Synthesis and Characterization of Perfluoroaryl-Substituted Siloles and Thiophenes:  A Series of Electron-Deficient Blue Light Emitting Materials

Perfluoroaryl (Arf)-derivatized siloles and thiophenes have been synthesized via nucleophilic aromatic substitutions (SNAr) involving reactions of hexafluorobenzene, octafluoronaphthalene, and decafluorobiphenyl with the appropriate dilithiosilole or dilithiothiophene intermediate. These compounds are of interest as electron-transport layers and/or blue light emitters, as they possess relatively low LUMO energy levels while maintaining high HOMO−LUMO gaps. Siloles and thiophene 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 and 3.56 eV, while photoluminescence emission spectra reveal λmax,ems values from 396 to 506 nm (corresponding to violet to blue/green emission). Dilute solution-state quantum yields varied from 0.01 to 0.10 for the silole compounds and from 0.25 to 0.71 for the thiophene-based compounds. The experimentally determined LUMO levels (ca. −2.6 to −2.9 eV, as determined by cyclic voltammetry) suggest that these compounds are good candidates for electron-transport layers. DFT calculations were used to investigate the electronic properties of the compounds, and a preliminary assessment of charge transport and electroluminescent behavior was made.