where 〈𝑆𝑂𝐶(𝑇 1 , 𝑆 0 )〉 is the SOC matrix between T1 and S0, γ is the broadening of the line-shape function for ISC (Fig. ). The SOC (T1, S0) of 0.71 cm -1 in BTD-FL increases significantly to 1.84 cm -1 in BTD-FLBr due to the partial hole distribution from direct-linked bromine to T1, which triggers a much stronger nonradiative decay (Fig. and Supplementary Fig. ). However, the SOC (T1, S0) of BTD-HeBr not increases but decreases slightly to 0.69 cm -1 , displaying such through-space heavy atom strategy can effectively suppress triplet nonradiative decay to achieve efficient X-ray detection and imaging.