Heterogeneous Transparent Ultrathin Films with Tunable‐Color Luminescence Based on the Assembly of Photoactive Organic Molecules and Layered Double Hydroxides

Abstract

Multicolor luminescent fi lms have great potential for use in optoelectronics, solid-state light-emitting materials, and optical devices. This work describes a systematic investigation of the ordered assembly of two-(blue/green, blue/ orange, red/blue, red/green) and three-color (blue/red/green) light-emitting ultrathin fi lms (UTFs) by using different photofunctional anions [bis( Nmethylacridinium)@polyvinylsulfonate ion pairs and anionic derivatives of poly( p -phenylene), poly(phenylenevinylene), and poly(thiophene)] and Mg-Al-layered double hydroxide nanosheets as building blocks. The rational combination of luminescent components affords precise control of the emission wavelengths and intensity, and multicolored luminescent UTFs can be precisely tailored covering most of the visible spectral region. The assembly process of the UTFs and their luminescence properties, as monitored by UV-vis absorption and fl uorescence spectroscopy, resulted in a gradual change in luminescence color in the selected light-emitting spectral region upon increasing the number of deposition cycles. X-ray diffraction demonstrates that the UTFs are periodic layered structures involving heterogeneous superlattices associated with individual photoactive anion-LDH units. These UTFs also exhibit well-defi ned multicolor polarized fl uorescence with high polarization anisotropy, and the emissive color changes with polarization direction. Therefore, this work provides a way of fabricating heterogeneous UTFs with tunablecolor luminescence as well as polarized multicolor emission, which have potential applications in the areas of light displays and optoelectronic devices.have been reported (semiconductor nanocrystals, [ 2 ] rare-earth compounds, [ 3 ] metal complexes, [ 4 ] and polymers [ 5 ] ), several challenges remain unresolved. Firstly, the differences in luminous effi ciency and intensity between different color components complicate the balance of the color display; as a result obtaining fi nely tunable luminescent colors is diffi cult and challenging. Secondly, a prerequisite for most optoelectronic applications is the development of transparent ordered fi lms; unfortunately, such fi lms have been much less frequently studied than solution and powder systems. [ 6 ] Thirdly, effi cient whitelight-emitting phosphors for substituting conventional light sources are rather limited, owing to the complicated synthesis procedures involved. [ 7a ] Additionally, the energy/charge transfer processes occurring between the different color components make it diffi cult to fi nely control the color purity and stability of the resulting white light. [ 7b ] Furthermore, although white-light emissions have been observed using both organic [ 7c ] and inorganic materials, [ 7d ] white-light materials with special performance, such as polarized emission, for instance, are still very rare; such materials need to be developed in order to solve the problems occurring in the backlighting of liquid-crystal displays. [ 8 ] Therefore, to meet the requireme...

Recent Advances in Stimuli‐Responsive Photofunctional Materials Based on Accommodation of Chromophore into Layered Double Hydroxide Nanogallery

“…Based on the difference in the emissive colors of the chromophores at different polarization direction, it is possible to develop a new type of color-switching materials upon stimuli by polarized light. Recently, we have fabricated four types of heterogeneous multicolor luminescent UTF materials (blue/red, blue/yellow, blue/green, and red/green emission) by using different photofunctional anions [bis(N-methylacridinium)@polyvi-nylsulfonate ion pairs and anionic derivatives of poly(pphenylene) (APPP), poly(phenylenevinylene) (APPV), and poly(thiophene) (APT)] and LDH nanosheets as building blocks [47]. The strategy for fabricating multicolor luminescent UTFs involves the stepwise assembly of individual luminescent species and LDH nanosheets.…”

Layer-by-layer assembly of ordered organic–inorganic luminescent film toward sensoring nitrobenzene compound

“…The approximately linear increase of the thickness upon increasing the bilayer number confirms that the TFs present uniform and periodic structure, in agreement with the behaviors revealed by the absorption and fluorescence spectra above. The uniform deposition can be assigned to the fact that the CXT and LDHs concentrations in the solution are much higher than that in the TF, although the concentration gradients changed in precursor solutions at different assembled cycles [25][26][27]. A typical top view of SEM image for the (CXT/LDH) 16 TF shows that the film surface is microscopically continuous and compact ( Fig.…”

Layered Double Hydroxide Materials: Assembly and Photofunctionality

“…However, the different luminous efficiency and intensity, complex fabrication process, as well as complicated interaction between these chromophores have severely limited the development of multicolor materials. Yan et al [77] have introduced LDH nanosheet as building block to combine different chromophores; in this case, materials with a rigid and ordered microenvironment, finely tuning emission color, and polarized multicolor luminescence can be achieved. Figure 42 shows the assembly process of multicolor emission materials employing APPP (blue) [76], APPV (orange) [78], SPT (red) [79], and BNMA (green) [95] as primary chromophores.…”

“…For the inorganic building blocks, quantum dots (QDs) [147] have attracted great attention due to high quantum yields, good stability, and high color purity [148], [77] and application of QDs in the multicolor emission materials has also been carefully investigated. Liang et al [117] have assembled QDs with LDH nanosheets to obtain highly ordered structure and finely tunable fluorescence, and the tunable color in the red-green region could be achieved by adjusting the assembly cycle number and sequence of red-and green-emission QDs.…”