The Lowest Excited States in Oligo(Phenylenevinylene)s: A Theoretical Investigation of Optical Absorption Spectra and Geometry Relaxation Phenomena

Abstract

Conjugated polymers have attracted a growing interest as active layers in light-emitting diodes; since the initial discovery by Burroughes et al. that poly(p-phenylenevinylene), PPV, could emit light in an efficient way¹, many efforts have been devoted to the design of novel devices with enhanced characteristics². Due to their ease of synthesis and processing under the form of stable thin films³ and to their remarkable luminescence properties⁴, PPV and its substituted derivatives arc among the most thoroughly investigated systems to be exploited in LED’s. With time, several strategies have been exploited to significantly improve the performances of these electro-optic devices; as a matter of fact, the internal quantum efficiency (defined as the number of photons emitted over the number of electrons injected) has evolved from an initial value around 0.01%’ to values up to 10%⁵.