Photo- and Oxygen- Synergistically Controlled Selective Expression of Organic Phosphorescence Units

Abstract

Dynamic control of ultralong organic room-temperature phosphorescence (UORTP) is a charming target. Herein, we report a stimuli-responsive phosphorescence unit 7H-indolo[2,3-c]quinoline (NBCz) and its derivatives (PCBNBCz, FSO 2 NBCz, and N 2 BCzSO 2 NBCz) that show photo-and oxygen-synergistically induced afterglow activation and afterglow color change in the PMMA film. PCBNBCz and FSO 2 NBCz feature a donor− acceptor (D−A) structure, and N 2 BCzSO 2 NBCz features acceptor-bridged two different phosphorescence units (NBCz and N 2 BCz). The photoactivated UORTP of PCBNBCz and FSO 2 NBCz arises from the photoinduced consumption of oxygen in the PMMA film. It is clear that the phosphorescence unit NBCz contributes to subsequent photoinduced UORTP color change because the NBCz-doped PMMA film shows the same UORTP color change process. ESR and HRMS measurements confirmed that oxidation of NBCz occurs at the nitrogen atom of the quinoline ring via photogenerated superoxide radicals, which results in the UORTP color change. TDDFT calculations proved that after oxidation of NBCz, the T 1 energy level declines significantly. Furthermore, photocontrolled selective expression of phosphorescence units is achieved in the case of N 2 BCzSO 2 NBCz. After further UV irradiation, oxidation of NBCz happened, and the oxidized form N 2 BCzSO 2 NBCz-O emitted the intrinsic orange UORTP of NBCz-O selectively and screened the intrinsic yellowish-green UORTP of N 2 BCz. Finally, multilevel photolithography can be demonstrated based on the photoactivated UORTP and the photoinduced UORTP color change. This work may give a deep insight into organic phosphorescence and pave a simple way for the development of stimulus-responsive smart UORTP materials.