Axial coordination reactions with nitrogenous bases and determination of equilibrium constants for zinc tetraarylporphyrins containing four β,β′-fused butano and benzo groups in nonaqueous media

Abstract

The axial coordination properties of six zinc tetraarylporphyrins with seven different nitrogenous bases were examined in CH2Cl2 for derivatives containing four [Formula: see text],[Formula: see text]-fused butano or benzo groups and the equilibrium constants (log[Formula: see text] determined using spectral titration methods. The examined compounds are represented as butano(YPh)4PorZn and benzo(YPh)4PorZn, where Por is the porphyrin dianion and Y is a CH3, H or Cl substituent on the para-position of each meso-phenyl ring of the macrocycle. The initial four-coordinate butano- and benzoporphyrins will axially bind one nitrogenous base to form five-coordinate derivatives in CH2Cl2 and this leads to a 4–22 nm red-shift of the Soret and Q bands. The log[Formula: see text] values range from 1.98 to 4.69 for butano(YPh)4PorZn and from 3.42 to 5.36 for benzo(YPh)4PorZn, with the exact value depending upon the meso and [Formula: see text]-substituents of the porphyrin and the conjugate acid dissociation constants (p[Formula: see text] of the nitrogenous base.

Impact of photosensitizer orientation on the distance dependent photocatalytic activity in zinc phthalocyanine–nanoporous gold hybrid systems

“…Such a redshi of the Q-band of phthalocyanines and porphyrins is known to be caused by axial coordination of a nitrogen atom from an organic amine. [41][42][43][44] The binding of an additional ligand in axial position is a common feature of zinc phthalocyanines and porphyrins derivatives, even forming stable crystal structures, supramolecular dimers and trimers as well as hybrid systems directly immobilized on amine-terminated SAMs. [45][46][47][48][49][50][51][52][53] In addition, the penta-coordinating ability of the Zn central ion of zinc porphyrins is used frequently as template in many supramolecular synthesis approaches.…”