Orientation of nitration in bay-region of benzothioxanthene imide: A streamlined pathway to N- and S-annulated derivatives

N-annulation has recently emerged as a powerful approach for modulating the optoelectronic properties of benzothioxanthene imide (BTI) derivatives, enabling their application in areas ranging from light-emitting devices to photodynamic therapy. In this study, we report an optimized synthetic strategy that reduces the original seven-step process for N-annulated BTIs to just four steps, achieving a ∼40 % improvement in efficiency. Additionally, we introduce a novel S-annulated BTI derivative, extending the scope of heteroatom-involving ring fusion. Comparative analysis between N- and S-annulated compounds reveals the pronounced influence of a single-atom modification on the π-conjugated system. These findings demonstrate the utility of annulation as a chemically accessible and versatile tool for fine-tuning molecular architectures with tailored photophysical properties.