Phthalocyanines with eight oligo(ethylene oxide) alkoxy units: thermotropic phase behavior, aggregate formation and ion complexation with redox-active ions

Abstract

The thermotropic phase behavior of phthalocyanines (Pcʼs) with eight oligo(ethylene oxide) alkoxy side chains has been investigated. An increase in the number of ethylene oxide units results in a decrease in the solid-to-mesophase and isotropization temperatures. The investigated compounds display a discotic hexagonally ordered (D ho ) mesophase. The solubilization of LiI/I 2 into the polar side chains of the Pcʼs has been studied both in solution and in spin-coated films, and the effect on the aggregate formation is discussed. At higher temperatures, the Pc -LiI/I 2 complex is not stable and small crystallites are formed. The dark direct current conductivity of these films is reported as a function of LiI/I 2 concentration in the polar side groups of the Pcʼs. The observed decrease in conductivity with increasing salt concentration is related to the morphology of the material.

Porphyrazines with oligo(ethylene oxide) thio alkoxy chains: Synthesis, aggregation, photophysics, and complexation with redox-active ions

“…Separation of the redox couple occurs at ca 115 °C for all three free-base porphyrazines. This sheds light on an observation made for similarly substituted phthalocyanine -LiI/I 2 composites [10]. These rapidly form LiI crystals upon passing from the mesophase into the isotropic phase, which in those cases take place at temperatures higher than 115 °C.…”

“…Contrary to phthalocyanines with the same substituents [10], mixing of 1a-c with LiI/I 2 did not result in an immediate loss of phase transitions for the 1:1 and 1:2 mixtures (molar ratios) for 1a-1c, while for 1c phase transitions were still observable with even the 1:3 mixture. In general, a gradual slight decrease and broadening of the phase transition temperature range and a decrease of the accompanying enthalpies is observed for all three free-base porphyrazines.…”

“…These calorimetric data show that incorporation of ethylene oxide moieties at the hexyloxy substituents results in a gradual decrease of the phase transition temperatures, with complete loss of the liquid crystallinity. This behavior contrasts with that of phthalocyanines that are substituted with the same peripheral groups, which still display liquid crystalline phases [10]. The decrease in transition temperatures is probably caused by an increased geometrical disorder due to the lone pair -lone pair repulsions occurring at the oxygen atoms.…”

“…It has recently been shown in our laboratories that the LiI/I 2 redox couple can successfully be solubilized into phthalocyanines bearing ethylene oxide units without influencing the self-aggregating properties of the macrocycles, and obtaining a high charge mobility [10]. Variation in the number of ethylene oxide units allows for fine-tuning of the phase transition temperatures that are not significantly altered by the presence of the solubilized electrolyte.…”