Three homopolymers (PFICY, PF4CY, and PF7CY) and two random copolymers (PFI CYEH41 and PFICYEH11), which have only fluorene units in the backbone, were synthesized by Ni(0)-mediated polymerization to lessen the excimer formation often observed in polyfluorenes.
All the homopolymers showed high thermal stability, and except PFICY, PF4CY and PF7CY were highly soluble towards common organic solvents. EL devices of a configuration ITO/PEDOT/polymer/LiF/Al were fabricated. PF4CY displayed green electroluminescence of an excimer emission with the maximum at 540 nm. However, PF7CY``s EL spectrum showed pure blue light emission with the maximum emission at 433 nm with suppressed excimer formation. The CIE (Commision Internationale de I``Eclairage) coordinates of such emission were determined to be (0.18, 0.13) which makes PF7CY a promising blue-light-emitting polymer.
The solubility of the PFICYEH random copolymers was very much improved compared with the PFICY homopolymer. In addition, there was a significant increase in the glass-transition temperatures with the copolymers. Because of their high glass-transition temperatures, excimer emission was barely seen after thermal annealing. The PFICYEH random copolymers also showed pure blue light emission from the ITO/PEDOT/polymer/LiF/Al configuration EL devices with their maximum emission peaks at 425 nm. These polymers are also expected to be a good candidate as a bluelight-emitting polymer with their exceptionally high thermal stability as a polyfluorene.