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(OCH<INF>2</INF>CH<INF>2</INF>OCH<INF>2</INF>CH&dbd;CHPh)<INF>8</INF>, 2,3,9,10,16,17,23,24-octakis(2-cinnamyloxyethoxy) phthalocyaninato copper(II) (<BO>1</BO>). 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<INF>2</INF>CH<INF>2</INF>CH&dbd;CHPh)<INF>8</INF> (<BO>2</BO>) (J. Am. Chem. Soc. <BO>2001</BO>, 123, 3595). Both <BO>1</BO> and <BO>2</BO> are related to the octa-substituted phthalocyanine CuPc(OCH<INF>2</INF>CH<INF>2</INF>OBz)<INF>8</INF>, 2,3,9,10,16,17,23,24-octakis (2-benzyloxyethoxy) phthalocyaninato copper(II) (<BO>3</BO>), 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. <BO>1999</BO>, 121, 8628; Langmuir <BO>2001</BO>, 17, 7071). Irradiation of the styryl π−π* absorbance bands (254 nm) for horizontally transferred LB films of <BO>1</BO> and <BO>2</BO> results in stabilization of their rodlike aggregates, through formation of cyclobutane links between adjacent side chains. Compound <BO>1</BO> shows a maximum 75% conversion of styryl groups versus ca. 55% conversion in <BO>2</BO>. Polymerized thin films of <BO>1</BO> 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 <BO>1</BO> and <BO>3</BO>, were determined by transmission and reflectance Fourier transform infrared spectroscopy. Higher dark and photoconductivities and higher electrical anisotropies were observed in films of <BO>1</BO>, after annealing and polymerization, versus those seen for films of <BO>3</BO>.