Tetra(pyrazino[2,3-b] pyrazino) porphyrazines: Synthesis, absorption, photophysical and electrochemical properties of strongly electron-deficient macrocycles
Abstrakt
Highly electron deficient 6,7-disubstituted (tert-butylsufanyl, 2,6-diisopropylphenoxy, diethylamino, 2-pyridyl, 2-thienyl, 2-furyl) pyrazino[2,3-b] pyrazino-2,3-dicarbonitriles were prepared and attempted in cyclotetramerization to corresponding tetra(pyrazino[2,3-b] 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 (lambda(max) = 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 (Phi(F) similar to 0.25, Phi(Delta) similar to 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-b] 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-b] pyrazino-2,3-dicarbonitriles.
TPyzPyzPzs represent an example of the strongest electron-deficient core among the phthalocyanines, naphthalocyanines and their aza-analogs.