A soluble cyano-substituted poly [(1,3-phenylene vinylene)-alt-(1,4-phenylene vinylene)] derivative (9) was synthesized and characterized. Comparison between 9 and its model compound (10) showed that the chromophore in 9 remained to be well defined as a result of a pi-conjugation interruption at adjacent m-phenylene units. The attachment of a cyano substituent only at the beta position of the vinylene allowed the maximum electronic impact of the cyano group on the optical properties of the poly(p-phenylene vinylene) material. At a low temperature (-108 or -198 degreesC), the vibronic structures of 9 and 10 were partially resolved. The absorption and emission spectra of a film of 9 were less temperature-dependent than those of a film of 10, indicating that the former had a lower tendency to aggregate. A light-emitting diode (LED) based on 9 emitted yellow light (lambda(max) approximate to 578 nm) with an external quantum efficiency of 0.03%. (C) 2003 Wiley Periodicals, Inc.