No abstract

Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a technique for site-selective coupling of different materials to realize artificial high-efficiency devices. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS-Au-TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.

We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multi-fold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect that can be controlled by the metamaterial's design. This observation is an essential step towards understanding loss compensation in metamaterials with gain media and for developing metamaterial-enhanced gain media.Control of Joule losses is a key challenge for plasmonic and metamaterial technologies. Losses hamper the development of negative index media for super-resolution and optical cloaking devices, and plasmonic data processing circuits. Lowering losses is also crucially important for the performance of spectral filters, delay lines and, in fact, practically any other metamaterial and plasmonic applications [1]. Although using superconducting metamaterials can largely eliminate losses in THz and microwave metamaterials [2], Joule losses at optical frequencies are unavoidable. Recent works report compensation of losses with gain in metamaterials aggregated with semiconductor quantum dots (QDs) [3] and organic dyes [4] embedded into the metal nanostructures. Parametric metamaterials gain systems are also under investigation in theory [5][6][7]. Another grand goal of active metamaterials research is to improve laser gain media and to develop a 'lasing spaser' device: a 'flat' laser with emission fueled by plasmonic excitations in an array of coherently emitting meta-molecules [8]. An essential part of this development shall be the study of luminescence of active material hybridized with plasmonic nanostructures that could support collective, coherent plasmonic excitations in the lasing spaser. Here we report the first study of photoluminescence of semiconductor QDs hybridized with asymmetric split-ring plasmonic metamaterial. This type of metamaterial supports a closed-mode Fano-type excitation which has the key characteristics required for the lasing spaser application: the mode is formed by collective interactions between individual meta-molecules that shall ensure coherent laser action [9]. In this letter, we experimentally demonstrate that the photoluminescence properties of QDs can be greatly enhanced by the plasmonic metamaterial. Figure 1(a) schematically illustrates a plasmonic metamaterial combined with QDs. The metamaterials studied here consist of periodic arrays of asymmetrically split ring slits (negative structure), which have been successfully applied to switching, nonlinear and sensor applications [10]. The metamaterial arrays with a total size of 40 × 40 µm each were fabricated by focused ion beam milling in a 50nm-thick gold film on a glass substrate [see inset of Fig. 1(b)]. In order to systematically investigate the correlation between QD photoluminescence spectrum and the spectral position of the Fano plasmonic metamaterial resonance, we manufactured five metamaterial arrays with different unit cell sizes rangin...

A series of copper(II) complexes with tripodal polypyridylmethylamine ligands, such as tris(2-pyridylmethyl)amine (tpa), ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine (Me(1)tpa), bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me(2)tpa), and tris((6-methyl-2-pyridyl)methyl)amine (Me(3)tpa), have been synthesized and characterized by X-ray crystallography. [Cu(H(2)O)(tpa)](ClO(4))(2) (1) crystallized in the monoclinic system, space group P2(1)/a, with a = 15.029(7) Å, b = 9.268(2) Å, c = 17.948(5) Å, beta = 113.80(3) degrees, and Z = 4 (R = 0.061, R(w) = 0.059). [CuCl(Me(1)tpa)]ClO(4) (2) crystallized in the triclinic system, space group P&onemacr;, with a = 13.617(4) Å, b = 14.532(4) Å, c = 12.357(4) Å, alpha = 106.01(3) degrees, beta = 111.96(2) degrees, gamma = 71.61(2) degrees, and Z = 4 (R = 0.054, R(w) = 0.037). [CuCl(Me(2)tpa)]ClO(4) (3) crystallized in the monoclinic system, space group P2(1)/n, with a = 19.650(4) Å, b = 13.528(4) Å, c = 8.55(1) Å, beta = 101.51(5) degrees, and Z = 4 (R = 0.071, R(w) = 0.050). [CuCl(Me(3)tpa)][CuCl(2)(Me(3)tpa)]ClO(4) (4) crystallized in the monoclinic system, space group P2(1)/a, with a = 15.698(6) Å, b = 14.687(7) Å, c = 19.475(4) Å, beta = 97.13(2) degrees, and Z = 4 (R = 0.054, R(w) = 0.038). All the Cu atoms of 1-4 have pentacoordinate geometries with three pyridyl and one tertiary amino nitrogen atoms, and a chloride or aqua oxygen atom. Nitrite ion coordinated to the Cu(II) center of Me(1)tpa, Me(2)tpa, and Me(3)tpa complexes with only oxygen atom to form nitrito adducts. The cyclic voltammograms of [Cu(H(2)O)(Me(n)()tpa)](2+) (n = 0, 1, 2, and 3) in the presence of NO(2)(-) in H(2)O (pH 7.0) revealed that the catalytic activity for the reduction of NO(2)(-) increases in the order Me(3)tpa << Me(2)tpa << Me(1)tpa < tpa complexes.