Photocyclization of a 1,1′-bisnaphthalene: planarization of a highly twisted biaryl system after excited state ArOH dissociation

Photolysis of the highly twisted 1,1′-bisnaphthalene 6 gives the much more planar dinaphthopyran 10 with high quantum yield (Φ = 0.17) in aqueous MeCN, demonstrating that the expected enhanced electronic communication between the connected aromatic rings of biaryls in S 1 is sufficient to drive thermally unfavourable reactions requiring initial planarization of these biaryl systems.