Structural investigations of homometallic di-and tri-nuclear coinage metal complexes with bridging phosphine ligands, [M 2 (P ∩ P) 2 ]X 2 and [M 3 (P ∩ P ∩ P) 2 ]X 3 (M = Cu(I), Au(I), and Ag(I); X = anion), have revealed close intramolecular metal-metal and metal-anion contacts in their crystal lattices, thus providing solid-state evidence for metallophilicity and metal-substrate interactions in two-coordinate d 10 metal ions. To verify the existence of weak closed-shell metal-metal interactions, UV-vis absorption and resonance Raman spectroscopic techniques have been employed. Comparisons of the absorption spectra of [M 2 (P ∩ P) 2 ] 2+ and [M 3 (P ∩ P ∩ P) 2 ] 3+ show that the spin-and dipole-allowed [nd * → (n + 1)p] transition red-shifts in energy from [M 2 (P ∩ P) 2 ] 2+ to [M 3 (P ∩ P ∩ P) 2 ] 3+ . This spectral assignment was confirmed by resonance Raman spectroscopy, which reveals stronger metal-metal interaction in the 1 [(n + 1)p, nd * ] state compared to the ground state. Photoluminescence from the 3 [(n + 1)p, nd * ] excited state was also recorded for the [M 2 (P ∩ P) 2 ]X 2 and [M 3 (P ∩ P ∩ P) 2 ]X 3 solids, where X is a non-coordinating anion. The spectroscopic data for these metal-centered transitions are supported by theoretical calculations. Perturbations of the M M bonded excited states through interaction with neighboring solvent molecules or anions lead to exciplex formations with emission in the visible region. The sensitivity of photoluminescence of two-coordinate d 10 metal complexes to metal-ligand coordination provides an entry to new classes of luminescent sensory materials for substrate-binding processes. The 3 [(n + 1)p, nd * ] excited states of [M 2 (P ∩ P) 2 ] 2+ (M = Cu and Au) systems are powerful reductants and light-induced multi-electron photocatalysis by these systems have been observed.