Thiophene-fused phospholo[3,2-b]phospholes and their dichalcogenides: Synthesis and structure–photophysical properties relationships

The PCl₃-promoted intramolecular cascade cyclization produced a series of thiophene-fused phospholo3,2-b]phosphole derivatives, including non-oxidized 2, dioxides 3, and disulfides 4. These derivatives exhibit significantly red-shifted absorptions and fluorescences compared with their benzene-fused analogues. Among the thiophene-fused series, the non-oxidized 2 has the highest fluorescence quantum yield of 0.95. This trend is in contrast to that observed for the benzene analogues, in which a dioxide derivative shows the most intense fluorescence.