Correlation between the Fluorination Degree of Perfluorinated Zinc Phthalocyanines, Their Singlet Oxygen Generation Ability, and Their Photoelectrochemical Response for Phenol Sensing.

Electron-withdrawing perfluoroalkyl peripheral groups grafted on phthalocyanine (Pc) macrocycles improve their single-site isolation, solubility, and resistance to self-oxidation, all beneficial features for catalytic applications. A high degree of fluorination also enhances the reducibility of Pcs and could alter their singlet oxygen (1O2) photoproduction. The ethanol/toluene 20:80 vol % solvent mixture was found to dissolve perfluorinated FnPcZn complexes, n = 16, 52, and 64, and minimize the aggregation of the sterically unencumbered F16PcZn. The 1O2 production ability of FnPcZn complexes was examined using 9,10-dimethylanthracene (DMA) and 2,2,6,6-tetramethylpiperidine (TEMP) in combination with UV-vis and electron paramagnetic resonance (EPR) spectroscopy, respectively. While the photoreduction of F52PcZn and F64PcZn in the presence of redox-active TEMP lowered 1O2 production, DMA was a suitable 1O2 trap for ranking the complexes. The solution reactivity was complemented by solid-state studies via the construction of photoelectrochemical sensors based on TiO2-supported FnPcZn, FnPcZn|TiO2. Phenol photo-oxidation by 1O2, followed by its electrochemical reduction, defines a redox cycle, the 1O2 production having been found to depend on the value of n and structural features of the supported complexes. Consistent with solution studies, F52PcZn was found to be the most efficient 1O2 generator. The insights on reactivity testing and structural-activity relationships obtained may be useful for designing efficient and robust sensors and for other 1O2-related applications of FnPcZn.

The influence of intermolecular coupling on electron and ion transport in differently substituted phthalocyanine thin films as electrochromic materials: a chemistry application of the Goldilocks principle.

The transport of both electrons and ions in organic mixed ionic and electronic conductors such as phthalocyanines, is essential to allow redox reactions of entire films and, hence, to impart electrochromism. Thin films of a new type, tetrakis-perfluoroisopropyl-perfluoro phthalocyanine, F40PcCu of different thicknesses were obtained via vapor deposition. The extent of the intermolecular coupling within the F40PcCu films established by van der Waals interactions was investigated by in situ optical spectroscopy during film growth. The transfer of electrons and diffusion of counter cations in these films, as well as their electrochromic performance were characterized by electrochemical and spectroelectrochemical measurements with an aqueous solution of KCl as electrolyte. A moderate degree of intermolecular interaction of the F40PcCu molecules in the solid state was observed, compared to non-fluoroalkylated perfluoro phthalocyanine, F16PcCu and octakis-perfluoroisopropyl-perfluorophthalocyanine, F64PcCu, which exhibit stronger and weaker coupling, respectively. The replacement of F by perfluoroisopropyl is, thereby, established as a valuable approach to tune this coupling of chromophores and, hence, the transport coefficients of electrons and ions in the solid films. Reversible changes of the films upon reduction and intercalation of K+ counter ions and re-oxidation and expulsion of the counter ions were confirmed by simultaneously measured optical absorption spectra. Thin films of F40PcCu showed a well-balanced, equally fast transport of electrons and ions. The films provided a fast and reversible switching process over at least 200 cycles indicating the stability of these materials.