Synthesis and characterization of fluorene and carbazole dithienosilole derivatives for potential applications in organic light-emitting diodes

Several fluorene or carbazole-based dithienosiloles (DTSs) have been synthesized and their thermal, photophysical, and electrochemical properties have been systematically investigated. These compounds show high thermal stability with glass transition temperature above 110 °C as well as decomposition temperatures at ∼400 °C. Intense green emission is observed in the spectral region of 500-510 nm for all compounds (ΦPL=0.31-0.80), that is, attributed to both the 5,5′-substituents of the DTS ring and DTS-based π-π∗ transition. Based on the emission spectra at 77 K, the triplet energy for these compounds was calculated to be within 2.1-2.2 eV, indicating that they may be used as host materials for red emitters in organic light-emitting diodes (OLEDs). All compounds exhibit reversible oxidation and possess low-lying LUMO energies, owing to the conjugated fluorene/carbazole substituents on the DTS. This along with the high thermal/electrochemical stabilities and high fluorescent quantum efficiencies makes the new DTSs compounds promising candidates for use in OLEDs as emitters, host and electron-transporting materials.