Synthesis and Device Performance of a Highly Efficient Fluorene-Based Blue Emission Polymer Containing Bulky 9,9-Dialkylfluorene Substituents

We have prepared a series of highly efficient and pure blue-emitting polyfluorene (PF)-type polymers that contain 9,9-di(9,9-dihexylfluoren-2-yl)fluorene and 9-(9,9-dihexylfluoren-2-yl)-9-(3,4-di(2-methyl)butyloxyphenyl)fluorene units. The photoluminescence (PL) results show that the size of the side groups strongly influences the color purity and color stability because of the superior ability of large groups to prevent interchain interactions between polymer chains. In contrast to n-octyl functional groups, the PF with 9,9-(dihexylfluoren-2-yl) and 3,4-di(2-methyl)butyloxyphenyl side groups exhibits good PL characteristics as a blue-light-emitting polymer (LEP), showing highly enhanced color integrity and color stability against oxidative conditions over PFs based on 9,9-dioctylfluorene. When N⁴,N^4′-bis(4-methoxyphenyl)-N⁴,N^4′-diphenylbiphenyl-4,4′-diamine (13) is incorporated into the polymer backbone, the polymer exhibits a highly efficient electroluminescence performance with a luminous efficiency of 4.12 cd/A and Commission Internationale d’Eclairage (CIE) coordinates of (0.15, 0.15) in a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)−poly(styrenesulfonic acid) (PEDOT:PSS, 25 nm)/LEP (90−110 nm)/LiF (2 nm)/Al (1500 nm).