Fluorene-benzothiadiazole copolymers

Q. Hou, Q. Zhou, Y. Zhang, W. Yang, R. Yang, and Y. Cao, Synthesis and electroluminescent properties of high-efficiency saturated red emitter based on copolymers from fluorene and 4,7-di(4-hexylthien- 2-yl)-2,l,3-benzothiadiazole, Macromolecules, 37 6299-6305, 2004. 

P. Herguth, X. Jiang, M.S. Liu, and A.K.-Y. Jen, Highly efficient fluorene and benzothiadiazole-based conjugated copolymers for polymer light-emitting diodes, Macromolecules, 35 6094-6100, 2002. 

Copolymers 15 (Fig. 6) derived from 2,7-fluorene and 2,5-dithienylsilole show red fluorescence via an energy transfer process.31 The APl could be 591 nm for copolymers with higher contents of 2,5-dithienylsilole. The absolute PL quantum yields (<30%) of the copolymers are somewhat lower than the green fluorescent SCPs. A copolymer 16 derived from 2,7-dibenzosilole and 4,7-dithienyl-2,l,3-benzothiadiazole show a better red fluorescence.26 The APL of the copolymer is at 629 nm, with an absolute PL quantum yield of 53%. 

Green electroluminescence is also achieved from the well-defined alternating copolymer 12 with a repeating unit made up of ter-(2,7-fluorene) and 2, 5-silole.29 With its neat film as the emissive layer, the EL device shows a maximum //Kr of 0.47%, but the device performance can be largely improved to a maximum //Ki. of 1.99% when using a copolymer/PF8 blend film as the emissive layer. Copolymer 14 derived from 2,7-dibenzosilole and 2,1,3-benzothiadiazole is also an excellent green EL polymer.26 A maximum 7el of 3.81% can be realized in EL devices. 

A low band gap copolymer consists of poly(2,7-(9,9-dioctyl)fiuorene-co-5,5 -(4,7-diselenophenyl)-2,2 -yl-2,l,3-benzothiadiazole). The optical band gap of this type of copolymer is very low, e.g., 1.87 eV for a copolymer obtained from substituted fluorene and 4,7-diselenophen-2 -yl-2,1,3-benzothiadiazole, and 1.77 eV for a similar copolymer from 4,7-dise-lenophen-2 -yl-2,l,3-benzoselenadiazole. The efficient fast energy transfer from fluorene segments to narrow band gap sites was observed. 

R. Verduzco, I. Botiz, D. L. Pickel, S. M. Kilbey, K. Hong, E. Dimasi, S. B. Darling, Polythiophene-BZocfc-Polyfluorene and Polythiophene-B/ocfc-Poly(Fluorene-co-Benzothiadiazole) Insights into the Self-Assembly of All-Conjugated Block Copolymers. Macromolecules 2011,44, 530-539. 

Andersson and coworkers have prepared solar cells based on blends of poly(2,7-(9-(2 -ethylhexyl)-9-hexyl-fluorene)-fl/t-5,5-(4, 7 -di-2-thienyl-2, l, 3 -benzothiadiazole) (223) and PCBM [416]. The polymer shows a Amax (545 nm) with a broad optical absorption in the visible spectrum and an efficiency of 2.2% has been measured under simulated solar light. The same group has also reported the synthesis of low bandgap polymers 200 (1 = 1.25 eV) and 224 (1 = 1.46 eV) which have been blended with a soluble pyrazolino[70]fiillerene and PCBM, respectively, to form bulk heterojunction solar cells of PCE of 0.7% [417] and 0.9% [418]. Incorporation of an electron-delident silole moiety in a polyfluorene chain affords an alternating conjugated copolymer (225) with an optical bandgap of 2.08 eV. A solar cell based on a mixture 1 4 of 225 and PCBM exhibits 2.01% of PCE [419]. 

Other thiophene-based donor-acceptor-type copolymers that have shown efficiencies of over 4.2% include poly (fluorene-dicyclopentathiophene-a/t-benzothiadiazole) (65, Figure 25), poly(carbazole-dicyclopentathiophene-aft-benzothiadiazole) 66, and poly[9,9-dialkylfluorene-a/t-(bis-thienylene)benzothiadiazole] 67-69. Some other thiophene-based polymer designs, which have attracted... 

Verduzco, R. Botiz, I. Pickel, D. L. Kilbey II, S. M. Hong, K. Dimasi, E. and Darling, S. B., Polythiophene-block-polyfluorene and polythiophene-block-poly(fluorene-co-benzothiadiazole) Insights into the self-assembly of all-conjugated block copolymers. Macromolecules, 44,530-539 (2011) DOI 10.1021/ mal02728z. 

---