Ultrafast Spectroscopic\nInvestigation of the Aggregation\nInduced TADF from High-Level Reversed Intersystem Crossing

The thermally activated delayed fluorescence (TADF) originating\nfrom high-level intersystem crossing (hRISC) presents great potential\nin realizing a more full utilization of triplet excitons. In this\nstudy, DPA-FBP and TPA-FBP were doped in a PMMA film with different\nweight fractions to study the effect of aggregation on the luminescence\nproperties. As a result, the TADF feature from hRISC was only found\nin the 50 wt % doped film, whereas the 1 wt % doped film only shows\nprompt fluorescence. The fs-TA spectroscopy results reveal that the\n50 wt % film will generate charge transfer species to lower the energy\ngap, so that the high-lying triplet exciton can transition back to\nthe singlet state, whereas that of the 1 wt % film will quickly transition\nto the lowest triplet state due to the unfavorable energy splitting.\nThis study provides a new insight into aggregation effects on the\nexcited-state properties of hot exciton materials and the solid-state\nphotodynamic.