Pursuing the holy grail of thermally activated delayed fluorescence emitters: a molecular strategy for reducing the energy gap and enhancing spin–orbit coupling

state, involving electron density on the halogen, is particularly important for SOC enhancement in the chlorine derivative. These findings highlight that combining a mild heavy-atom effect (HAE) with the control of selective molecular vibrations offers a promising strategy for the design of efficient blue TADF emitters. Our results provide valuable insights for advancing the development of high-performance organic light-emitting materials.