Evaluating the impact of fluorination on the electro-optical properties of cross-conjugated benzobisoxazoles

Published as part of The Journal of Physical Chemistry virtual special issue “William M. Jackson Festschrift”.Six 2,4,6,8-tetrarylbenzo[1,2-d:4,5-d′]bisoxazoles (BBOs) were synthesized: three bearing phenyl substituents at the 2- and 6-positions and three bearing perfluorophenyl groups at those positions. The influence of perfluoro-aryl group substitution on the physical, optical, and electronic properties of 2,4,6,8-tetrarylbenzo[1,2-d:4,5-d′]bisoxazoles (BBO) was evaluated using both experimental and theoretical methods. The density functional theory (DFT) model was found to be well-matched to the experimental optical data, as evidenced by the UV–vis spectra. Both cyclic voltammetry (CV) and ultraviolet photoelectron spectroscopy (UPS) were used to determine the position of the HOMO with varying results. The values obtained by CV were deeper than those obtained via UPS and correlated well with the theoretical calculations. However, the UPS values were more consistent with the expected outcomes for a system with segregated frontier molecular orbitals (FMOs). The UPS results are also supported by the electrostatic potential maps, which indicate that the electron density within the LUMO and HOMO is nearly completely localized along the 2,6- or 4,8-axis, respectively. The summation of the results indicates that strongly electron-withdrawing groups can be used to selectively tune the LUMO level with minor perturbation of the HOMO, something that is challenging to accomplish in typical donor–acceptor systems.We thank Dr. Norman Lee, Stephon Betts, and Dr. Paul Ralifo from the Chemical Instrumentation Facility at Boston University for compound analysis. We also thank Margaret Chern from the Dennis Lab at Boston University for assistance in obtaining fluorescence lifetimes and quantum yields. Next, we thank Volodimyr Duzhko at the Center for Electronic Materials and Devices at the University of Massachusetts-Amherst. We also thank the National Science Foundation (CHE-141373, CHE-1640298, and CHE-1413207) as well a supercomputer allocation by the Extreme Science and Engineering Discovery Environment (XSEDE) for the Comet supercomputer cluster provided by the San Diego Supercomputing Center (DMR-160146) for supporting this work. (CHE-141373 - National Science Foundation; CHE-1640298 - National Science Foundation; CHE-1413207 - National Science Foundation)Accepted manuscrip