© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2784 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com COMMUNICATION Yong Jun Li, Yongli Yan, Chuang Zhang, Yong Sheng Zhao,* and Jiannian Yao* Embedded Branch-Like Organic/Metal Nanowire Heterostructures: Liquid-Phase Synthesis, Efficient Photon- Plasmon Coupling, and Optical Signal Manipulation Y. J. Li, Prof. Dr. Y. Yan, C. Zhang, Y. S. Zhao, Prof. J. Yao Beijing National Laboratory for Molecular Sciences (BNLMS) CAS Key Laboratory of Photochemistry Institute of Chemistry Chinese Academy of Sciences, Beijing 100190, China Fax: ( +) 86-10-62652029 E-mail: yszhao@iccas.ac.cn; jnyao@iccas.ac.cn DOI: 10.1002/adma.201203829 Manipulation of photons at subwavelength scale is crucial for the realization of nanophotonic circuits for next-generation optical information processing. [1] Dielectric waveguides, fab- ricated from organic, [2] inorganic [3] and polymer materials, [4] exhibit low optical losses to control the flow of light, but optical confinement in these structures is restricted by the diffrac- tion limit. [5] A way of addressing this issue is to exploit surface plasmon polaritons (SPPs), which can spatially confine light in subwavelength metallic structures. [6–8] Unfortunately, the ohmic losses inhibit the transfer of optical signals across an entire circuit solely with plasmonic waveguides. [9,10] Hybrid sys- tems assembled from plasmonic and photonic nanowires could reduce the losses of the whole circuit. [11] More importantly, such wire-to-wire coupling scheme offers high efficiency for SPPs excitation in metal nanowires. [12] To date, most hybrid systems were fabricated by lithography [11] or micromanipulation, [12,13] however, these methods are either too complicated or unfit for the achievement of stable heterojunctions due to the simple point contact between the plasmonic and photonic nanowires. Recently, we have demonstrated that organic molecules can directly grow into nanowire heterojunctions via site-specific vapor phase growth. [14] By this strategy, organic/metal hybrid structures with stable connection between the organic and metal nanowires have been constructed. [15] In organic waveguides, the strong coupling between the Frenkel excitons and photons could form exciton polaritons (EPs). [16–19] The interactions between EPs and SPPs at the organic/metal junctions could bring new optical properties for the realization of nanophotonic devices. However, these hybrid structures have only one metal wire on each organic waveguide, which is difficult to realize multi-input and multi-output optical components. One possible solution is to synthesize the multi-branch heterostructures by molecular self-assembly in liquid phase. Organic molecules, especially the aromatic ones, can grow around and encapsulate the metal nanostructures, [20] which makes it possible to embed multiple metal nanowires in one organic waveguide. This method may allow for the fabrication of functional nanosystems and repre- sent significant advance to the “bottom-up” approach for nano- science and nanotechnology. [21] Here, we propose a novel approach to manipulating multiple optical signals at subwavelength scale based on efficient photon- plasmon coupling in dendritic organic/metal nanowire heter- ostructures. The heterostructures were prepared by embedding Ag nanowire branches in fac-tris(2-phenylpyridine) iridium (Ir(ppy) 3 ) microwire trunks during the self-assembly in liquid phase. The embedded Ag nanowires have different cross angles toward the Ir(ppy) 3 trunks, which have a great influence on the photon-plasmon coupling. At small coupling angle, the inten- sity of out-coupled light from the Ag tip is fairly strong, and the coupling efficiency decreases gradually with the increase of the cross angle. The multi-branch structures could serve as optical multiplexers with multiple input/output ports, where light sig- nals inputted from the organic waveguide could be selectively out-coupled to the predetermined subwavelength Ag nanowires. This coupling scheme may offer intensive understanding for the manipulation of optical signals and concepts for fabricating nanophotonic devices, [22,23] such as directional couplers, routers and logic gates. Ir(ppy) 3 (Figure S1) was chosen as the model compound because of its high luminescence efficiency and photolumi- nescence (PL) range. [24] The phosphorescence light of Ir(ppy) 3 makes it efficient to launch the SPPs of Ag nanowires because of the small momentum increment needed in the broad PL range (500–600 nm), as shown in Figure S2. [25] Chemically- synthesized Ag nanowires were utilized to support the SPPs because of their atomically smooth surfaces and reduced propagation losses. [26] The hybrid structures were prepared by embedding Ag nanowires in Ir(ppy) 3 microwires during the self-assembly in liquid phase (Figure S3). In a typical prepara- tion, the Ag nanowires were first synthesized with the previ- ously reported method. [27] The Ag nanowire solution (20 μL) in ethanol was added into 5 mL ethanol solvent. Then 400 μL of Ir(ppy) 3 solution in dichloromethane (1 mM) was rapidly injected into the above solution under continuous ultrasonica- tion. The rapid change of the surroundings induced the self- assembly of Ir(ppy) 3 molecules, and the Ag nanowires sus- pended in the solution were partially embedded in the organic microwires. Five hours later, the heterostructures with Ag nanowires embedded in the organic waveguides were finally obtained. The number of Ag branches could be controlled by changing the concentration of Ag nanowires in the ethanol solution. Adv. Mater. 2013, 25, 2784–2788