More Than Carbazole Derivative Activates Room Temperature Ultralong Organic Phosphorescence of Benzoindole Derivative

Herein, we report four carbazole/1H-benzo[f]indole (Cz/Bd) derivatives with increasing Bd substitution (Bd number=0~3), which give a general mechanism for Bd-based ultralong organic phosphorescence. To physically isolate Cz and Bd, we synthesized Cz and Bd in the lab, separately. According to experimental results, we draw several important points. The first important point is that Bd and its derivatives commonly possess two groups of intrinsic phosphorescence bands, of which short-lifetime band at ~450 nm is assigned to the molecular phosphorescence of their neutral molecules and of which typical ultralong phosphorescence bands at 560 nm, 610 nm and 660 nm are assigned to their radical cations. Amazingly, PMMA films (1wt.%) of CNCzBdBr and CN2BdBr both demonstrate photo-activated room-temperature ultralong organic phosphorescence while this doesn’t happen to Bd and CN3Bd. The second important point is that activation of ultralong phosphorescence from Bd derivatives involves three factors: well dispersion with limited amount in matrix, generation of Bd derivatives’ radical cations and stabilizing radical cations mediated by matrix. Cz derivative can function as a matrix to activate (room temperature) ultralong organic phosphorescence of Bd derivative but its activation function can be replaced by other methods such as photo-activation. The third important point is that the photo-activated ultralong organic phosphorescence is closely related to molecular structure of Bd derivative and stability of its radical cation. The fourth important point is that for double-carbazole system with trace isomer its room temperature ultralong organic phosphorescence originates at least from synergistic effect of monosubstituted product and disubstituted product of Bd. Furthermore, it is discovered that several other matrixes can also activate room-temperature ultralong organic phosphorescence of Bd derivatives, further verifying the second important point. To our best knowledge, this study is a big breakthrough in ultralong organic phosphorescence and will probably open a new era for its development.