Photophysical and electroluminescent properties of fluorene-based binary and ternary donor-acceptor polymer blends

The photophysical and electroluminescent properties of fluorene-based polymer blend systems were studied, including blue-emitting poly[2,7-(9,9'-dihexylfluorene)] (PF), green-emitting poly[2,7-(9,9'-dihexylfluorene)-alt-5,8-quinoxaline] (PFQ), yellow-emitting poly[2,7-(9,9'-dihexylfluorene)-alt-4,7-(2,1,3-benzothiadiazole)I (PFBT), and red-emitting poly[2,7-(9,9'-dihexylfluorene)-alt-5,7-(thieno[3,4-blpyrazine)] (PFTP). The binary polymer blends, based on PF blended with 5-25 wt % PFQ or PFBT, were studied to rationalize the effects of the chemical structures and compositions on the intermolecular energy transfer and quantum efficiency. A significant enhancement of quantum efficiency was observed by the blending of a relatively small amount of PFQ or PFBT. Ternary blends composed of PIT, PFQ (or PFBT), and PFTP were also studied for potential white-light-emitting diodes (WLEDs). The precise composition control of the polymer blends resulted in incomplete Forster energy transfer and emissions from all the components simultaneously. White-emitting electroluminescence was achieved by the blending of PF with relatively small amounts of the PFQ (or PFBT) and PFTR The luminance yield and maximum external quantum efficiency of the WLED with the ternary blend FBTTP1 (PF/PFBT/PFTP = 99.65:0.05:0.30 w/w/w) as the emissive layer were 1.89 cd/A and 0.47%, respectively. The electron-acceptor characteristics, Forster energy transfer, and emissive colors govern the design of WLEDs. (c) 2006 Wiley Periodicals, Inc.