The absorption spectra of the complexes were measured in toluene solution (Figure ). All possess two low-energy, low intensity absorption bands at ca. 400 and 450 nm, with molar extinction coefficients, e, between ca. 2000 and 6000 M -1 cm -1 (Error! Reference source not found.). The two low energy bands in most of the complexes are assigned to S0→S2 and S0→S4 transitions that have larger oscillator strengths (f > 0.02) than the S0→S1 and S0→S3 transitions (f < 0.01). The S2 excited state comes from a HOMO→LUMO+1 transition, while the S4 excited state comes from a HOMO→LUMO+3 transition, both excited states possess mixed 1 MLCT/LLCT character. However, the three complexes with a trimethylsilyl group at the C4 position (C4, C4N4 and C4N5) show distinct absorption profiles as the lowest energy absorption bands for these complexes are assigned to the S0→S1 transition. High energy transitions below 300 nm result from local π-π* excitation of the ppy ligands, as previously reported for ppy-containing iridium complexes. The emission properties of the nine complexes in degassed dilute toluene are shown in Figure . Each of the complexes showed bright green emission with λPL between 506 and 533 nm (). There is a modest reduction in the FWHM of the emission spectra of the trimethylsilyl-substituted complexes, with FWHM ranging between 72 and 77 nm (2510-2680 cm -1 ), compared with the FWHM of 81 nm (2940 cm -1 ) for IrPic. CIE 1931 colour coordinates are reported in Table and the coordinates plotted in Figure . Complexes with substitution at the 4-position of the phenyl ring (C4, C4N4 and C4N5) possess a red-shifted emission (λPL = 524 to 533 nm) that is consistent with the destabilized HOMO observed in the electrochemistry.