Intramolecular Electrophilic Cyclization Approach to 6-Substituted Naphtho[2,1-b]benzofurans: Novel Dual-State Emissive Fluorophores with Blue Emission

A regiospecific synthesis of naphtho[2,1-b]benzofurans with a substituent at the C6 position was achieved via intramolecular 6-endo-dig electrophilic cyclization under acidic conditions to construct the central aromatic C ring. Screening of the synthesized compounds using a high-content imaging system enabled us to discover novel dual state emissive compounds 2{1,6}, 2{1,8}, and 2{4,3}, which are highly emissive with blue emission in their solid states as well as in solution states in most solvents. In addition, the compounds 2{4,3}, 2{4,12}, and 2{5,13} were found to be the most cell permeable in HeLa cells for live cell imaging with negligible phototoxicity.