Elsevier

Materials Letters

Volume 153, 15 August 2015, Pages 40-43
Materials Letters

Layer-by-layer assembly of luminescent multilayer thin films by MMT, anionic chromophores and magnetic CoAl-LDHs nanosheets

https://doi.org/10.1016/j.matlet.2015.04.002Get rights and content

highlights

  • Transition metal-bearing layered double hydroxides provide magnetic field (MF).

  • A novel electronic microenvironment (EME) is successfully designed.

  • The EME is assembled by oppositely-charged inorganic nanosheets.

  • Chromophores are successfully designed in EME and MF between the interlayer.

  • Lifetimes of chromophores with EME and MF are highly prolonged.

Abstract

In this report, luminescent multilayer thin films (MTFs) based on oppositely-charged montmorillonite (MMT) and transition metal-bearing layered double hydroxides (LDHs) nanosheets were fabricated via a layer-by-layer assembly method. Oppositely-charged inorganic nanosheets can be expected to assemble an electronic microenvironment (EME), and transition metal-bearing LDHs nanosheets can offer an additional magnetic field (MF) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of MTFs with EME and MF are significantly prolonged compared with that of the pristine chromophores, even much longer than those of MTFs without oppositely-charged and magnetic architecture. Therefore, it is highly expected that the EME and MF formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on enhancing the luminescent lifetimes of chromophores, which suggest a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices at molecular level.

Introduction

Layered materials are attractive targets for their rich fundamental physics and potential applications in future multifunctional devices, and the nanosheets of those have been used as building units for making new designed nanomaterials due to their intrinsic unique two-dimensional structure [1], [2], [3], [4]. As for LDHs and MMT, several groups have just done many profound researches by using naonosheets with two-dimensional arrays which can provide a rigid and stable environment [5], [6], [7], [8], [9], [10]. However, various different inorganic nanosheets possibly have certain natural features, such as LDHs exhibit permanent positive charge and MMT׳ nanosheets are evolved as permanent negative charge that can be delocalized over the entire layer surface, due to an isomorphic substitution [10], [11]. But there was no relational report about taking full advantage of the nanosheets׳ charge, until our group [12] successfully confirmed that electronic microenvironment, which is assembled by oppositely-charged nanosheets between the interlayer, is fairly beneficial for enhancing the lifetimes of MTFs containing luminescent cations. On the other hand, transition metal-bearing LDHs׳ nanosheets can act as nanoscale ferromagnetic layers, and their multilayer assemblies exhibit significant magneto-optical response [9], [10], [13]. And then, our present work confirmed that MF also can improve the optical property in coordination with EME, especially the lifetimes of MTFs [14]. Herein, in this paper, what we are most interested in are whether anionic luminescent polymers can be designed for intercalating into EME and MF environments, and whether they can be affected by the different ferromagnetic inorganic nanosheets on the optical properties.

In this work, a luminescent π-conjugated anionic polymer poly [5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] potassium (APPV) was assembled with the CoAl-LDHs nanosheets and MMT nanosheets to fabricate multilayer thin films (MTFs), respectively. In the nano-system, as the assembled nano-architecture can provide an EME and the CoAl-LDHs can offer a constant MF to the chromophores (Fig. 1), the MTFs exhibit remarkable optical properties with reasonably longer luminescent lifetimes. Herein, this work successfully fabricates the MTFs with EME and MF′, which can promote the hybrid systems with various functions, and confirm the concept about the EME and MF effecting chromophores simultaneously.

Section snippets

Results and discussion

We selected the luminescent π-conjugated anionic polymer to assemble with different ferromagnetic inorganic nanosheets, in order to confirm the universality of the novel concept about EME and MF effecting the more series chromophores. The UV–visible absorption spectra of (CoAl-LDHs/APPV@PVA)n MTFs with varying numbers of assembly steps are shown in Fig. 2a, and the intensity of absorption peaks exhibit correlate linearly with the deposition cycles (Fig. 2a, inset), demonstrating a stepwise and

Conclusions

To sum up, this work successfully confined anionic chromophores in the oppositely-charged and magnetic inorganic layer hosts. Importantly, it successfully demonstrates that the EME and MF formed by the different ferromagnetic inorganic nanosheets are fairly beneficial for enhancing the luminescent lifetimes of MTFs containing anionic chromophores. Therefore, the as-fabricated MTFs are expected to have much flexibility and be potential for manipulating, controlling and developing novel

Acknowledgments

This work was supported partially by the National Natural Science Foundation of China (Grant no. 40802013), Key Projects in the National Science & Technology Pillar Program (Grant no. 2006BAD10B04), the Fundamental Research Funds for the Central Universities (Grant no. 2011YXL058).

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