Ambient Phosphor with High Efficiency and Long Lifetime in Poly(Methyl Methacrylate) Through Charge-Transfer-Mediated Triplet Exciton Formation for Photolithography Applications

Currently, purely organic compounds showing ambient phosphorescence with high efficiency (ΦP ) and ultra-long lifetime (τP ) are quite rare and often need to be achieved in hydrophilic poly(vinyl alcohol)-based hosts. This severely limits their applications. Here, we provide a solution to this issue by constructing an ortho-linked donor-acceptor (D-A) dyad whose D moiety has not only a long-lived T1 state to achieve a long τP , but also a Tn state that is close to the S1 state of the dyad to trigger effective spin-orbit charge transfer intersystem crossing (SOCT-ISC). The rationality of this strategy was validated by a new phosphor OF-BCz that is able to show a τP of 1.92 s and a ΦP of 30 % even in a less rigid matrix of poly(methyl methacrylate) (PMMA). Excitingly, OF-BCz exhibited its potential as both a photocuring initiator and an in situ quality indicator, allowing for the visual detection of defects in photolithographic patterning.

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

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.