Acquiring Charge-Transfer-Featured Single-Molecule Ultralong Organic Room Temperature Phosphorescence via...

Although long-lived triplet charge-transfer (³ CT) state with high energy level has gained significant attention, the development of organic small molecules capable of achieving such states remains a major challenge. Herein, by using the through-space electronic coupling effect, we have developed a compound, namely NIC-DMAC, which has a long-lived ³ CT state at the single-molecule level with a lifetime of 210 ms and a high energy level of up to 2.50 eV. Through a combination of experimental and computational approaches, we have elucidated the photophysical processes of NIC-DMAC, which involve sequential transitions from the first singlet excited state (S₁ ) that shows a ¹ CT character to the first triplet excited state (T₁ ) that exhibits a local excited state feature (³ LE), and then to the second triplet excited state (T₂ ) that shows a ³ CT character (i.e., S₁ (¹ CT)→T₁ (³ LE)→T₂ (³ CT)). The long lifetime and high energy level of its ³ CT state have enabled NIC-DMAC as an initiator for photocuring in double patterning applications.