Synthesis and photochromic properties of spiro[naphthopyran-7′H-benzocyclohepta-5′,8′-dienes]

A series of spironaphthopyrans has been synthesised by the acid-catalysed condensation between either a substituted 1-naphthol or 2-naphthol and the propargylic alcohol derived from the addition of lithium trimethylsilylacetylide to a 7H-benzocycloheptan-7-one with subsequent in situ silyl group removal. The photochromism of the novel spironaphthopyrans was characterised by a bathochromically shifted λmax coupled with a relatively quick initial fade of the photogenerated species relative to the comparable diphenyl substituted model compounds. After initial fading a relatively intense residual colour persisted for the spironaphthopyrans.