title: Dependence of Excited-State Properties of a Low-Bandgap Photovoltaic Copolymer on Side-Chain Substitution and Solvent.
abstract: The excited-state properties and chain conformations of a new low-bandgap copolymer based on benzo[1,2-b:4,5-b']dithiophene (BDT) and thieno[3,4-b]thiophene with meta-alkoxyphenyl-substituted side chains in solution were investigated comprehensively. Time-resolved spectroscopy suggested that the excited-state properties were sensitive to the conformations of the copolymer in solution. In addition, excited-state dynamics analyses revealed the photogeneration of triplet excited states by intersystem crossing (ISC) at a rate constant of ∼0.4×10(9)  s(-1) as a result of direct meta-alkoxyphenyl connection to the donor unit BDT irrespective to the macromolecular conformations. According to El-Sayed's rule, the fast ISC herein is correlated with the change of orbital types between singlet and triplet excited states as also shown by quantum chemical calculations. Our studies may shed light on the structure-property relationships of photovoltaic materials.
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Ning-Jiu
authors.initials: NJ
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Science, Beijing, 100190, P.R. China.
authors.forename: Mao-Jie
authors.initials: MJ
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Ran
authors.initials: R
authors.lastname: Liang
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Li-Min
authors.initials: LM
authors.lastname: Fu
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Xi-Cheng
authors.initials: XC
authors.lastname: Ai
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Science, Beijing, 100190, P.R. China.
authors.forename: Jian-Hui
authors.initials: JH
authors.lastname: Hou
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China. jpzhang@chem.ruc.edu.cn.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
mesh_terms: D011211:Electric Power Supplies; D007700:Kinetics; D008968:Molecular Conformation; D055668:Photochemical Processes; D011108:Polymers / Q000737:chemistry*; D012993:Solar Energy; D012997:Solvents / Q000737:chemistry*; D013876:Thiophenes / Q000737:chemistry; D014050:Toluene / Q000737:chemistry
chemical_list: D011108:Polymers; D012997:Solvents; D013876:Thiophenes; D014050:Toluene
keywords: electron transfer; polymers; solar cells; structure-activity relationships; substituent effects