Poly thiophenes represent an important class of electrochromic materials due to their intense color changes, robust environmental and redox stabilities, and facile structural modifications.
Soluble poly thiophenes have been prepared by substituting the 3- or 4-, or both 3- and 4- positions of the thiophene ring with flexible units, such as alkyl, alkoxy, or alkylenedioxy units [ 12 ].
Thiophenes and their derivatives are also frequently used as the donor units for the preparation of D-A-type polymers with the acceptor units electron-deficient units [ 12 ]. In addition, as redox-active chromophores, the alkyl-substituted carbazole and fluorene has been used as the donor units for the construction of D-A-type polymeric electrochromic materials, which usually present multichromic properties, depending on the selection of the constitutional units [ 14 , 15 , 16 ].
Meanwhile, the formation of interchain Se—Se interactions could also be anticipated and be attributed to the better polarizability of the Se atom compared to the sulfur atom, which leads to the higher charge carrier mobility of the Se-containing polymers [ 17 , 18 , 19 ].
Selenophene and benzoselenadiazole BSe are two common heteroaromatic compounds and carriers of Se atoms, which are used as electron-donating and electron-deficient building blocks, respectively, for the preparation of D-A-type conjugated polymers [ 17 , 18 , 19 ].
Besides the BSe unit, its derivatives including 4,7-dibromo-5,6-bis octyloxy -[2,1,3]-benzoselenadiazole BSeoc or 4,7-bis 5-bromothiopheneyl -5,6-bis octyloxy -[2,1,3]-benzoselenadiazole DTBSe have also been employed as electron-accepting units [ 17 ], and the introduction of the alkoxy units was considered to be able to increase the solubility of the resultant polymers.
Hyun reported that the replacement of thiophene with selenophene in the BSeoc-containing polymers led to the lower bandgap and higher photovoltaic performance compared to its thiophene-containing analogues [ 8 ]. BSe- or selenophene-containing conjugated polymers were also prepared and characterized in terms of their electrochromic properties, which usually showed lower bandgaps and higher redox stabilities than that of their analogues [ 4 , 24 ].
A soluble copolymer consisting of BSe and 2,5-bis-dithienyl-1H-pyrrole has been synthesized by Koyuncu et al. To date, the reports on soluble BSe-containing electrochromic polymers are few, which should be further extended and strengthened due to the good application records of BSe and its derivatives in the field of organic photovoltaics OPVs [ 25 ].
In this report, we prepared six conjugated polymers with 4,7-bis 5-bromohexythiophenyl benzo[c][1,2,5]selenadiazole 2Br-HT-BSe , 4,7-bis 5-bromo-3,4-bis hexyloxy thiopheneyl benzo[c][1,2,5]selenadiazole 2Br-HoT-BSe , and 4,7-bis 5-bromo-3,4-bis octyloxy thiopheneyl benzo[c][1,2,5]selenadiazole 2Br-OoT-BSe as the electron accepting units, and 9- octylnonylyl -2,7-bis 4,4,5,5-tetramethyl-1,3,2-dioxaborolanyl -9H-carbazole BAcarb or 2,7-bis 4,4,5,5-tetramethyl-1,3,2-dioxaborolanyl -9,9-dioctylfluorene BAfluo as the electron-donating units.
The structures of the above three acceptor units and six alternating copolymers are shown in Scheme 1 and Scheme 2. The effects of the side-chain substituent located on the thiophene ring and the electron-donating units on the electrochromic properties of the resultant polymers are summarized and discussed in detail. Experimental Section 2. Materials 4,7-dibromo-2,1,3-benzoselenadiazole BSe , 3-hexylthiophene, 3,4-dihexyloxythiophene, and 3,4-dioctyloxythiophene were all purchased from Puyang Huicheng Electronic Material Co.
The 2-substituted tributylstannane derivatives of the thiophene derivatives were prepared with the methods reported previously [ 25 ]. Shenzhen, China and used without further purification. SCE as the pseudo-reference electrode. The supporting electrolyte used for all electrochemical measurements was 0.
The three-electrode system was constructed on a quartz cell, with the polymer-coated ITO electrode as the working electrode WE electrode, and the Pt and Ag wires were used as the counter and reference electrodes, respectively. The chromatic coordinates of the polymers under different potentials were measured with the same apparatus as used in the spectroelectrochemical measurement with the employment of the chromaticity software Varian Inc.
Prior to each set of measurements, background color coordinates x, y, and z values were taken at open-circuit, using the electrolyte solution without the polymer films under study. Digital photographs of the polymer films were taken by a Canon Canon Inc. Manna, and Apurba K. Chemistry of Materials , 27 19 , Kobilka, and Benjamin J. Macromolecules , 47 21 , Lin, and Kung-Hwa Wei.
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Chapman, Neil J. Findlay, Peter J. Skabara, Peter N. Horton, Simon J. Investigating the effect of heteroatom substitution in 2,1,3-benzoxadiazole and 2,1,3-benzothiadiazole compounds for organic photovoltaics. Journal of Materials Chemistry C , 6 14 , Cyano-substituted benzochalcogenadiazole-based polymer semiconductors for balanced ambipolar organic thin-film transistors. Polymer Chemistry , 9 28 , Chemistry Letters , 46 8 , Itaru Osaka, Kazuo Takimiya.
Advanced Materials , 29 25 , Polymers , 9 7 , Chemical Physics Letters , , Metal carbonyl complexes of potentially ambidentate 2,1,3-benzothiadiazole and 2,1,3-benzoselenadiazole acceptors. Can time-dependent density functional theory predict intersystem crossing in organic chromophores? A case study on benzo bis -X-diazole based donor—acceptor—donor type molecules.
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Selenium and Tellurium Containing Conjugated Polymers. Meanwhile, the formation of interchain Se—Se interactions could also be anticipated and be attributed to the better polarizability of the Se atom compared to the sulfur atom, which leads to the higher charge carrier mobility of the Se-containing polymers [ 17 , 18 , 19 ].
Compared with inorganic electrochromic compounds, such as WO3 and IrO2, soluble polymeric electrochromic materials have some merits, including the ease of the fabrication of large films, bright colors, large optical contrast ratios, and fast response speeds [ 12 ]. The organic phase was extracted with chloroform and was combined together after two rinsing processes. Chemical Reviews , 12 , Kuklin, D. The alternating distribution of one donor unit and one acceptor unit along a polymer backbone is the basic feature of the donor-acceptor D-A theory, which is considered to be the most effective way to reduce the bandgaps of polymers, by promoting intramolecular charge transfers and then improving the resonance effects on the polymer backbone [ 4 , 5 ]. RSC Advances , 6 89 ,
A soluble copolymer consisting of BSe and 2,5-bis-dithienyl-1H-pyrrole has been synthesized by Koyuncu et al. Keywords: benzoselenadiazole, carbazole, fluorene, conjugated polymer, electrochromic, solution processable 1. Advanced Materials , 29 25 , It is considered that bandgap values are the results of many factors, including planarity, resonance effects, interchain effects, and bond length alternation [ 3 ]. Poly thiophenes represent an important class of electrochromic materials due to their intense color changes, robust environmental and redox stabilities, and facile structural modifications.
Chemical Reviews , 12 , Journal of Materials Chemistry C , 4 34 ,
Dana D. Chemical Physics Letters , , Macromolecules , 47 20 , Horton, Simon J. Ahipa, Ranjith Krishna Pai.
Before the flask was filled with argon gas, the air in the flask was pumped out by a vacuum pump. Manna, and Apurba K. The selection of the donor units between the carbazole and the fluorene units has nearly no effect on the bandgaps and colors as well as the onset oxidation potentials of the polymers. Macromolecules , 47 21 , SCE as the pseudo-reference electrode.