Spectral-luminescence, redox and photochemical properties of AlIII, GaIII and InIII complexes formed by peripherally chlorinated phthalocyanines and tetrapyrazinoporphyrazines

Abstract

Complexes of Al[Formula: see text], Ga[Formula: see text] and In[Formula: see text] with peripherally chlorinated phthalocyanine (Cl8PcM) and tetrapyrazinoporphyrazine (Cl8TPyzM) were prepared and studied using spectral and electrochemical methods. DFT calculations were used to reveal the peculiarities of their molecular and electronic structure. Peripheral chlorination of phthalocyanine complexes increases their electron affinity and the first reduction of [Cl8PcM] is observed at −0.25 – −0.35 V (by 0.2 – 0.3 V easier than for [PcM]). Additional azasubstitution further increases the acceptor properties of the macrocycle and [Cl8TPyzM] are reduced at −0.16 V. Among [Cl8PcM] only the Ga[Formula: see text] complex is stable to photooxidation, while among [Cl8TPyzPzM] it is the only one undergoing photoreduction. Fluorescence quantum yields ([Formula: see text] and lifetimes ([Formula: see text] as well as the ability to generate singlet oxygen ([Formula: see text] were determined. The [Formula: see text] values show typical dependence on the central metal Al > Ga >> In and are decreased upon the introduction of chlorine atoms in the peripheral and especially in the axial position. At the same time, azasubstitution in the benzene ring has a minor influence on the [Formula: see text] values but strongly shortens [Formula: see text] (from ca 6 to ca 2 ns). The Ga[Formula: see text] complexes have the highest ability to generate 1O2 and can be considered as effective photosensitizers, especially [Cl8TPyzPzGa(OH)] ([Formula: see text] = 0.87 in slightly acidified solution). Spectral properties in a strongly acid medium were also studied and it was observed that [Cl8PcM] are consequently protonated on meso-nitrogens.