A derivative of N^ε-benzyloxycarbonyl-L-lysine with a photo-reactive diazirinyl group, N^ε-[((4-(3-(trifluoromethyl)-3H-diazirin-3-yl)benzyl)oxy)carbonyl]-L-lysine, was site-specifically incorporated into target proteins in mammalian cells. The incorporated photo-crosslinker is able to react not only with residues as distant as about 15 Å but also with those in closer proximity, thus enabling “wide-range” photo-crosslinking of proteins.