Synthesis and characterization of light-emitting oligo(p-phenylene-vinylene)s and polymeric derivatives containing three- and five-conjugated phenylene rings

Abstract

Several series of light-emitting oligo(p-phenylene-vinylene)s (BIII and BV series containing three- and five-conjugated phenylene rings) with various side groups and end groups attached to the cores were synthesized and characterized. The analogous PBV polymers, derived from the BV series, were also synthesized and investigated. Blue and greenish light emissions were observed in the photoluminescence (PL) and electroluminescence (EL) spectra of the blend and pure films with these pi-conjugated structures. In contrast to the three-conjugated ring oligomers, the five-conjugated ring derivatives (oligomers and polymers) had larger maximum emission wavelength values of PL and EL emissions. Mesomorphism was introduced into the BV series by the replacement of three-conjugated rings (BIII series) with five-conjugated phenyl cores (BV series). The liquid-crystalline properties of the BV series with end groups (on both end rings) were better than those of analogous BV-OC8 without end groups. Polarized PL emissions were obtained by the alignment of liquid-crystalline phase in rubbing cells. Upon heating, different PL emission wavelengths and intensities were observed in various phases. Not only the solubility and thermal properties but also the PL and EL properties could be effectively adjusted by the attachment of flexible alkoxy groups either on the central rings or on both end rings of the conjugated cores. (c) 2005 Wiley Periodicals, Inc.