Octakis(2-benzyloxyethylsulfanyl) Copper (II) Phthalocyanine: A New Liquid Crystalline Discotic Material with Benzyl-Terminated, Thioether-Linked Side Chains

Abstract

The synthesis and materials properties of a new liquid crystalline phthalocyanine, octakis (2-benzyloxyethylsulfanyl) copper (II) phthalocyanine, 2, are reported. This phthalocyanine possesses eight benzyl-terminated side chains with thioether links to the Pc core, which promote greater interaction between the discotic mesogens than has been seen in previous Pcs reported from this group which had benzyl-terminated alkoxy-based side chains. The use of thioether links to these side chains promotes a red-shift in the Q-band absorbance spectrum, small decreases in first oxidation potential, increased solution aggregation constants, and significantly higher K→LC transition temperatures than seen in conventional alkoxy-based side-chain-modified Pcs. Powders and single crystals of this material were characterized by X-ray diffraction and found to represent two closely related polymorphs. Room-temperature XRD of powders of 2 showed a monoclinic unit cell: a = 22.81(1) Å, b = 9.780(5) Å, c = 19.314(6) Å, α = 90°, β = 106.918(14)°, γ = 90°, V = 4472 Å3, two molecules per unit cell, with a helical twist of the Pcs along the b-axis. The packing architecture in these powders showed a transition to an oblique (distorted rectangular, Colrd) phase at temperatures in the LC regime, which was reversible upon cooling. The single-crystal diffraction data showed a monoclinic unit cell: a = 23.911 (18) Å, b = 5.224(3) Å, c = 39.17(3) Å (c ≈ √3a); α = 90°, β = 96.971(14)°, γ = 90°, volume = 4903(8) Å3, and AFM characterization of the 〈001〉 plane of these single crystals clearly showed evidence for layered growth in this material. Langmuir−Blodgett films of 2, characterized by AFM, X-ray reflectivity, and X-ray diffraction, showed hexagonal close packing of parallel Pc columns in the as-deposited film, and upon annealing, showed formation of at least two different domains, with column−column spacings of ca. 21 Å and 26 Å, corresponding to the 〈10〉 and 〈01〉 faces of a 2D lattice, closely related to the unit cell found for the polycrystalline material.