Effect of air-absorbed oxygen and moisture on the chemical stability of photoexcitedMg,ZnandEuphthalocyanines in dimethylformamide

Abstract

Absorption of oxygen and moisture from air by MPc-DMF systems was studied and related to the molecular stability demonstrated by phthalocyanine complexes (unsubstituted MPc's : MgPc , ZnPc and EuPc2; Pc = phthalocyanine ligand, C32H16N8) subjected to UV irradiation. A lower stability of air-exposed dimethylformamide solutions is observed and is due to a specific affinity for molecular oxygen revealed by the Pc macrocycle. SEM results proved oxygen molecules fixed to the phthalocyanine solids by forces strong enough to sustain desorption under vacuum. Absorption curves determined for MPc-DMF systems also indicate oxygen accommodated by the phthalocyanine moiety. This explains the predominantly oxygen-mediated photolysis, as well as the very short fluorescence lifetimes of metal phthalocyanines. The effect of air-absorbed moisture on the photostability is much less pronounced and practically insignificant for concentrations of H2O lower than 1%. An apparent stabilizing effect of water was observed and elucidated basing on kinetic considerations. The degradation rate of the photoexcited phthalocyanine moiety in air-exposed solutions depends on individual chemical properties and the molecular structure of the complex. EuPc2proved very stable whereas the photostability of ZnPc and MgPc gradually decreased in the course of time.

Sulfur Dioxide Oxidation Catalyzed by Photosensitized Ytterbium Diphthalocyanine

“…The explored concentration range of the both components has been reported in Table 1 along with other parameters concerning the studied process. Under these conditions, the average molar ratio of air-absorbed O 2 to SO 2 was close to 1:1 or higher [9].…”

“…In general, these different colored species are considered either diverse red-ox compounds [18] and/or protonated molecules [19]. In our previous works we have suggested, that such changes may be induced e.g., by electron acceptors which may affect the macrocycles in LnPc 2 [8,9]. To maintain the unity of the overall sandwich bonding system, the electronic density must be re-distributed in such a way that aromacity of the both phthalocyanine cores could be preserved.…”

“…Free molecular oxygen was present in the system due to natural absorption from air by DMF as well as introduced by the phthalocyanine substrate during preparation of YbPc 2 solutions (for details see [9]). SO 3 was qualitatively detected in the post-reaction solution by applying a simple copper-test.…”

“…The potential revealed by these compounds seems particularly interesting for projects focused on environment-related objectives, such as clean technologies as well as those concerning pollution problems. The principal advantage of rare earth diphthalocyanines, compared to other metallophthalocyanines is a considerable photostability they have demonstrated both in the solid state and in organic solvents, despite the presence of oxygen and water [8][9][10].…”

Phthalocyanine Photoregeneration for Low Power Consumption Chemiresistors

“…18 In either case, the interaction results in a change of resistance (and impedance) that can be correlated with analyte concentration. 19 Regarding the gas-sensing characteristics of Pc films, their morphology also plays a significant role.20 The most familiar phthalocyanine polymorphs are α, β, χ, and τ. The first two, the α and β forms, are common in phthalocyanine thin films.15,21 In particular, NO2 detection by various Pc morphologies was reported in ref 22.…”