Three 1,8,15,22-tetrasubstituted phthalocyaninato nickel complexes Ni[Pc(alpha-OR)(4)] [H2Pc(alpha-OC5H11)(4) = 1,8,15,22-tetrakis(3-pentyloxy)-phthalocyanine- H2PC(alpha-OC7H15)(4) = 1,8,15,22-tetrakis(2,4-dimethyl-3-pentyloxy)phthalocyanine; H2PC(alpha-OC10H7)(4) = 1,8,15,22-tetrakis-(2-naphthyloxy)phthatocyanine] (1-3) have been prepared by treating the corresponding metal-free phthalocyanines H2PC(alpha-OR)(4) with Ni(acac)(2)center dot 2H(2)O 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 degrees C while 2 and 3 formed round particles. This difference can be ascribed to the different substituents at alpha position. The morphologies of the aggregates of I 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. (c) 2006 Elsevier Inc. All rights reserved.