Complex formation of phthalocyanine derivatives substituted by polyethylene oxide with alkali metal ions in methanol

Abstract

Amphiphilic bifunctional phthalocyanine (Pc) derivatives (protonated compound: EO–H2Pc and copper(II) complex: EO–CuPc) having methylhexaethylene oxide (EO: –O(CH2CH2O)6–CH3) have been synthesized. Dimerization equilibria of EO–H2Pc in alcohols and complex formation with alkali metal ion (Li+, Na+, and K+) in methanol have been studied by means of absorption and fluorescence spectrophotometry. EO–H2Pc in methanol exists predominantly as a dimer, (EO–H2Pc)2. By the reaction with alkali metal hydroxide, the dimer dissociates to monomer and forms complexes at the Pc moiety and/or EO moiety. Lithium ion is captured inside the cavity of the Pc ring and forms a stable complex, EO–LiPc−. Sodium ion and potassium ion, the ion sizes of which are larger than the cavity size of Pc, form “sitting a top” (SAT) complex, that is, the metal ion in the complex with Pc moiety is located on the outside of the Pc ring. By the reaction with NaOH, sodium ion is inserted between the dimeric Pc ring, (EO–Na1/2Pc)2 at the first step, then forms a monomeric 1:1 complex, EO–NaPc−. In the case of reaction with KOH, the monomeric complex, in which potassium ion is coordinated at the EO moiety, (KEO)+H2Pc, is formed as the first step. Then, the Pc moiety coordinates to the potassium ion, (KEO)+–KPc−. The structures of complexes were confirmed by the reaction of EO–CuPc. The order of stability of alkali metal ion complex is obtained as Li+ > > Na+ > K+ for Pc moiety and Li+ < Na+ < < K+ for EO moiety.