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 has been 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 2f, 2h, and 6e, which are highly emissive with blue emission in their solid states as well as in solution states in most solvents. In addition, the compounds 6e, 6g and 6i were found to be the most cell permeable in HeLa cells for live cell imaging with negligible phototoxicity.