Tuning of wavelengths: Synthesis and photophysical studies of iridium complexes and their applications in organic light emitting devices

We have prepared and characterized a series of substituted 2-phenylbenzthiazole (4-CF3, 4-Me, 4-OMe, 4-F, 4-CN, and 3-F) ligands. The intermediate di-irrido and the six-coordinated mononuclear iridium(III) dopants of the above ligands have been synthesized and characterized. These complexes are thermally stable between 275 and 300 degreesC depending upon the types and volatility of substituents. They emit bright yellow to orange light. The peak emission wavelengths of the dopants can be finely tuned depending upon the electronic properties of the substituents as well as their positions in the ring. In the absorption spectra, the (MLCT)-M-1 and (MLCT)-M-3 transitions have been resolved in the range of 385-450 nm. The long tail toward lower energies are assigned to (MLCT)-M-3 and (3)pi-pi(*) transitions, which gains intensity by mixing with the higher lying (MLCT)-M-1 state through the spin-orbit coupling of iridium(III). All complexes exhibit one electron oxidation and the oxidation potential values can be correlated with the Hammett substituent constants. The electroluminescent characteristics for the substituted and the unsubstituted complexes have been compared and discussed.