Two-color polarized emission and angle-dependent luminescence based on layer-by-layer assembly of binary chromophores/layered double hydroxide thin films

The polarized and angle-dependent luminescent films have great potential for use in new types of optical display materials and fluorescent antiforgery devices. In this work, we report the layer-by-layer co-assembly of two types of two-color (blue/red) luminescent ultrathin films (UTFs) by using different photofunctional anions (optical brightener VBL, sulfonated poly(thiophene), and tris(1,10-phenanthroline-4,7-diphenylsulfonate) ruthenium(II)) and Mg-Al-layered double hydroxide (LDH) nanosheets as the basic building blocks. UV-visible absorption and fluorescence spectroscopy showed an orderly growth of the two types of UTFs upon increasing the number of deposition cycles. XRD and SEM measurements indicated that the films feature periodic layered structure as well as uniform surface morphology. Moreover, these UTFs can exhibit well-defined two-color polarized fluorescence with high polarization anisotropy. In addition, changeable ratiometric luminescence can also be obtained at different viewing angles. Therefore, this work provides a facile way of fabricating two-color UTFs which have potential applications in the areas of both polarized multi-color emission and angle-dependent luminescent materials.