Efficient and tunable purely organic room temperature phosphorescence films from selenium-containing emitters achieved by structural isomerism

Abstract

Metal-free purely organic room temperature phosphorescent (RTP) materials that can exhibit high RTP efficiencies in film states are highly desired. Herein, we report three donor–acceptor isomers (1, 2, and 3) based on a 9-phenyl-9H-carbazole donor and a 9H-selenoxanthen-9-one acceptor unit, which show phosphorescent emission in doped films. The substitution position of the donor unit on the 9H-selenoxanthen-9-one acceptor unit can significantly impact their photophysical properties. In the doped film state, 1 and 2 show bright blue and green RTP with high phosphorescent quantum yields of up to 66.7%, while 3 only exhibits weak fluorescence emission at room temperature and yellow phosphorescence at cryogenic temperature. Through both photophysical and theoretical investigations, effective regulation of the non-radiative transition process of their lowest-lying triplet excited states by isomerization engineering was identified as the origin of their different light-emitting behaviors. Moreover, a 2-based phosphorescent film sensor for trace oxygen detection is fabricated, which exhibits a wide detection range (0–2.1 × 10⁵ ppm), high quenching constant (2.22 × 10⁻⁴ ppm⁻¹), and low detection limit (2.8 ppm), demonstrating their application potential as visual sensory materials.