Tetra(pyrazino[2,3-b]pyrazino)porphyrazines: Synthesis, absorption, photophysical and electrochemical properties of strongly electron-deficient macrocycles

Abstract

Highly electron deficient 6,7-disubstituted (tert-butylsufanyl, 2,6-diisopropylphenoxy, diethylamino, 2-pyridyl, 2-thienyl, 2-furyl) pyrazino[2,3-[Formula: see text]]pyrazino-2,3-dicarbonitriles were prepared and attempted in cyclotetramerization to corresponding tetra(pyrazino[2,3-[Formula: see text]]pyrazino)porphyrazines (TPyzPyzPzs). Only the template reaction in pyridine with zinc acetate and only for the compounds substituted with tert-butylsulfanyl or 2,6-diisopropylphenoxy substituents resulted in efficient cyclotetramerization. Absorption spectra of these zinc TPyzPyzPzs indicated considerable blue shift of the main absorption Q-band ([Formula: see text] 693 nm and 669 nm in pyridine for tert-butylsulfanyl or 2,6-diisopropylphenoxy derivatives) when compared to other aza-analogs of naphthalocyanines. Photophysical parameters ([Formula: see text] [Formula: see text] 0.25, [Formula: see text] [Formula: see text] 0.65) seemed to be unaffected by change of the macrocycle core and only slightly by different peripheral substituents in agreement with heavy-atom effect. Electrochemical data revealed strong electron-deficient character of hetaryl disubstituted pyrazino[2,3-[Formula: see text]]pyrazino-2,3-dicarbonitriles. The first reduction potentials of tert-butylsulfanyl or 2,6-diisopropylphenoxy substituted zinc TPyzPyzPzs were even more cathodically shifted when compared to their corresponding pyrazino[2,3-[Formula: see text]]pyrazino-2,3-dicarbonitriles. TPyzPyzPzs represent an example of the strongest electron-deficient core among the phthalocyanines, naphthalocyanines and their aza-analogs.