Synthesis and photophysical activity of 6-substituted isocoumarins

6-Substituted isocoumarins with aryl, alkynyl, and diphenyl-amino substituents were synthesized from 4-bromobenzoic acid by annulation with tolane via rhodium-catalyzed C–H activation followed by palladium-catalyzed cross-coupling reactions. The compounds obtained exhibit luminescence emission in the violet–blue region (370–480 nm) with quantum yields up to 95% (for the diphenylamino derivative). Aggregation of biphenyl-substituted isocoumarin leads to a strong bathochromic shift (by 80 nm) of emission as a result of intermolecular π–π stacking interactions.