Azines of porphyrinoids. Does azine provide conjugation between chromophores?

A new approach to functionalize porphyrinoids was developed based on the Vilsmeier formylation followed by the azine formation and a new class of the compounds namely azines of porphyrinoids was obtained. Variously substituted azine porphyrins, chlorins and their dyads were synthesized, and their structural and electronic parameters were studied with X-ray diffraction analysis, electronic absorption and emission spectra, electrochemistry and DFT calculations. Azine represents a very peculiar bridge with an unclear conjugation ability affecting optical properties of chromophores. This work was aimed to reveal azine properties and the influence of the azine bridge on the chromophores linked. The results of investigation allowed to conclude that azine bridge can partly be regarded as a conjugation switch with a high threshold level of switching, where limited conjugation in the ground state can be greatly increased at higher energy states of the azine molecule.