A novel soluble tetranuclear copper(I) cluster containing an unsubstituted mu(4)-selenido moiety, [Cu-4(mu-dppm)(4)(mu(4)-Se)](2+) (1), has been synthesized and characterized by X-ray crystallography. Its photophysical and electrochemical properties have been studied. It is envisaged that the emissions of 1 are associated with a ligand-to-metal charge-transfer LMCT [(Se2-) --> Cu-4] triplet excited state, and probably with mixing of a metal-centered (3d(9)4s(1)) Cu(I) state. The phosphorescent state of 1 undergoes facile electron-transfer quenching with a series of pyridinium accepters. An excited-state reduction potential, E degrees[Cu-4(mu-dppm)(4)(mu(4)-Se)(3+/2+*)], of -1.55(10) V vs SSCE has been estimated. Crystal data : monoclinic, space group C2/c (No. 15), a = 27.913(9) Angstrom, b = 16.512(9) Angstrom, c = 24.10(1) Angstrom, beta = 109.29(2)degrees, V = 10483(5) Angstrom(3), Z = 4.