Multifunctional photochromic spiropyran dendrimers and their relaxation behaviors of photochromism

First and second generation dendrimers that exhibit unique photochromic behavior were synthesized through multi-step reactions. Their photochromic behavior under illumination of monochromatic ultraviolet light (λ = 365 nm) was investigated. The colorless dendritic dye solution and its film exhibit typical ring opening and E/Z geometrical transformation from spiropyran to merocyanine. The stability of photochromism in the two dendrimers was much better than that observed in the dye-attached polymer or dye-doped polymer system. Particularly, blend material system of photochromic dendrimer and photocrosslinkable dendrimer showed much better stability of the photochromism.     

Spectrum-stable hyperbranched polyfluorene with photocrosslinkable group

Two kinds of blue light-emitting hyperbranched crosslinkable polyfluorene P1 and P2 with different contents of branch unit were synthesized via the palladium-catalyzed Suzuki coupling reaction, and the linear crosslinkable polyfluorene P0 was also prepared for comparison. The molecular weight and thermal behavior of the polymers were measured by GPC, DSC and TGA. Compared with uncrosslinked P0, P1 and P2, the photoluminescence spectra of crosslinked P0, P1 and P2 were little influenced. After annealing for 3 h at 200 °C in air, the photoluminescence spectrum of P2 with higher contents of branch unit showed more excellent stability compared with that of P1 and P0. The spectrum-stable hyperbranched polyfluorene can be used in multilayer and multicolor PLED.