Tuning of redox behavior and fluorescence of cyano-containing oligophenylenevinylenes

A series of cyano-containing distyrylbenzenes which have the electron-withdrawing groups functionalized on the central phenylene ring were synthesized via the Wittig-Horner reaction. Electrochemical study showed that the electron-affinity of these molecules increased with the increasing strength of electron-accepting groups. 1,4-Bis(4′t-Butylstyryl)-2,5-bis(dicyanovinyl)benzene possessed a low LUMO energy level at -4.01 eV, which provided a better match to the work function of Al cathode. Compared to the cyano-terephthalylidene, introducing cyano groups on the aromatic ring instead of on the vinylene linkage provided better stabilization to the radical anions. The emission colors spanning green, yellow, orange, red could be achieved by changing the electron-accepting strength of oligophenylenevinylenes. Energy gap reductions were caused by a stronger decrease of the LUMO energies than the HOMO energies. These results provided new insights for the design of suitable polymers with much improved electron affinities facilitating electron injection from higher work function metal electrodes.