In the non-polar Me-CyHex, the emission is both bluer and narrower (lPL = 467 nm; FWHM of 30 nm), with a fast τp of 6.2 ns and no observed delayed emission, which is similar to the photophysical behavior of TPPO-tBu-DiKTa, implying emission from a SRCT state. In higher polarity chloroform, the emission is much redder and broader The propensity for these two compounds to aggregate and show aggregation induced emission (AIE) was investigated across a series of THF/water solutions with increasing water content. As shown in Figure , with the increase of water fraction (fw) from 0 to 90%, the emission intensity of TPPO-tBu-DiKTa progressively drops as the emission red-shifts, which is linked to a progressively stabilized emissive CT state with increasing polarity; thus, this compound does not show AIE. By contrast, the emission intensity of TPA-tBu-DiKTa decreases first when the fw increases from 0 to 60% but then increases significantly and the spectra blue-shift from 588 to 564 nm when the fw is higher than 60%, which indicates that TPA-tBu-DiKTa shows AIE behavior, meaning that there is a strong suppression of nonradiative decay in the aggregated state. With a view to exploiting these materials as emitters for OLEDs, the photophysical properties of films were then investigated. 1,3-bis(N-carbazolyl) benzene (mCP) was used as the host material because of its suitably high triplet energy (2.9 eV). The absolute FPL values of TPPO-tBu-DiKTa and TPA-tBu-DiKTa at different doping concentrations in mCP were measured under a nitrogen atmosphere (Table ). Due to the suppressed non-radiative decay in the rigid matrix and the interaction between host and guest materials, the FPL values in mCP films are higher than those in dilute toluene. TPPO-tBu-DiKTa and TPA-tBu-DiKTa have the highest FPL value of 85 and 96% in 2 wt% doped films in mCP; indeed, the FPL of the 1, 5, 10 and 15 wt% doped films of TPPO-tBu-DiKTa in mCP progressively decrease from 84% to 73, 67 and 63% without any major changes to the PL spectra (Figure ). For TPA-tBu-DiKTa, the FPL is 93 and 96% for the 1 and 5 wt% doped films in mCP, while the value decreases to 83% for the 10 wt% doped films. When increasing the doping concentrations to 15 and 25 wt%, the emission broadens and red-shifts while the FPL decreases to 76 and 73%, respectively (Figure ). Contributions from intermolecular CT states cannot be ruled out. Compared to the larger decreases of the reported FPL for DiKTa (51, 37 and 16% in 1, 5 and 10 wt% doped films in mCP) and Mes3DiKTa (52, 38, 42 and 26% in 3.5, 5, 10 and 20 wt% doped films in mCP), the generally higher absolute values and smaller decreases in FPL for TPPO-tBu-DiKTa and TPA-tBu-DiKTa illustrate clearly that the ortho-substituted groups help to suppress ACQ.