Effect of substituents on the photoluminescence performance of Ir(III) complexes: Synthesis, electrochemistry and photophysical properties

We have prepared and characterized a series of substituted imidazole ligands namely dmmppi, dmmpfpi, dmdmppi and dmdmpfpi. These compounds will readily undergo cyclometalation with iridium trichloride and form di-irrido and the six coordinated iridium(III) dopants of the substituted imidazole ligands. They emit green colour both in solid and in solution phase. The peak emission wavelength of the dopants (λmax = 428–497 nm) can be finely tuned depending upon the electronic properties of the phenyl, fluorophyenyl, methoxy phenyl and dimethoxyphenyl substituents as well as their positions in the imidazole ring. These iridium complexes namely Ir(dmmppi)2(pic) 1a, Ir(dmmpfpi)2(pic) 1b, Ir(dmdmppi)2(pic) 1c and Ir(dmdmpfpi)2(pic) 1d were characterized by 1H NMR, MS and elemental analysis. All these iridium complexes 1a–1d show unusual high HOMO levels (EHOMO = 5.21–5.41 eV) and high phosphorescence. These complexes emit green light with exceedingly high efficiency.