CONTRIBUTIONS OF NONCONJUGATED SPACERS TO PROPERTIES OF ELECTROLUMINESCENT BLOCK-COPOLYMERS

Six electro-optically active alternating block copolymers consisting o f short substituted phenylene vinylene sequences interspersed with opt ically inert oligomethylene blocks were synthesized using a Wittig con densation scheme. In this study, the focus was on the effect of the al iphatic spacer length, which was systematically varied from two to twe lve methylene units. The copolymers were soluble in standard organic r eagents and were characterized by NMR, FTIR, elemental analysis, GPC, UV-vis, and DSC. The vinylene groups in the conjugated blocks were iso merized into the all-trans form by refluxing in toluene with catalytic iodine. The electroluminescent spectra of the six copolymers were sim ilar and displayed a maximum around 465 nm. The EL efficiency of the s ingle-layer LEDs fabricated with the copolymer chromophores was a func tion of the length of the nonconjugated spacer blocks; copolymers with longer spacers yielded higher-efficiency devices.