Mixed-ligand Cu(I) complexes have attracted attention as alternatives to the noble- and/or rare-metal complexes, because of their remarkable photofunctions. To develop mixedligand Cu(I) complexes with rich photoftinctions, an investigation of a suitable combination of ligands has captured more and more research interests. Herein, we report the first examples of emissive heteroleptic diphosphine-distilfide Cu(I) complexes combined with Pdi hosphine ligands. The systematic study using a series of diphosphine ligands revealed that large it-conjugated bridging moieties between the two P atoms in the diphosphine ligands result in higher light-emission performance. When the diphosphine ligand was (R)-BINAP ((R)-BINAP = (R)-(+)-2,2'-bis(diphenyliitiosphino)-1,1'-binaphthyl), the Cu(I) complex had an em is lifetime (tau(em) = 118 mu s).