Electrochemical and optoelectronic characterization of novel poly[2,5-dialkoxy-p-phenyleneethynylene-2,7-(9,9-fluorene)]s with 7-oxy-4-methylcoumarin side groups

Two new poly[2,5-dialkoxy-p-phenyleneethynylene-2,7-(9,9-dihexylfluorene)]s (PPEF) consisting of conjugated emitting chromophores of the backbone and pendant hexyloxy groups (P1) or pendant 7-oxygen-4-methylcoumarin (OMC) chromophores via flexible spacer (P2), have been successfully prepared and their electrochemical and optoelectronic properties are investigated. The emission of P2 in solution is similar to model polymer (P1), and they show peak at 445 nm, which is attributed to PPEF backbone. Accordingly, efficient energy transfer from the OMC chromophores to PPEF backbone occurred readily in P2. The HOMO and LUMO energy levels of the two polymers have been estimated from their cyclic voltammograms. All the observations directly prove that the oxidation starts at the hole transporting segments of main chain. The electron affinity can be enhanced by introducing isolated electron-transporting side groups that lead to charges injection balance. The double layer polymer light-emitting diodes (PLED) of ITO/PEDOT:PSS /P1-P2/Ca:Al are fabricated, and they both emit yellow color light in electroluminescence (EL) spectra. Moreover, incorporation of OMC unit increases the electron affinity and reduces the turn-on electric field.