show moderate nonlinear transmittance at 532 nm for nanosecond laser pulse. In addition, these complexes can generate singlet oxygen in a reasonable quantum yield. In Chapter 3, the photophysical properties of platinum terpyridyl phenylacetylide complexes with -Cl, -CN,-N(CH3) 2 substituent at the 4'-position of the tepyridyl ligand were systematically investigated. The complex with -N(CH3)2 substituent displays a much higher emission quantum yield and long emission lifetime due to the admixture of 3ILCT (intraligand charge transfer) / 3pi,pi* characters in its emitting state. The result is confirmed by the TD-DFT calculation. In Chapter 4, the photophysical studies of a series platinum terpyridyl chloride complexes with nitrophenyl group as an acceptor reveal that the 1MLCT absorption and the 3MLCT emission of these complexes could be tuned by the conjugation length and the nature of the linker group between nitrophenyl group and the tepyridyl ligand. In Chapter 5, a new platinum terpyridyl complex with dimethylamino substituent on the phenylacetylide ligand and a hydroxylphenyl substituent on the terpyridyl ligand were synthesized. This complex displays drastic color change and emission intensity change in the presence of acids and bases due to the switch between the MLCT, LLCT, and ILCT excited states upon protonation and deprotonation. A series of dipolar terpyridyl ligands with diphenylamino groups as electron donor, terpyridyl group as electron acceptor, and fluorenyl group as pi bridging group, as well as their platinum chloride complexes were successively synthesized and discussed in Chapter 6. The solvent-dependent studies of the ligands suggest the large dipole moment change between the ground state and the excited state. These ligands exhibit moderate two-photon absorption in the near-IR region. All platinum complexes exhibit weak fluorescence from configurationally mixed 1ILCT, 1pi,pi*, and 1MLCT excited state.;In Chapter 7, ditopic terpyridine ligands and their platinum complexes with back-to-back structure were designed and synthesized. The lowest-energy absorption band of all complexes is assigned as the 1pi,pi*/1ILCT/1MLCT transition. The origin of the emission for the platinum complexes at room temperature is tentatively assigned to a mixture of five configurationally distinct excitations 3pi,pi* /1,3ILCT/1,3MLCT.