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Title: Altering the Polymorphic Accessibility of Polycyclic Aromatic Hydrocarbons with Fluorination

Here, substituting hydrogen with fluorine is an extensively employed strategy to improve the macroscopic properties of compounds for use in fields as diverse as pharmaceutics and optoelectronics. The role fluorine substitution plays on polymorphism—the ability of a compound to adopt more than one crystal structure—has not been previously studied. Yet, this understanding is important as different polymorphs of the same compound can result in drastically different bulk properties (e.g., solubility, absorptivity, and conductivity). Strategies to either promote or suppress the crystallization of particular polymorphs are thus desired. Here, we show that substituting hydrogen with fluorine affects the polymorphic behavior of contorted hexabenzocoronene (cHBC). A polycyclic aromatic hydrocarbon and molecular semiconductor, cHBC exhibits two polymorphs (i.e., P2 1/c crystal structure which we refer to as polymorph I and a triclinic crystal structure which we refer to as polymorph II) that are accessible through postdeposition processing of amorphous films. While the same two polymorphs remain accessible in fluorinated derivatives of cHBC, fluorination appears to favor the formation of polymorph I, with progressively smaller energy barrier for transformation from polymorph II to polymorph I with fluorination.
Authors:
 [1] ;  [2] ;  [3] ; ORCiD logo [4] ; ORCiD logo [5]
  1. Princeton Univ., Princeton, NJ (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Cornell Univ., Ithaca, NY (United States)
  3. Columbia Univ., New York, NY (United States); New Jersey City Univ., Jersey City, NJ (United States)
  4. Columbia Univ., New York, NY (United States)
  5. Princeton Univ., Princeton, NJ (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-713258
Journal ID: ISSN 0897-4756; TRN: US1702851
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 10; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1399740