Direct demonstration of triplet excimer in purely organic room temperature phosphorescence through rational molecular design

Organic luminogens with room temperature phosphorescence (RTP) have been paid great attention and developed rapidly for their wide application values. Until now, the internal mechanism and source of phosphorescence are still obscure, especially for the relationship between molecular dimer and RTP emission. Hence, we designed and synthesized eight phenothiazine 5,5-dioxide derivatives to directly reveal how the monomer and dimer in packing affect the RTP behavior. Dimers with strong π–π stacking (β ≤ 20.66°; d ≤ 3.86 Å) lead to pure triplet excimer emission, while those with weak π–π stacking (27.02° ≤ β ≤ 40.64°; 3.84 Å ≤ d ≤ 4.41 Å) contribute to dual RTP emissions of both monomer and triplet excimer. The valuable information of this work would promote the further development of this research field, as well as others in aggregate.