New dinuclear copper(I) complexes [Cu-2(mu-X)(2)(mu-1,8-naphthyridine)-(PPh3)(2)] (X = I, Br) having the butterfly-shaped {Cu-2(mu-X)(2)} unit show red phosphorescence at room temperature in the solid state. Molecular orbital calculations show that the emissions of the new complexes are not directly related to their short Cu center dot center dot center dot Cu separations [2.6123(5) and 2.6271(4) angstrom] and are assignable to the triplet charge-transfer excited states from the {Cu-2(mu-X)(2)} core to 1,8-naphthyricline.