First Subphthalocyanine Analogue with Fused 6H‐1,4‐diazepine Ring and its Conversion to Aminobenzamide Derivative

Abstract

AbstractMixed cyclization of 5,7‐diphenyl‐6H‐1,4‐diazepine 2,3‐dicarbonitrile and tetrafluorophthalonitrile in the presence of boron trichloride affords along with symmetrical perfluorinated subphthakocyanine, [F12sPc], two novel subporphyrazine‐type products which were isolated by column chromatography and characterized by mass‐sprectometry, NMR, IR, UV‐VIS and fluorescent spectroscopy. It was established that co‐cyclomerization of dinitriles is accompanied by electrophilic chlorination of 1,4‐diazepine ring by evolved Cl2 resulting in formation of dibenzosubporphyrazine [F8sPc1] with fused 6‐chloro‐5,7‐diphenyl‐6H‐1,4‐diazepine fragment. According to DFT modelling and 1H NMR data, a more stable diastereomer with an axial Cl atom is formed and no inversion of the 1,4‐diazepine ring is observed. Hydrolytic cleavage of the 1,4‐diazepine fragment in [F8sPc1] is observed upon chromatography or in the presence of a strong acid (CF3COOH) and leads to 2‐amino‐3‐benzamide substituted dibenzo subporphyrazine [F8sPc2]. Fluorescence of [F8sPc1] (ΦF=0.03) is ca 10 times lower than for [F12sPc] (ΦF=0.28) due to the combined effect of intramolecular charge transfer (ICT) from the donor diazepine ring to the acceptor sPc macrocycle and heavy atom effect of chlorine. Fluorescence of [F8sPc2] is almost completely quenched by ICT from −NH2 group to the electron‐deficient subporphyrazine core (ΦF<0.001), but addition of acid leads to protonation of the amino group and switch‐ON the fluorescence. Therefore, aminobenzamide substituted subporphyrazines can be considered as perspective pH‐sensitive fluorophores.