This emission is red-shifted compared to those of DDiKTa (lPL = 470 nm) and DiKTa (lPL = 453 nm). The emission of DDiKTa-F shows a modest positive Wavelength / nm solvatochromism (Figure ), which is consistent with an emissive excited state of SRCT character. The energies of the S1 and T1 states, determined from the onsets of the steady-state PL and phosphorescence spectra at 77 K in 2-MeTHF glass, respectively, are 2.64 and 2.44 eV (Figure ), thus the DEST is 0.20 eV. This value is similar in magnitude to those of DiKTa (0.22 eV in frozen toluene) and DDiKTa (0.21 eV in frozen toluene). The photoluminescence quantum yield, FPL, in toluene is 34%, this decreases to 31% upon exposure to air (Figure ). No delayed emission was observed in toluene and the lifetime of the emission decay, τPL, is 4.5 ns (Figure ), which is similar to that of DiKTa (τPL= 5.1 ns). With a view to employing DDiKTa-F as an emitter in an OLED and to cross-compare its device performance to those with DDiKTa and DiKTa we next investigated the photophysical properties of this emitter as doped films in 1,3-bis(N-carbazolyl)benzene (mCP). The 2 wt% doped film of DDiKTa-F in mCP emits at lPL of 494 nm, with a FWHM of 49 nm (Figure ), an emission that is red-shifted compared to that of DDiKTa (lPL = 491 nm) and DiKTa (lPL = 467 nm) in 2 wt% doped films in mCP. We identified that 2 wt% doping provided the highest FPL of 78%, while the FPL decreased to 43% and the PL spectrum showed a pronounced red-shift from 491 to 507 nm when the doping concentration increased to 10 wt% from 1 wt% (Figure ), which implies that aggregation becomes an issue at this higher doping concentration.