To explore the nature of excited states of the two emitters, we performed a solvatochromism study by measuring the absorption and emission spectra in different solvents (Figure , 2c, Figure and Tables and). There is only a very small degree of positive solvatochromism observed for TPPO-tBu-DiKTa, which confirms that the emissive S1 state has SRCT character. In contrast, TPA-tBu-DiKTa shows a SRCT-dominated emission in low polarity solvents; while, in higher polarity solvents, dual emission is observed as the LRCT state between the TPA donor and the tBu-DiKTa core becomes accessible and even lower in energy than the tBu-DiKTa-based SRCT state. We have documented such behavior previously in donor-substituted DiKTa derivatives. The relationship between the Stokes shift and solvent polarity was explored (Equation S1-S3). As shown in Figure DiKTa (0.20 eV) and close to the calculated ones (0. DEST and the competing non-radiative decay processes with ISC/RISC. By contrast, the emission of TPA-tBu-DiKTa decays with multiexponential kinetics, with prompt lifetimes, τp, of 3.2 and 14 ns and a delayed lifetime, τd, of 18 µs (Figure ). The additional longer prompt and delayed lifetime components of TPA-tBu-DiKTa compared to TPPO-tBu-DiKTa may originate from the radiative decay from the LRCT state, which would have a lower oscillator strength and thus a slower radiative decay rate, kr, than that from the SRCT state. The presence of a low-lying LRCT state may result in smaller DEST, which facilitates the RISC process. To verify this hypothesis, steady-state PL spectra and time-resolved PL decays of TPA-tBu-DiKTa in degassed methylcyclohexane (Me-CyHex) and chloroform were also measured (Figure ).