Light Emission Properties of a Cross-Conjugated Fluorene Polymer: Demonstration of Its Use in Electro-Luminescence and Lasing Devices

摘要

Light emission properties of a fluorene cross-conjugated polymer ( PF–1 ) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence quantum yield of approximately 1. Based on these features, in this paper we implemented the use of PF–1 as an active layer in polymer light-emitting diodes (PLEDs) and as a laser gain medium in solution. To get insight on the conducting properties of PF–1 , two different electron injectors, poly [(9,9-bis(3′-( N , N -dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] ( PFN ) and lithium fluoride ( LiF ), were used in a simple PLED architecture. PLEDs with the PFN film were found to exhibit better performance with a maximum luminous efficiency of 40 cd/A, a turn-on voltage ( V on ) of approximately 4.5 V and a luminance maximum of 878 cd/m 2 at 5.5 V, with a current density of 20 A/m 2 . For the lasing properties of PF–1 , we found a lasing threshold of around 75 μJ and a tunability of 20 nm. These values are comparable with those of rhodamine 6G, a well-known laser dye.