Selective Expression of Organic P hosphorescence Units: When H-Benzo[f]indole Meets 7H-Benzo[c]carbazole

Phosphorescence selective expression in the development of ultralong organic room-temperature phosphorescence (UORTP) materials to enrich the properties and functions of smart materials is a very interesting topic but has not been realized yet due to the lack of organic phosphorescence units. In this work, we, for the first time, investigate the selective expression phenomenon of two organic phosphorescence units in a single molecule. First, we report a new phosphorescence unit 7H-benzo[c]carbazole (BCz) with the advantage of simple synthesis. BCz derivatives (PNBCz-1 and PNBCz-2) feature photoactivated green ultralong phosphorescence in the PMMA film at room temperature, and cation radicals are involved in the unique ultralong phosphorescence behavior, which is similar to H-benzo[f]indole (Bd) derivatives. Different from Bd, pure powders of BCz derivatives show intense red-shifted ultralong phosphorescence at 77 K, probably due to the extended π conjugated structure of BCz. Then, BCz and Bd were incorporated into a single skeleton and two asymmetric molecules (PNBCzBd-1 and PNBCzBd-2) were obtained. Surprisingly, in the PMMA film, PNBCzBd-1 and PNBCzBd-2 both show photoactivated yellow ultralong phosphorescence at room temperature assigned to the intrinsic phosphorescence emission of Bd, and intrinsic green phosphorescence of BCz is almost screened by Bd. Density functional theory (DFT) calculations reveal that the incorporation of Bd leads to the shifting of the phosphorescence emission centers from BCz units to Bd units. Therefore, the intrinsic phosphorescence emission of Bd is selectively expressed in the case of PNBCzBd-1 and PNBCzBd-2. To our best knowledge, this is the first example that reports the selective expression behavior of organic phosphorescence units. We believe that this study may impact the future research of UORTP materials and lay the foundation for their future applications.