Two-dimensional “nano-ring and nano-crystal” morphologies in Langmuir monolayer of phthalocyaninato nickel complexes

Three 1,8,15,22-tetrasubstituted phthalocyaninato nickel complexes Ni[Pc(α-OR)4] [H2Pc(α-OC5H11)4 = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine; H2Pc(α-OC7H15)4 = 1,8,15,22-tetrakis(2,4-dimethyl-3-pentyloxy)phthalocyanine; H2Pc(α-OC10H7)4 = 1,8,15,22-tetrakis(2-naphthyloxy)phthalocyanine] (1–3) have been prepared by treating the corresponding metal-free phthalocyanines H2Pc(α-OR)4 with Ni(acac)2⋅2H2O in refluxing n-pentanol. Structures of the Langmuir monolayers of these compounds at different temperature have been investigated. Compound 1 formed nano-ring structures with the outer diameter of 70–150 nm and inner diameter of 50 nm at 25.0 °C while 2 and 3 formed round particles. This difference can be ascribed to the different substituents at α position. The morphologies of the aggregates of 1 in monolayers have been found to change with temperature. Decreasing in temperature induced the formation of regular quadrate crystals. UV–vis absorption spectra revealed strong intermolecular interactions in the nano-ring aggregates. Polarized UV–vis absorption spectra suggest a titled orientation with respect to the surface of substrate for phthalocyanine macrocycles in the nano-ring aggregates.

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