Electron-deficient asymmetrically substituted diarylindenotetracenes were prepared via a series of Friedel-Crafts acylations, aryl-aryl cross-couplings, and an intramolecular oxidative cyclization to form the indene ring. Single-crystal X-ray experiments showed good π-π overlap with π-π distances ranging from 3.26 to 3.76 Å. Both thermogravimetric analysis and differential scanning calorimetry indicated that asymmetrically substituted indenotetracenes (ASIs) are stable at elevated temperatures. From cyclic voltammetry experiments, HOMO/LUMO energy levels of ASI derivatives were determined to be near -5.4/-4.0 eV. UV/visible absorption spectra showed strong absorption of light between 400 and 650 nm with molar attenuation coefficients from 104 to 105 M-1 cm-1. ASIs were also found to have very low fluorescence quantum yields, less than 4%. Using the solid-state packing determined from the single-crystal X-ray experiments, computational modeling indicated that ASI molecules should favor electron transport.
Bibliographical noteFunding Information:
This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program, and the Office of Advanced Scientific Computing Research through the Scientific Discovery through Advanced Computing (SciDAC) program under Award Number DE-SC0008666. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract number DESC0014664. The National Science Foundation is acknowledged for support via the MRSEC program (DMR-1006566) and for a grant to purchase the Bruker-AXS D8 Venture single-crystal diffractometer (MRI-1229400), along with the University of Minnesota. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper, and Professor Laura Gagliardi (UMN) for helpful discussions. C.J.D. thanks DuPont for a Young Professor Award.