Highly efficient ultralong organic phosphorescence induced by lone pair repulsions and noncovalent interactions

Persistent room temperature phosphorescence (pRTP) has aroused increasing interest. Here we report an ortho-substituted compound in which two o-bromophenylsulfides and a carbazolyl were joined by a phenyl ring. The abundant intra- and inter-molecular noncovalent interactions inhibit the non-radiative transition and make this compound prone to forming a physical dimer which has a stabilized emissive triplet state. The confined space and the repulsion from lone pairs of sulphur atoms rigidize the molecular structure. The compound exhibits a long afterglow of over 2 s with a phosphorescence quantum efficiency (phi(p)) of 19.0% and a lifetime of over 250 ms. The photoluminescence properties under the aggregational state are also rationalized by computational calculations based on the intermolecular interactions and spin-orbit coupling (SOC) constant.