Article pubs.acs.org/JACS
Supramolecular Self-Assembly and Dual-Switch Vapochromic, Vapoluminescent, and Resistive Memory Behaviors of Amphiphilic Platinum(II) Complexes Yongguang Li,*,†,§ Ling Chen,†,§ Yeye Ai,† Eugene Yau-Hin Hong,‡ Alan Kwun-Wa Chan,‡ and Vivian Wing-Wah Yam*,†,‡ †
Lehn Institute of Functional Materials, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, P. R. China Institute of Molecular Functional Materials [Areas of Excellence Scheme, University Grants Committee (Hong Kong)] and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China
‡
S Supporting Information *
ABSTRACT: A series of amphiphilic platinum(II) complexes with tridentate N-donor ligands has been synthesized and characterized. Different supramolecular architectures are constructed using the amphiphilic molecules as the building blocks through the formation of Pt···Pt and π−π stacking interactions in aqueous media. The aggregation−deaggregation−aggregation self-assembly behavior together with obvious spectroscopic changes could be fine-tuned by the addition of THF in aqueous media. More interestingly, one of the complexes is found to show fast response and high selectivity toward alcohol and water vapors with good reversibility, leading to drastic color and luminescence changes, and hence unique dual switching behavior, with the water molecules readily displaced by the alcohol vapor. Rapid writing and erasure have been realized via the control of a jet or a stream of alcohol vapor flow. In addition, it has been employed as active materials in the fabrication of small-molecule solution-processable resistive memory devices, exhibiting stable and promising binary memory performance with threshold voltages of ca. 3.4 V, high ON/OFF ratios of up to 105 and long retention times of over 104 s. The vapochromic and vapoluminescent materials are demonstrated to have potential applications in chemosensing, logic gates, VOC monitoring, and memory functions.
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INTRODUCTION Luminescent platinum(II) complexes have been explored to construct supramolecular architectures due to their tendency to form metal−metal and π−π stacking interactions.1−7 Intriguing spectroscopic and rich luminescent properties are found to emerge during the self-assembly process through a delicate balance of non-covalent interactions such as metal−metal, π−π stacking, hydrogen-bonding, and electrostatic interactions. Color changes monitored by naked eyes or spectral changes could be observed through a judicious choice of solvent compositions or counter-anions, changes in pH, the addition of polyelectrolytes, and so on.8−19 Recently, platinum(II) complexes with terpyridine (tpy) and 2,6-bis(benzimidazol-2′yl)pyridine (bzimpy) ligands were reported to show a variety of interesting vapochromic, metallogel, and aggregation properties as a result of metal−metal and π−π stacking interactions.3,4,8−15 In particular, the alteration of metal−metal and π−π stacking interactions in the solid state upon the adsorption of vapors of volatile organic compounds (VOCs) would lead to rich vapochromic and vapoluminescent properties that are attractive for the development of chemosensors.20−24 However, the slow response and complicated procedures for the activation/ © 2017 American Chemical Society
recovery processes of a number of vapochromic systems of platinum(II) complexes, together with the rather poor selectivity and reproducibility, have limited their practical applications.21−28 As a result, it is important to develop highly sensitive materials with good selectivity to specific species, fast response, good reversibility, and easy device fabrication.29−32 Motivated by the exploration of selective and sensitive vapochromic and vapoluminescent materials, we are interested in the design of amphiphilic platinum(II) complexes with 2,6bis(1-propanesulfonate-1,2,3-triazol-4-yl)pyridine (btapy) ligands and the study of their vapochromic, vapoluminescent, and self-assembly properties (Scheme 1). Remarkably, one of them (1-PPN) is found to display drastic color and luminescence changes upon the switchable adsorption between alcohol and water vapor, which renders the complex useful in the detection of alcohol vapors. Additionally, the color changes occur rapidly (violet → orange) once it is exposed to damp air or water vapor. The orange form with H2O molecules adsorbed can respond instantaneously upon exposure to alcohol vapors, Received: July 21, 2017 Published: September 21, 2017 13858
DOI: 10.1021/jacs.7b07638 J. Am. Chem. Soc. 2017, 139, 13858−13866
Article
Journal of the American Chemical Society Scheme 1. Structures of the Platinum(II) Complexes
without the need for pre-baking or evacuation to remove the adsorbed water (Supporting Videos 1 and 2). Rapid writing− erasure processes have also been realized on the film prepared from the vapochromic material via the control of a jet or a stream of alcohol vapor flow (Supporting Video 3).33,34 Such reversible uptake and dramatic color changes as a result of changes in metal−metal and π−π stacking interactions upon the adsorption of alcohol or water vapor suggest that 1-PPN is a promising candidate for potential applications as luminescent probes to monitor alcohol and humidity. The reversible color switching properties may also pave the way for potential development of these complexes as memory storage materials in response to external stimuli. In light of this scenario and our continuing interest in small-molecule organic resistive memories,35−42 this class of platinum(II) complexes has been found to show binary memory behavior and is envisaged to be a promising candidate for the exploration of their memory applications in addition to their intriguing vapochromic and vapoluminescent functions.
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Table 1. Photophysical Data of the Complexes complex 1-PPN
medium (T/K) CH3OH (298)
λmax /nm (εmax/ dm3 mol−1 cm−1)
λem/nm (τo/μs)
278 sh (23095), 324 (6390), 358 (4015), 377 sh (2395)
615 (
