Triptycences as thermally activated delayed fluorescence materials: Effect of π-conjugation length and donors

Highlights: • The ΔE_ST of compounds 2–5 is reduced largely, but the increase of k_r is small. • The compound 6 not only reduces the ΔE_ST but also enhances k_r. • The k_r of compound 7 is comparable with that of compound 6, but the ΔE_ST is large. Based on a thermally activated delayed fluorescence (TADF) triptycene compound 1, compounds 2–7 were designed by varying electron-donating units (2–5) and increasing π-conjugation length (6 and 7). The results indicate that singlet-triplet energy splitting (ΔE_ST) of compounds 2–5 is reduced largely, but their improvement of radiative decay rate (k_r) is slightly small. However, the compound 6 not only reduces the ΔE_ST but also enhances k_r. For compound 7, the k_r value is comparable with compound 6, but ΔE_ST value is quite large. Therefore, possessing an appropriate π-conjugation length might be helpful to improve TADF performances for the materials investigated here.