Tuning the luminescent properties of benzophenanthridine alkaloids based natural products to guide the rational design of NIR BioAIEgens

In this study, the relationship between molecular structure and photophysical properties of representative alkaloids (DHSAN, DHCHE, SAN, CHE) was systematically investigated by combining PCM and QM/MM models. The effects of the open-ring and closed-ring, ionic and non-ionic properties, as well as different environments on photophysical properties of these dyes were examined. We found that the AIE characteristics of open-ring dyes are mainly attributed by suppression of rotation and oscillation motions of O-methyl and N-methyl groups in crystalline states. The closed-ring dyes are insensitive to environments and demonstrate dual emissions due to structural rigidity. The emission of ionic dyes redshifted than those of non-ionic dyes. Especially, the open-ring and ionic dye CHE naturally combining AIE activity and red emission bears the best performance. Further molecular design proposed that the emission of 7-CHE and 8-CHE reach NIR region. This study provides theoretical guidance for rational design of BioAIEgens with pharmacological potential.