Nanocomposites of metallophthalocyanines and conjugated Polymers
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OF
METALLOPHTHALOCYANINES
AND
CONJUGATED
SHUJIAN YI AND SAMSON A. JENEKHE Departments of Chemical Engineering and Chemistry University of Rochester, Rochester, New York 14627-0166
ABSTRACT Nanocomposites of phenoxy-substituted vanadyl phthalocyanine with a t-conjugated polymer, poly(benzimidazobenzophenanthroline ladder), have been prepared from their Lewis acid complexes in organic solvents. The resulting composite thin films obtained by spin-coating have excellent optical transparency and interesting composition-dependent morphology and photoelectronic properties. Enhanced photoconductivity, compared to the components, was observed in some composites with discrete nanoscale metallophthalocyanine aggregates. INTRODUCTION Organic materials, such as metallophthalocyanines (MPc), squaraines, perylenes, and azo compounds, are of interests for applications in photoelectronic devices. Among these materials, metallophthalocyanines are most attractive because of their broad spectral responses and high photosensitivities.' For instance, pigments of titanylphthalocyanine have been reported to have one of the best photosensitivities (0.2 gJ/cm2) among organic photoconductors.2 However, because most unsubstituted metallophthalocyanines have poor processibility as a result of their very limited solubility, organic photoconductors are usually prepared by dispersing fine particles of metallophthalocyanine pigments in an insulating polymer matrix. 3 The pigment particles, after wet milling, typically have sizes of several hundred nanometers in diameter. 4 Since the inert polymer matrix is not photoactive nor charge-transporting, it may contain traps that impede charge transport. 5 The use of active polymer matrix may improve the performance of photoconductors. Moreover, there is interest in new photoconductors with sensitivity over a wide spectral range, i.e., with photosensitivity in both the visible and the nearIR region.6 Approaches to such materials include the combination of pigments with similar or dissimilar structures, 6 and the dispersion of pigment particles in a photoconductive polymer 5 matrix. Nanoscale size effects on the photoconductivity of nanocomposites and conjugated polymers were recently reported.7,8 Here, we report the preparation and the photoconductive properties of novel nanocomposites consisting of tetraphenoxy-substituted vanadyl phthalocyanine (VOTPPc) and a conjugated polymer, poly(benzimidazobenzophenanthroline ladder)(BBL) (Figure 1). Our measurements show that some of the composites have an enhanced quantum efficiency of photogeneration and photosensitivity when the dispersed VOTPPc phase is in the nanoscale size range.
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Mat. Res. Soc. Symp. Proc. Vol. 488 c 1998 Materials Research Society
EXPERIMENTAL SECTION Materials. The polymer BBL with an intrinsic viscosity of 32 dL/g in methanesulfonic acid at 30TC was synthesized in this laboratory, using the literature method. 9 Nitromethane (-96%), Gallium (III) chloride (GaC13 , -99.999%), and vanadyl 2,9,16,23-tetraphenoxy-29H,31Hphthalocya
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