The synthesis and physicochemical properties of a novel diazepinoporphyrazine possessing G1-dendrimeric substituents are presented. Initially, diaminomaleonitrile was condensed with 1,3-bis-(4-hydroxyphenyl)-1,3-propanedione to give a novel 1,4-diazepine-2,3-dicarbonitrile derivative which was subjected to an alkylation reaction with 3,5-bis(benzyloxy)benzylbromide furnishing a 1,4-diazepine-2,3-dicarbonitrile derivative with bulky substituents. Subsequent macrocyclization led to the desired diazepinoporphyrazine with conjugated, hyperbranched G1-dendrimeric substituents, which was characterized by MS MALDI and NMR. The potential photosensitizing activity of the novel porphyrazine was evaluated by measuring its ability to generate singlet oxygen. This measurement was performed with and without addition of the anti-aggregation agent tetramethylamonium fluoride to determine the role of the monomeric form in singlet oxygen generation.