The syntheses of a series of oligo (phenylene vinylenes) (OPVs) were described. The extended it-chains were built up by sequences of Wittig reactions. Their electronic structures were systematically studied with absorption spectra, photo-luminescent spectra. The influences of the effective conjugation length on the performance of the light emitting devices were investigated. The syntheses of a series of oligo (phenylene vinylenes) (OPVs) were described. The extended it-chains were built up by sequences of Wittig reactions. Their electronic structures were systematically studied with absorption spectra, photo-luminescent spectra. The influences of the effective conjugation length on the performance of the light emitting devices were investigated.