Synthesis and optical properties of naphthopyran dyes conjugated with fluorescent stilbazolium moieties

The synthesis of new 3H-naphtho[2,1-b]pyran dyes substituted at position 8 of the naphthalene ring by either a stilbazolium or an 4-ethenyl-quinolinium group and their photochemical properties are described. In non-polar media the naphthopyran-stilbazolium conjugates do not show any photochromic response while the formation of the ring opened species is promoted in strong polar media. Additional investigations of the new dyes within the pores of mesoporous MCM 41 particles showed a significant enhancement of the photochromism compared with that in solution. The generation of the ring-opened species upon irradiation with UV-light is accompanied by a decrease of the fluorescence intensity, which could be recovered by illumination with visible light.