title: Understanding polymorphism in organic semiconductor thin films through nanoconfinement.
abstract: Understanding crystal polymorphism is a long-standing challenge relevant to many fields, such as pharmaceuticals, organic semiconductors, pigments, food, and explosives. Controlling polymorphism of organic semiconductors (OSCs) in thin films is particularly important given that such films form the active layer in most organic electronics devices and that dramatic changes in the electronic properties can be induced even by small changes in the molecular packing. However, there are very few polymorphic OSCs for which the structure-property relationships have been elucidated so far. The major challenges lie in the transient nature of metastable forms and the preparation of phase-pure, highly crystalline thin films for resolving the crystal structures and evaluating the charge transport properties. Here we demonstrate that the nanoconfinement effect combined with the flow-enhanced crystal engineering technique is a powerful and likely material-agnostic method to identify existing polymorphs in OSC materials and to prepare the individual pure forms in thin films at ambient conditions. With this method we prepared high quality crystal polymorphs and resolved crystal structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), including a new polymorph discovered via in situ grazing incidence X-ray diffraction and confirmed by molecular mechanic simulations. We further correlated molecular packing with charge transport properties using quantum chemical calculations and charge carrier mobility measurements. In addition, we applied our methodology to a [1]benzothieno[3,2-b][1]1benzothiophene (BTBT) derivative and successfully stabilized its metastable form.
authors.affiliation: Department of Chemical Engineering, Stanford University , Stanford, California 94305, United States.
authors.forename: Ying
authors.initials: Y
authors.lastname: Diao
authors.forename: Kristina M
authors.initials: KM
authors.lastname: Lenn
authors.forename: Wen-Ya
authors.initials: WY
authors.lastname: Lee
authors.forename: Martin A
authors.initials: MA
authors.lastname: Blood-Forsythe
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.forename: Yisha
authors.initials: Y
authors.lastname: Mao
authors.forename: Yeongin
authors.initials: Y
authors.lastname: Kim
authors.forename: Julia A
authors.initials: JA
authors.lastname: Reinspach
authors.forename: Steve
authors.initials: S
authors.lastname: Park
authors.forename: Alán
authors.initials: A
authors.lastname: Aspuru-Guzik
authors.forename: Gi
authors.initials: G
authors.lastname: Xue
authors.forename: Paulette
authors.initials: P
authors.lastname: Clancy
authors.forename: Zhenan
authors.initials: Z
authors.lastname: Bao
authors.forename: Stefan C B
authors.initials: SC
authors.lastname: Mannsfeld