Room Temperature Phosphorescence in Solution from Thiophene‐Bridged Triply Donor‐Substituted Tristriazolotriazines

Most organic room‐temperature phosphorescence (RTP) emitters do not show their RTP in solution. Here, we incorporated sulfur‐containing thiophene bridges between the donor and acceptor moieties in D3A‐type tristriazolotriazines (TTTs). The thiophene inclusion increased the spin‐orbit coupling associated with the radiative T1→S0 pathway, allowing RTP to be observed in solution for all compounds, likely assisted by protection of the emissive TTT‐thiophene core from the environment by the bulky peripheral donors. The accelerating effect of heavy sulfur atoms on intersystem crossing leads to phosphorescence at room temperature even in solution from tristriazolotriazines decorated via thiophene bridges with three bulky peripheral donor units.