Another aspect that is especially relevant for vis-to-UV TTA-UC is the exaggerated thermodynamic driving force for TTA typically found in UV emitting species. This is the case for the compounds investigated herein: [2 ´ E(T1) -E(S1)] ≥ 0.7 eV for all species, with PPD in particular having a driving force of almost 1.6 eV. If this substantial energy loss could be mitigated substantially larger apparent anti-Stokes shifts could be realized. The relative lowering of the triplet energies should perhaps be the primary focus as this would enable excitation at longer wavelengths than currently possible. A few studies have investigated substituent effects on the energetic landscape of polyacene emitters, Controlling not only the energy of T1 but also of T2 is of significance. In molecules, such as perylene and rubrene, in which the spin-statistical factor f has been determined to lie above the commonly encountered value of 2/5, the energy difference [2 ´ E(T1) -E(T2)] < 0. In perylene this difference is strongly negative, efficiently shutting down the creation of the T2 state upon TTA, causing f to approach unity. In rubrene, however, f is reported to lie around 0.6 in solution, and the creation of T2 during TTA is only slightly endothermic. A recent study by Bossanyi et al. verify that T2 is formed during TTA in rubrene, but that the energy alignment between T2 and S1 allows fast high-level rISC (HL-rISC) from T2 to S1 to occur, outcompeting non-radiative decay from T2 to T1. HL-rISC has been found also in anthracene derivatives (not DPA however) and should be considered as a potential avenue to increase f beyond 2/5. This pathway is very sensitive to the precise alignment of S1, T1, and T2 energies, and the study by Bossanyi et al. suggest that in cases where [2 ´ E(T1) -E(T2)] approaches zero f may in fact approach unity in molecules where HL-rISC occurs. Finally, from simulations the same study states that intermolecular geometry can affect f, with parallel geometries giving rise to higher values. For the annihilators used herein [2 ´ E(T1) -E(T2)] is expected to be much greater than zero. Additionally, S1 is expected to lie several hundreds of meV above T2 for most annihilators (Table ), suggesting that HL-rISC is inefficient in these molecules. Most of the investigated annihilators show an expected value of approximately 0.4, but our results also indicate that f takes a larger value than 2/5 in TIPS-Naph (0.54) but a lower value for PPD (0.22, Table ).