Bis-phthalimide intermediates of the formula: ##STR1## wherein one of R.sup.9 and R.sup.10 is hydrogen and the other is --NR.sup.11 R.sup.12 ; R.sup.11 is hydrogen or straight stain alkyl containing 1-4 carbon atoms and R.sup.12 is ##STR2## wherein n=1-3. The compounds are intermediates in the synthesis of chemiluminescent-labeled conjugates which are useful as reagents in specific binding assays for determining ligands or their specific binding partners in liquid media.