title: Theoretical study of substitution effects on molecular reorganization energy in organic semiconductors.
abstract: Chemical substitutions are powerful molecular design tools to enhance the performance of organic semiconductors, for instance, to improve solubility, intermolecular stacking, or film quality. However, at the microscopic level, substitutions in general tend to increase the molecular reorganization energy and thus decrease the intrinsic charge-carrier mobility. Through density functional theory calculations, we elucidate strategies that could be followed to reduce the reorganization energy upon chemical substitution. Specific examples are given here for hole-transport materials including indolo-carbazoles and several triarylamine derivatives. Through decomposition of the total reorganization energy into the internal coordinate space, we are able to identify the molecular segment that provides the most important contributions to the reorganization energy. It is found that when substitution reduces (enhances) the amplitude of the relevant frontier molecular orbital in that segment, the total reorganization energy decreases (increases). In particular, chlorination at appropriate positions can significantly reduce the reorganization energy. Several other substituents are shown to play a similar role, to a greater or lesser extent.
authors.affiliation: Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Geng
authors.forename: Yingli
authors.initials: Y
authors.lastname: Niu
authors.forename: Qian
authors.initials: Q
authors.lastname: Peng
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Shuai
authors.forename: Veaceslav
authors.initials: V
authors.lastname: Coropceanu
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Brédas
mesh_terms: D000588:Amines / Q000737:chemistry*; D002227:Carbazoles / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory; D012666:Semiconductors; D013237:Stereoisomerism
chemical_list: D000588:Amines; D002227:Carbazoles