Neutral Colouring Photochromic 2H-Naphtho[1,2-b]pyrans and Heterocyclic Pyrans and Their Use

A naphtho[1,2-$i(b)]pyran of general formula (I) wherein R?1¿ and R?2¿ are each selected from unsubstituted, mono-, di- or polysubstituted aryl groups, phenyl and naphthyl and heteroaryl groups. R?5¿ is selected from linear or branched C¿1?-C¿10? alkyl, C¿1?-C¿20? cycloalkyl, C¿1?-C¿20? bicycloalkyl, C¿1?-C¿20? polycycloalkyl, linear or branched C¿1?-C¿10? haloalkyl, linear or branched C¿1?-C¿10? perhaloalkyl, linear or branched C¿1?-C¿10? perhaloalkenyl, linear or branched C¿1?-C¿10? alkenyl, C¿1?-C¿10? alkynyl, linear or branched C¿1?-C¿10? alkoxy, linear or branched C¿1?-C¿10? alkylthio, linear or branched C¿1?-C¿10? alkoxy (linear or branched C¿1?-C¿10? alkyl), linear or branched C¿1?-C¿10? hydroxyalkyl, linear or branched C¿1?-C¿10? aminoalkyl, aryl, phenyl, heteroaryl, halogen, nitrile, nitro, amino, linear or branched C¿1?-C¿20? alkoxycarbonyl, hydroxyl, formyl, acetyl, amido, C¿1?-C¿5? alkyl amido, C¿1?-C¿5? dialkylamido, aroyl, benzoyl, alkyl C¿1?-C¿5? amino, dialkyl C¿1?-C¿5? amino, arylamino, diarylamino, aryl C¿1?-C¿5? alkylamino and cyclicamino groups, arylsulfinyl, arylsulfanyl, arylsulfonyl, linear or branched C¿1?-C¿10? alkylsulfonyl, P(O)(O-C¿1?-C¿10? alkyl)¿2? or is an alkenyl function of general formula (a) wherein R?11¿ and/or R?12¿ and/or R?13¿ is hydrogen or R?5¿, R?3¿, R?4¿, R?6¿, R?8¿ and R?10¿ are each hydrogen, R?1¿, R?2¿ or R?5¿; and R?7¿ and/or R?9¿ is hydrogen or an amino group provided that R?7¿ and R?9¿ are not both hydrogen. The compounds may be combined with a polymeric host material such as plastic or glass to make a sunglass lens, an ophthalmic lens or a window.