Acquiring Charge‐Transfer‐Featured Single‐Molecule Ultralong Organic Room Temperature Phosphorescence via Through‐Space Electronic Coupling

Abstract 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 (S 1 ) that shows a 1 CT character to the first triplet excited state (T 1 ) that exhibits a local excited state feature ( 3 LE), and then to the second triplet excited state (T 2 ) that shows a 3 CT character (i.e., S 1 ( 1 CT)→T 1 ( 3 LE)→T 2 ( 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.