Raw data for manuscript titled 'Vibrationally-assisted intersystem crossing in benchmark thermally activated delayed fluorescence molecules.' Data includes absorption and photoluminescence spectra for 2CzPN and 4CzIPN (Fig1b_Abs_2CzPN, Fig1b_Abs_4CzIPN, Fig1b_PL_2CzPN, Fig1b_PL_4CzIPN); transient electron spin resonance spectra for 2CzPN and 4CzIPN (Fig2c_2CzPN_0p4us, Fig2d_4CzIPN_0p4us); probability distributions for zero-field splitting in 2CzPN and 4CzIPN (Fig3a_2CzPN_ZFS_probability_distribution, Fig3b_4CzIPN_ZFS_probability_distribution); plots of zero-field splitting as a function of overlap index in 2CzPN and 4CzIPN (Fig3c_2CzPN_ZFS_overlap_idx, Fig3d_4CzIPN_ZFS_overlap_idx); and density plots (field versus time) of transient electron spin resonance spectra of 2CzPN and 4CzIPN (FigS1_TrESR_2CzPN_420nm_exc, FigS1_TrESR_4CzIPN_460nm_exc).