Synthesis and characterization of perfluoroaryl derivatized compounds for use as n-type materials in organic electronic applications

This dissertation describes the synthesis, characterization, and preliminary device performance of a number of high electron affinity organic compounds. These systems, which combine the stabilized LUMO energy level of a heterole fragment with the electron-deficient pi-system of a perfluoroaromatic framework, are of interest as electron transport layers and/or high energy emitters for a variety of electronic applications.;Perfluoroaryl-derivatized siloles and thiophenes have been synthesized via nucleophilic aromatic substitution (SNArF) reactions. Siloles and thiophenes were modified in the 2 and 5 positions, while bithiophene substitution occurred in the 5 and 5' positions. The HOMO-LUMO gaps, as determined by UV-vis spectroscopy, range between 2.79 to 3.56 eV, while photoluminescence emission spectra reveal violet to blue/green emission. Dilute (optical density 0.1) solution state quantum yields varied from 0.01 to 0.10 for the silole compounds, and 0.25 to 0.71 for the thiophene-based compounds. The experimentally determined LUMO levels of -2.6 to -2.9 eV are within the range established for electron-conducting materials. Preliminary assessments of electron transport (field effect transistor and organic light emitting diode (OLED) configurations) and electroluminescent behavior (OLED configuration) demonstrate that these systems function well as both electron transport materials and high energy emitters.;A series of 2,7-substituted hexafluoro-9-heterofluorenes and a series oligothiophene/fluorinated-heterofluorene-containing donor-acceptor compounds (DA) were synthesized via a combination of nucleophilic aromatic substitution (SNArF) and palladium coupling reactions. Single crystal X-ray analyses of a number of compounds revealed cofacial packing in all cases, with intermolecular distances as short as 3.2 A. Long range order in the solid state is highly dependent on the heteroatom substituent and the 2,7-substituents. The HOMO-LUMO energy gaps, as determined by UV-vis spectroscopy, range from 3.0 to 3.9 eV, for the hexafluoro-9-heterofluorenes and from 2.4 to 2.7 eV for the DA compounds. The LUMO energy levels, -2.7 to -3.5 eV, are relatively independent of changes in heteroatom or heteroatom substitutent, which suggests that these components can be modified to optimize solid state and film forming properties. Dilute solution-state quantum yields vary significantly with the identity of the heteroatom and the 2,7-substituents, and approach a value of 1 for a number of the 2,7-substituted hexafluoro-9-heterofluorenes. Donor-acceptor compounds exhibit dilute solution state quantum yields that are significantly lower than those of the pure acceptor heterofluorenes (0.02--0.38 for the DA compounds vs. ∼ 1 for the pure acceptors). Additionally, significant solvatochromism in both emission energy and emission intensity was observed for all the DA systems, which suggests the existence of a charge-separated excited state. Unoptimized photovoltaic devices made with blends of fluorinated heterofluorene and poly-3-hexylthiophene (P3HT) exhibit open circuit voltage values as high as 0.905 V, and improved overall device efficiencies with respect to P3HT-only devices.