Metallocenyl‐[2H]naphtho[1,2‐b]pyrans: metal effect on the photochromic behaviour

Previous studies have shown that the substitution by a ferrocenyl group in the 2‐position of naphthopyrans has a specific and an original effect on the photochromic behaviour. In this work, the synthesis and the photochromic properties of new naphthopyrans substituted in the 2‐position by three different metallocenyl groups (ferrocenyl, ruthenocenyl and osmocenyl) are presented. Whereas the ferrocenyl‐substituted derivatives under UV irradiation show two absorption bands, the ruthenocenyl and osmocenyl derivatives are characterized by only one absorption band under the same condition. The photochromic behaviour of these compounds is compared with that of their parent alkyl or phenyl 2‐substituted 2H]‐naphtho1,2‐b]pyrans. Copyright © 2002 John Wiley & Sons, Ltd.