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 pi-conjugation length (6 and 7). The results indicate that singlet-triplet energy splitting (Delta E-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 Delta E-ST but also enhances k(r). For compound 7, the k(r) value is comparable with compound 6, but Delta E-ST value is quite large. Therefore, possessing an appropriate pi-conjugation length might be helpful to improve TADF performances for the materials investigated here. (C) 2016 Elsevier B. V. All rights reserved.