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 lambda(max,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.