Preparation and Luminescence Properties of Organic Thin Films Obtained by Vacuum Deposition of Poly(p-phenylene) Synthesized by Various Chemical Methods

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Abstract
Various organic thin films were obtained by vacuum deposition of poly(p-phenylene) (PPP) synthesized by three different methods: Grignard coupling of p-dibromobenzene (PPP-Y), and two kinds of oxidative cationic polymerization of benzene (PPP-K by a CuCl2–AlCl3 system and PPP-T by a CuCl–AlCl3–O2 system). The IR absorption band at 760 cm−1, which is attributed to a mono-substituted benzene ring, was stronger for the PPP thin films than that for the original PPP. The deposited thin films were partially soluble in THF and chloroform. The electronic absorption spectra of the PPP-K and the PPP-T thin film solutions had shoulders near 410 nm, while that of the PPP-Y film did not. The emission spectra had a peak at 375 nm for the PPP-K and the PPP-Y solutions. In contrast, the PPP-T solution had emission peaks at 465 and ca. 500 nm in addition to a peak at 380 nm, and the excitation spectrum for the peak at 465 nm was quite different from that for the peak at 380 nm. As for thin films, the PPP-K and the PPP-Y had emission peaks at 400—500 nm, while the PPP-T had an emission peak at 615 nm in addition to the peaks at 400—500 nm. The difference in the emission spectra is discussed in terms of the difference in contaminating by-products in the corresponding PPP.
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