Synthesis and photochromic properties of symmetrical aryl ether linked bi- and tri-naphthopyrans

A range of aryl ether linked benzophenones (8) has been conveniently obtained by nucleophilic displacement of fluoride from 4-fluorobenzophenone with a dihydroxy-benzene or -naphthalene. The linked benzophenones were efficiently transformed in two steps to symmetrically linked naphthopyrans (10d–k). The photochromic response of these novel systems under steady state irradiation is characterised by a two stage fading process and their colourability is only marginally improved over the related monomeric analogues (10a–c).