Ligand-ligand triplet energy transfer in tetrametallic and monometallic ruthenium(II) terpyridyl Oligo(phenylene-vinylene) complexes and synthesis and photophysics of tolyl terpyridyl platinum(II) complexes

Photoinduced energy transfer plays an important role in natural processes such as photosynthesis. In the natural photosynthetic process, the pigment molecules namely chlorophyll absorb the light from the sun. Excitation energy then migrates from one chlorophyll molecule to another unidirectionally in an array and ultimately reaches the reaction center where charge separation occurs. In addition to its importance in natural phenomena, photoinduced energy transfer finds application in varied fields such as solar energy harvesting, sensors, information transfer and molecular electronics.Transition metal complexes are a useful class of "chromphores" and have been extensively used for light harvesting applications. The metal imine complexes (i.e. py(pyridine), bpy(2,2'-bipyridine), tpy(2,2':6',2"-terpyridine) of Ru(II), Os(II), Re(I) and Ir(III) have desirable properties that make them attractive for these applications. Compared to 2,2'-bipyridine-type complexes, 2,2':6',2"-terpyridine(tpy)-type complexes have been much less thoroughly examined, because the weak ligand field of tpy-type ligands results in a weak emissive and short-lived excited states of their complexes. However, tpy-type complexes have geometrical advantages, which are non-chiral and could lead to linear structures upon introduction of substituents at 4'-position of tpy. The goal of Chapter 2 has been to study ligand-ligand triplet energy transfer in tetrametallic Ru(II) terpyridyl phenylene vinylene complexes. Synergizing the properties of Oligo(1,4 phenylene-vinylene or OPV) and terpyridine symmetric and unsymmetric Ru(II) tetrametallic complexes have been synthesized. Excitation energy migration from an excited state localized on the tpvpvpt ligand to the tpvp(OR)vpt ligand in the heterometallic tetramer was monitored using transient absorption spectroscopy. The ligand tpvpvpt(terpyridyl phenyl vinyl phenyl vinyl phenyl terpyridine) is abbreviated in short as the 2 vinyl ligand(2V). Similarly tpvp(ORvpt) is abbreviated as 2vinyl alkoxy ligand (2V(OR).Chapter 3 also deals with ligand-ligand triplet energy transfer. In this case a bichromophoric complex with slightly different pi-pi* excited states has been synthesized. The complex in which ligand-ligand triplet energy was monitored is [(pyrtp)Ru(tpvp(OR)vpt)]2+(PF6) 2 (where pyr = pyrene tpy = 2,2':6',2"-terpyridine). In order to observe energy transfer from the pyrene triplet excited state to the alkoxy phenylene vinylene triplet, the complexes were made as PMMA(Polymethymethacrylate) matrices.Square-planar platinum (II) polypyridyl complexes represent an important class of compounds that possess a rich range of spectroscopic and photophysical properties. The aim was to synthesize simple and viable Pt(II) systems which would help us understand the structural and electronic factors that influence non-radiative relaxation. In this aspect we have synthesized a [(mpt)Pt(OH)] + complex. The spectroscopic and temperature-dependent luminescence lifetime studies of the hydroxo complex have been presented in Chapter 4.Chapter 5 deals with the synthesis, spectroscopic and temperature dependent luminescence lifetime studies of a series of tolyl terpyridyl platinum complexes (i.e) [mpt-Pt-L]x (Y) (L = Cl, MeCN, Py, DMASPy, PPh3 ) (x = 1 or 2) (Y = CF3SO3 or BF4) spanning the spectrochemical series. DMASPy is 4,[4-(Dimethyl amino)styryl pyridine)]. The ability to vary the L group affords the possibility of studying a series of related complexes.