Poly(2,7-phenanthrylene)s and poly(3,6-phenanthrylene)s as polyphenylene and poly(phenylenevinylene) analogues

Abstract

The synthesis of a series of soluble poly(2,7-phenanthrylene)s and poly(3,6-phenanthrylene)s is presented. Depending on the nature of the repeat units they constitute analogues of poly(p-phenylene) (PPP) and poly(p-phenylenevinylene) (PPV) and thus should give rise to different modes of extended π-conjugation. In the case of the 9,10-dialkyl-substituted poly(2,7-phenanthrylene) and poly(3,6-phenanthrylene), spectroscopic characterization suggests polymer aggregation in the solid state, which can be efficiently suppressed by the introduction of aryl substituents to result in a narrow blue emission. The 2,7- or 3,6-coupling of the phenanthrenes has a strong influence on the emission properties of the polymers. The PPP analogue shows less vibronic coupling in emission due to the rigid-rod nature of the polymer as compared to the PPV analogue. Moreover, the photoinduced absorption features of the 2,7-linked derivatives are similar to PPP-type polymers, whereas the 3,6-linked derivatives exhibit a behavior typically found in PPV-type polymers. In the solid state, the PPV analogues show a more pronounced red-shift of the emission, which is assigned to the solid-state packing of the polymers. The polymers display deep blue electroluminescence and good color stability when tested in a polymer light emitting device. The formation of long wavelength emission bands, typically attributed to keto defects, is not observed. Additionally, 2,7- and 3,6-linked tris(phenanthrylene)s are synthesized as model compounds and their optical properties discussed in comparison with their polymer analogues.