Isomeric Engineering of Organic Luminophores for Multicolor Room Temperature Phosphorescence Including Red Afterglow

Abstract Manipulating and optimizing the room temperature phosphorescence (RTP) behavior of organic luminophores is highly desirable for exploring their extensive potential applications. However, achieving tailored and precise control over RTP emission colors remains a challenging task. Herein, three regioisomers, namely o‐Br, m‐Br, and p‐Br, are developed by directly bonding the nitrogen atom of commercial carbazole and the sulfur atom of the sulfonylbenzene group. This design not only features the bromine substitution at different positions but also leads to the formation of N─S═O resonance linkages. With the variation in position of bromine from ortho to para, the RTP color changes from yellow to red. Experimental investigations and theoretical calculations demonstrate that this color variation arises from the modulation of contributions from different canonical forms of N─S═O, which can be attributed to the regioisomerization of bromine atoms for fine‐tuning intra‐ and intermolecular interactions. Additionally, the in vitro cell imaging is successfully realized by employing red RTP nanoparticles prepared from the p‐Br luminophore. This study reveals a simple and effective approach for customizing RTP emission colors through the integration of isomerization and resonance variation control.