Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators

Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators1, 2, 3, 4, 5, 6, 7. The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy8, 9, 10, 11 between λ0 = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10−8λ03. By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters12. Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.Peer ReviewedPostprint (author's final draft

Selectivity of a thiosemicarbazonatocopper(II) complex towards duplex RNA. Relevant noncovalent interactions both in solid state and solution

Thiosemicarbazones and their metal derivatives have long been screened as antitumor agents, and their interactions with DNA have been analysed. Herein, we describe the synthesis and characterization of compounds containing [CuL]+ entities (HL = pyridine-2-carbaldehyde thiosemicarbazone) and adenine, cytosine or 9-methylguanine, and some of their corresponding nucleotides. For the first time, crystal structures of adenine- and 9-methylguanine-containing thiosemicarbazone complexes are reported. To the best of our knowledge, the first study on the affinity thiosemicarbazone–RNA is also provided here. Experimental and computational studies have shown that [CuL(OH2)]+ entities at low concentration intercalate into dsRNA poly(rA)·poly(rU) through strong hydrogen bonds involving uracil residues and π–π stacking interactions. In fact, noncovalent interactions are present both in the solid state and in solution. This behaviour diverges from that observed with DNA duplexes and creates an optimistic outlook in achieving selective binding to RNA for subsequent possible medical applications.Obra Social “la Caixa” (OSLC-2012-007), Ministerio de Economía y Competitividad and FEDER funds (CTQ2013-48937-C2-1-P, CTQ2015-70371- REDT, MAT2012-34740 and CTQ2014-58812-C2-2-R), Junta de Castilla y León (BU237U13), the Basque Government (IT-779- 13), Gerencia Regional de Salud, Consejería de Sanidad, Junta de Castilla y León (GRS 1023/A/14 and GR172)

Synthesis and Structure of Four-Coordinate Copper(II) Complexes Stabilized by β-Ketiminato Ligands and Application in the Reverse Atom-Transfer Radical Polymerization of Styrene

International audienceThe reaction of CuCl2 with R2NCH2CH2NHC(Me)=CHCO(Me) [R = Me (HL1) or Et (HL2)] in the presence of Et3N leads to the formation of complexes [CuCl(Ln)] [n = 1 (1), 2 (2)]. Whereas the solid‐state structure of compound 2 is mononuclear with a close to square‐planar arrangement of the ClON2 donor set, compound 1 adopts a dinuclear di‐μ‐chlorido arrangement in which two mononuclear units having essentially the same arrangement as in 2 establish loose axial Cu···Cl interactions, each one of them with the Cl atom of the other one. Compounds 1 and 2 have been tested as reversible trapping agents for the controlled radical polymerization of styrene under a reverse atom‐transfer radical polymerization (ATRP) approach. Reversible Cl atom transfer leading to a controlled polymerization process is observed, although the controllability is negatively affected by slow radical trapping. A moderate effect on the polymerization rate, once all the radical initiator is consumed, was observed in the presence of an excess amount of pyridine (10 equiv. per Cu) and interpreted on the basis of the stabilization of the CuI system