Stepwise Synthesis of Tetrabenzotriazaporphyrins (TBTAPs) and Their Open 2- and 3-Ring Fragments

The intermediate structures between phthalocyanines and porphyrins (so-called hybrid structures) are intriguing materials that offer the potential to combine features of each parent, and also offer tunability of properties through modification and further functionalization. We report here the stepwise synthesis of tetrabenzotriazaporphyrins(TBTAPs) bearing different core and meso-aryl substituents. The results are unexpected; our previous results showed that the reaction between aminoisoindoline initiator ("A") and a phthalonitrile ("B") led preferentially to 2:2, ABBA hybrids, presumed to be via reaction between 2x "AB" intermediates. Here we report the synthesis of discrete "AB" fragments and their subsequent reaction chemistry. Reaction of the AB intermediates under typical macrocyclization conditions fails to produce more than a trace of the expected ABBA TBTAP hybrid. Rather, the reactions yield the 3:1 ABBB TBTAPs predominantly, alongside an open ABA trimer (a tripyrrin analogue). The protocol provides a useful alternative synthesis of TBTAPs that minimizes the formation of phthalocyanine side-product. ABA trimer synthesis was separately optimized to produce a short series. The materials show broad absorption across the visible range and assemble into a preferred helical, coiled arrangement as revealed by crystallography.