Thin films of polymerized rodlike phthalocyanine aggregates

We report here the synthesis, characterization, and thin film formation of a polymerizable octa-substituted phthalocyanine (Pc) with styryl-terminated side chains, CuPc(OCH₂CH₂OCH₂CH=CHPh) ₈, 2,3,9,10,16,17,23,24-octakis(2-cinnamyloxyethoxy) phthalocyaninato copper(II) (1). We compare this Pc with a previously discussed phthalocyanine, also possessing styryl groups at the termini of the side chains, but with one alkoxy group in the side chain removed, CuPc(OCH ₂CH₂CH=CHPh)₈ (2) (J. Am. Chem. Soc. 2001, 123, 3595). Both 1 and 2 are related to the octa-substituted phthalocyanine CuPc(OCH₂CH₂OBz)₈, 2,3,9,10,16,17,23, 24-octakis (2-benzyloxyethoxy) phthalocyaninato copper(II) (3), which has been shown to form highly coherent rodlike aggregates in Langmuir-Blodgett (LB) films, with excellent control of rod orientation (J. Am. Chem. Soc. 1999, 121, 8628; Langmuir 2001, 17, 7071). Irradiation of the styryl π-π* absorbance bands (254 nm) for horizontally transferred LB films of 1 and 2 results in stabilization of their rodlike aggregates, through formation of cyclobutane links between adjacent side chains. Compound 1 shows a maximum 75% conversion of styryl groups versus ca. 55% conversion in 2. Polymerized thin films of 1 are insoluble in common solvents, and "ribbonlike" features can be lithographically produced with widths of 8 microns and heights of ca. 20 nm, maintaining control over the orientation of the Pc rods in the patterned features. Long-range order in both the as-deposited, annealed, and polymerized thin films was confirmed by atomic force microscopy and X-ray reflectometry, and small differences in the orientation of individual Pc's, between films of 1 and 3, were determined by transmission and reflectance Fourier transform infrared spectroscopy. Higher dark and photoconductivities and higher electrical anisotropies were observed in films of 1, after annealing and polymerization, versus those seen for films of 3.