Fluorene-thiophenes

An increase in the PL QE of the fluorene-thiophene copolymers can be achieved by introduction of -oxidized thiophene units (although no efficient EL from such materials was reported). This aspect and the chemical structures of thiophene-iS,5 -dioxide-fluorene copolymers are discussed in more detail in Section 2.4. 

B. Liu, W.-L. Yu, Y.-H. Lai, and W. Huang, Synthesis, characterization, and structure-property relationship of novel fluorene-thiophene-based conjugated copolymers, Macromolecules, 33 8945-8952, 2000. 

S. Destri, M. Pasini, W. Porzio, G. Gigi, D. Pisignano, and C. Capolupo, Emission properties and solid-state aggregation in poly(fluorene-thiophene-5,5-dioxide) and in its model oligomer, Synth. Met., 138 289-293, 2003. 

Beaupre and Leclerc reported fluorene-thiophene copolymers in which fluorene and thiophene-S,S-dioxide fragments 558 and 559 were separated by one or two thiophene units (02MI192). 

Vamvounis and Holdcroft prepared a series of fluorene-thiophene copolymers 579 with a varying ratio of conjugated (2,5-thienylene) and nonconjugated (3,4-thienylene) thiophene moieties in the polymer chain (04AM716). The PL efficiencies in films are low (6 and 7%, respectively). Substantial increases in solid-state PL efficiencies were observed reaching a value of 43% for copolymer 579e. 

Fluorene-thiophene-phenylene copolymers 592-593 clearly demonstrate the effect of the exact position of CN groups in the vinylene fragment on the emission of the materials (04MM5265). 

Ravirajan P., Haque S. A., Durrant J. R., Poplavskyy D., Bradley D. D. C. and Nelson J. (2004), Hybrid nanocrystalline TiOi solar cells with a fluorene-thiophene copolymer as a sensitizer and hole conductor , J. Appl. Phys. 95, 1473-1480. 

Finally, conjugated materials 40 based on poly(phenylene thiophene) and poly (fluorene thiophene) main chain polymers functionalized with pendant trithiocyanato ruthenium terpyridine complexes were synthesized by the Suzuki coupling reaction. Heterojunction photovoltaic cells with the simple structure ITO/polymer/C-60/Al were fabricated. Under simulated AM1.5 solar light illumination, the short circuit currents, open circuit voltages, and power conversion efficiencies of the photovoltaic cells were measured to be 1.53-2.58 mAcm 2, 0.12-0.24 V, and 0.084-0.12%, respectively [77]. 

Pattison, L.R. et ah. Temperature dependence of the ordering of semiconducting fluorene-thiophene copolymers on rubbed polyimide alignment layers, in Organic photovoltaics VI, ed. Z.H. Kafafi and P.A. Lane, SPIE, Bellingham, WA, 2005, 143-150. 

Polyfluorenes are an important class of LEP with high thermal, photo and environmental stability and efficient bright blue emission. This stimulated a number of researchers to develop fluorene-thiophene copolymers for light-emitting applications. In addition to an expected increase in PL quantum etSciency, such a combination of electron-rich thiophene units with relatively electron-deficient fluorene units should modify the bandgap of the material (and thus tune the emission) and improve the charge injection/transport balance, compared with fluorene homopolymers. 

Huang s group has systematically studied the structure-property relationships of fluorene-thiophene-based conjugated polymers 57-60 [95, 96], In contrast to poly thiophene homopolymers, the regiochemistry of substitution in bithiophene fragments in the studied copolymers shows little effect on the optical bandgap (59 and 60, respectively Eg = 2.49 and 2.58 eV [96] or 2.57 and 2.60 eV [97, 98]) or the emission maxima, but the head-to-head copolymer 60 was significantly more thermally stable. 

Scheme 19.6 Synthesis of fluorene-thiophene copolymers 64a-fand the effect of the ratio of thienylene isomers in the copolymers on the PL efficiency. Numbers in the abbreviations of copolymers denote the portion of A in the mixture of A-E B...

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