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During the past decade, transition metal complexes have been widely used in functional
materials. Amongst, triplet emitting ruthenium(II) and iridium(III) complexes have immense
applications in OLED, sensing and bioimaging owing to their high luminescent efficiency and
tuneable excited and emission wavelength over the whole visible range. Particularly
cyclometalated units can influence the HOMO and LUMO energy levels and excited state
characters of the Ir(III) complexes and tune the photophysical properties like
photoluminescence, colour, lifetime, etc. Most of the phosphorescent Ir(III) complexes show
various charge transfer phenomena in the lowest triplet excited state (T1), such as metal to
ligand charge transfer (3MLCT), intraligand charge transfer (3
ILCT) and ligand to ligand
charge transfer (3LLCT) excited state characters. Recent reports on cyclometalated Ir(III)
complexes include an attempt to identify the nature of their lowest excited states because these
states are mainly responsible for the photophysical/chemical and photocatalytic properties. The
excited state properties of polypyridyl complexes of Ru(II) are often complicated by low-lying
triplet d-d or ligand field states. These states are formed by 3MLCT excitation to a metal
cantered (3MC) state. Once populated, 3MC became highly distorted and underwent rapid non-
radiative decay. Several research works have already demonstrated the potential use of
heteroleptic Ru(II) and Ir(III) complexes for luminescent sensing and staining specific cell
organelles, including nuclei, nucleoli, mitochondria, lysosome, and endoplasmic reticulum, etc.
In this talk, I will discuss the design strategy and construction of new polypyridine
ligands and their bis-heteroleptic Ru(II) and Ir(III) complexes which show excellent
photophysical/chemical and redox properties. Potential sensing and bioimaging properties in
chemical, environmental and biological samples will also be discussed. |