title: Shear-Triggered Crystallization and Light Emission of a Thermally Stable Organic Supercooled Liquid.
abstract: Thermodynamics drive crystalline organic molecules to be crystallized at temperatures below their melting point. Even though molecules can form supercooled liquids by rapid cooling, crystalline organic materials readily undergo a phase transformation to an energetically favorable crystalline phase upon subsequent heat treatment. Opposite to this general observation, here, we report molecular design of thermally stable supercooled liquid of diketopyrrolopyrrole (DPP) derivatives and their intriguing shear-triggered crystallization with dramatic optical property changes. Molten DPP8, one of the DPP derivatives, remains as stable supercooled liquid without crystallization through subsequent thermal cycles. More interestingly, under shear conditions, this supercooled liquid DPP8 transforms to its crystal phase accompanied by a 25-fold increase in photoluminescence (PL) quantum efficiency and a color change. By systematic investigation on supercooled liquid formation of crystalline DPP derivatives and their correlation with chemical structures, we reveal that the origin of this thermally stable supercooled liquid is a subtle force balance between aromatic interactions among the core units and van der Waals interactions among the aliphatic side chains acting in opposite directions. Moreover, by applying shear force to a supercooled liquid DPP8 film at different temperatures, we demonstrated direct writing of fluorescent patterns and propagating fluorescence amplification, respectively. Shear-triggered crystallization of DPP8 is further achieved even by living cell attachment and spreading, demonstrating the high sensitivity of the shear-triggered crystallization which is about 6 orders of magnitude more sensitive than typical mechanochromism observed in organic materials.
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Kyeongwoon
authors.initials: K
authors.lastname: Chung
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Min Sang
authors.initials: MS
authors.lastname: Kwon
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Brendan M
authors.initials: BM
authors.lastname: Leung
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Antek G
authors.initials: AG
authors.lastname: Wong-Foy
authors.affiliation: Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), and Department of Energy Science, Sungkyunkwan University , Suwon 440-746, Republic of Korea.
authors.forename: Min Su
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea; Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
authors.forename: Jeongyong
authors.initials: J
authors.lastname: Kim
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Takayama
authors.affiliation: Madrid Institute for Advanced Studies, IMDEA Nanoscience , Calle Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain.
authors.forename: Johannes
authors.initials: J
authors.lastname: Gierschner
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Matzger
authors.affiliation: Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States; Macromolecular Science and Engineering, Department of Materials Science and Engineering, Department of Biomedical Engineering, Department of Chemistry, Department of Chemical Engineering, Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan 48109, United States.
authors.forename: Jinsang
authors.initials: J
authors.lastname: Kim