Formation and Spectroelectrochemical Characterization of Multilayer and Submonolayer Thin Films of 2,3,9,10,16,17,23,24-Octa(2-benzyloxy-ethoxy) Phthalocyninato Copper (CuPc(OC₂OBz)₈)

Abstract

<jats:p> We review here the self-assembly, electrochemical and spectroelectrochemical properties of 2,3,9,10,16,17,23,24-octa(2-benzyloxyethoxy) phthalocyaninato copper ( CuPc ( OC <jats:sub>2</jats:sub> OBz )<jats:sub>8</jats:sub>), where terminal benzyl groups on the eight ethylene oxide side chains assist in forming unusually ordered, mechanically rigid thin films. New spectroscopic characterization of cast CuPc ( OC <jats:sub>2</jats:sub> OBz )<jats:sub>8</jats:sub> films is discussed in comparison with cast films of its metal-free analogue H <jats:sub>2</jats:sub> Pc ( OC <jats:sub>2</jats:sub> OBz )<jats:sub>8</jats:sub> and similar copper and dihydrogen phthalocyanines with benzyl — terminated triethylene oxide substituents, CuPc (( OC <jats:sub>2</jats:sub> O )<jats:sub>3</jats:sub> Bz )<jats:sub>8</jats:sub>, and H <jats:sub>2</jats:sub> Pc (( OC <jats:sub>2</jats:sub> O )<jats:sub>3</jats:sub> Bz )<jats:sub>8</jats:sub>, which do not demonstrate the same degree of ordering as CuPc ( OC <jats:sub>2</jats:sub> OBz )<jats:sub>8</jats:sub>. AFM studies of horizontally transferred LB films of CuPc ( OC <jats:sub>2</jats:sub> OBz )<jats:sub>8</jats:sub> show column–column distances of ca 2.8 nm and confirm the high degree of ordering previously surmised from spectroscopic characterization of multilayer thin films. The oxidative electrochemistry of multilayer thin films prepared from these Pcs is strongly dependent on the chemical identity of the supporting electrolyte anion and on annealing of the thin films. Compliance of the films to counter-ion transport limits the extent of electrochemical doping. Preliminary studies of the oxidative electrochemistry of isolated CuPc ( OC <jats:sub>2</jats:sub> OBz )<jats:sub>8</jats:sub> aggregates (diluted into an electroinactive methyl arachidate thin film) on an electroactive, integrated optic waveguide (EA-IOW) are also presented. Monitoring the change in absorbance at 633 nm on the waveguide surface allows the determination of the onset potential for oxidation of the isolated aggregates, which appears to be less positive in potential versus that observed for multilayer Pc assemblies. </jats:p>