(9,9-Dialkylfluorene-co-fluorenone) copolymers containing low fluorenone fractions as model systems for degradation-induced changes in polyfluorene-type semiconducting materials

Abstract

This short communication describes synthesis, optical and electronic properties of novel 9,9-dialkylfluorene-co-fluorenone copolymers which function as model systems for degradation-induced changes in polyfluorene-type semiconducting materials. Only very small fractions of incorporated fluorenone building blocks lead to a dramatic change of the solid state properties (photo-and electroluminescence). The results are discussed in terms of intra-vs. intermolecular excitation energy transfer.

Decoupling 2D Inter‐ and Intrachain Energy Transfer in Conjugated Polymers

“…[18,25] However, rapid oxidation of the poly(9,9-di-n-hexylfluorene) to the green-emitting keto defect (fluorenone) [21,24,25] and the high spectral overlap between PF emission and fluorenone absorption lead to suppression of the desirable blue emission and generate an undesirable green emission. [19,20,22,[26][27][28][29][30][31][32] This color shift from blue to green is also observed in polyfluorene light-emitting diodes on driving current through the device, and thus limits the potential of PF for application in the blue spectral region. [18,21,33] The efficient PF-fluorenone energy transfer is evident from the absorption (Figure 1 A) and emission spectra (Figure 1 B) of a pristine PF film and films of PF with 1, 2, or 5 mol % of the fluorenone defects.…”

“…General Polymerization Procedure: The 2,7-dibromo-9,9-di-n-octyl-9H-fluorene and 2,7-dibromo-9-fluorenone monomers were synthesized according to literature procedures. [9,[18][19][20][21][22][23][24] A mixture of 2,7-dibromo-9,9-di-n-octyl-9H-fluorene (500 mg, 0.91 mmol), the required amount of 2,7-dibromo-9-fluorenone, 2,2'-dipyridyl (314 mg, 2.01 mmol), COD (218 mg, 2.01 mmol), [NiA C H T U N G T R E N N U N G (COD) 2 ] (602 mg, 2.19 mmol), and THF (25 mL) was stirred at 80 8C under argon for 72 h. The end-capper 1-bromobenzene (0.1 equiv) was added dropwise to terminate the polymerization reaction. The mixture was poured into CHCl 3 (50 mL) and extracted with HCl (50 mL), Na/ ethylenediaminetetraacetic acid (50 mL), NaHCO 3 (50 mL), and H 2 O (50 mL).…”

The Origin of Green Emission in Polyfluorene‐Based Conjugated Polymers: On‐Chain Defect Fluorescence

“…[11] In order to ensure that these copolymers are valid model systems for degraded polyfluorene, we have undertaken extensive degradation studies of pristine polyfluorene. The most important results are summarized in Figure 1, where the photoluminescence spectrum of a pristine polyfluorene film is shown together with the spectra of The low emission band at 2.2±2.3 eV in polyfluorene-based conjugated materials is studied by various spectroscopic methods on defined copolymers of 9±9¢-difarnesyl-fluorene with 9-fluorenone, which can be seen as a model compound for degraded polyfluorenes.…”

The Influence of UV Irradiation on Ketonic Defect Emission in Fluorene‐Based Copolymers

“…[20]. The polymers were dissolved in toluene and chloroform, respectively, spin coated onto quartz substrates and heated at 90 8C for at least 2 hours for solvent evaporation with slow temperature up and down ramps.…”