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Layer-by-layer assembly of ruthenium(II) complex anion/layered double hydroxide ordered ultrathin films with polarized luminescencew
| Content Provider | Semantic Scholar |
|---|---|
| Author | Yan, Dongpeng Wei, Maojie Ma, Jing Evans, David G. Duan, Xue Chen |
| Copyright Year | 2009 |
| Abstract | Transition-metal-based photoactive complexes (PC) have received a great deal of attention during the last two decades, because their chemical stability and excellent luminescence properties give rise to many possible applications in optoelectronics. Ruthenium-based complexes that feature a metal-to-ligand charge transfer (MLCT) transition mechanism are an important class of such materials, and they have been extensively investigated in solid-state phosphorescent light-emitting devices and electrochemical cells. Generally, oriented photoemissive structures, such as one-dimensional luminescent polymers, show well-polarized luminescence character which can be employed in liquid-crystal displays. However, except for the recent work of Galyametdinov, very little attention has been focused on the polarized luminescence characteristics of PC materials, owing to the highly symmetric structure and low luminescence anisotropy of most of these complexes, e.g. the 8-hydroxyquinoline aluminium complex exhibits no polarized emission due to its pseudo-spherical structure. It is therefore desirable to find ways to develop PC materials with polarized luminescence performance in order to incorporate the advantages of such materials in the next generation of optoelectronic devices. Layered double hydroxides (LDHs) are a class of naturally occurring and synthetic materials, which can be described by the general formula [M1 xM III x(OH)2] (A )z/n yH2O, whereM andM are divalent and trivalent metals respectively and A is the anion which compensates for the positive charges of the metal hydroxide layers. LDHs can be exfoliated into positively charged monolayers and assembled in alternation with polyanions via a layer-by-layer (LBL) technique, resulting in novel ultrathin films (UTFs). To the best of our knowledge, however, the assembly of LDH monolayers and small anions has never been reported. This restricts the available range of LDH-based organic–inorganic hybrid functional UTF materials. Moreover, fabrication of an ordered assembly of such luminescent anions with the layered host structure may offer a new method for constructing films with polarized photoemission, since it should be possible to obtain a uniform and ordered orientation of the guest anions within the rigid LDH matrix. Herein, we demonstrate the fabrication of ordered stacked UTFs, based on a small anionic PC and LDH monolayers as building blocks, by the LBL method. The highly symmetric anion (D3 point group), tris(1,10-phenanthroline-4,7-diphenylsulfonate)ruthenium(II) ([Ru(dpds)3] 4 , Scheme 1a), which has been reported to have the highest photoluminescence quantum yield (36%) of all ruthenium complexes, was chosen as the light-emitting complex to be assembled with exfoliated Mg-Al-LDH monolayers (Scheme 1b). The multilayer assembly process (Scheme 1c) of the (Ru(dpds)3/LDH)n (n = 4–32) UTFs deposited on quartz substrates was monitored by UV-visible absorption spectroscopy (Fig. 1a). The intensities of the absorption bands at 196, 287 and 471 nm (resulting from a E1u transition, a p–p* transition, and an MLCT transition of [Ru(dpds)3] 4 , respectively) correlate nearly linearly with the number of bilayers n (Fig. 1a, inset), indicative of a stepwise and regular deposition procedure with almost equal amounts of [Ru(dpds)3] 4 incorporated in each cycle. This was confirmed by the gradual increase in the color intensity of the UTFs with increasing number of bilayers (Fig. 1c). The intensity of the sharp luminescence peak with a maximum at ca. 615 nm of the (Ru(dpds)3/LDH)n UTFs also displays a monotonic increase with n, as shown in Fig. 1b. The luminescence wavelength of |
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| Alternate Webpage(s) | http://www.ldh-buct.com/wp-content/uploads/2015/03/2009-8.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
