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.