Remarkable Luminescence Behaviors and Structural Variations of Two-Coordinate Gold(I) Complexes -- From Photoinduced Charge Separation to Light-driven Molecular Machines -- Metal-based Photoswitches Derived from Photoisomerization -- Transition Metal Complexes for Photovoltaic and Light Emitting Applications -- Conjugates of Heme-Thiolate Enzymes with Photoactive Metal-Diimine Wires -- Luminescent Transition Metal Complexes as Biological Labels and Probes.