Spectroscopic and electrochemical study of a novel blue electroluminescentp-n diblock conjugated copolymer

A novel p-n diblock copolymer, poly[N-(2'-ethylhexyl)-carbazole-3,6-diyl-1 ",3 ",4 "-oxadiazole-2 ",5 "-diyl-2''',5'''-dioctyloxy-1''', 4'''phenylene- 1'''',3'''',4''''-oxadiazole-2'''',5''''-diyl] (PCOPO) composed of an elect ron-rich moiety carbazole and an electron-deficient unit aromatic oxadiazol e was synthesized aiming at balancing the abilities of conducting holes and electrons. Electrochemical analyses by cyclic voltammetry indicate that PC OPO can be reversibly n-doped and irreversibly p-doped. The cathodic sweep reveals that the reduction involves two-electron process with respect to th e successive reduction of oxadiazole rings and carbazole moieties in the po lymer chain. The highest occupied molecular orbitals (HOMO) and lowest unoc cupied molecular orbitals (LUMO) energy levels of the polymer are estimated to be 5.60 and 2.66 eV from the onset of oxidation and reduction potential s, respectively. The band gap energy of the polymer estimated by the electr ochemical measurement (2.94 eV) is in good agreement with that from the opt ical method (2.82 eV). The photoluminescence (PL) of film samples shows tha t the polymer emits greenish-blue light (475 nm). The PL of solutions is co ncentration-dependent. In dilute solutions, the PL emission is from the sin glet exciton transition, whereas in the concentrated solutions, it is mainl y originated from excimers, The excimer formation is related to the incorpo ration of oxadiazole rings into the polymer backbone, which can enhance the interchain interactions. Both photophysical and electronic properties demo nstrate that the polymer may be a promising candidate material for the fabr ication of an efficient blue light-emitting device.