Metal nanostructures with localized surface plasmon resonance (LSPR) have attracted great attention in catalysis, sensing, nanooptics, and nanomedicine. Charge transfer plasmon (CTP) is a LSPR mode that strongly depends on a conductive junction between metallic nanounits. Benefitting from the charge transfer junction, CTP provides a facile way to generate widely tunable LSPR with highly localized/enhanced light magnetic field and photothermal effect. The limited availability of highly tunable CTP structures and their fabrication techniques hinders a further pursuit of their functions and applications. In response to this situation, the present work aims at developing a simple while highly efficient synthetic route to width-adjustable Au/Cu heterojunctions capable of evoking tunable CTP behaviors. The strategy relies on a non-specific surface adsorption of low-cost, naturally occurred fish sperm DNA on a gold nanoseed to control heterogeneous copper nucleation. Such a process offers a chance to tailor the contact area between the gold and copper nano-domains in the bimetallic structure. Highly tunable CTP resonance from visible to near-infrared region is then realizable on the basis of this method. Experimental and calculated extinction spectra consistently reveal three key variables for the CTP structure, including the width of conductive junction and the sizes of gold and copper particles. These parameters are associated with DNA coverage, copper precursor concentration, and the synthetic conditions for gold nanoparticles, which allow for a CTP tuning from visible to near infrared wavelengths. By fully exploiting these highly controllable parameters, the maximally achievable CTP wavelength readily enters a near infrared II domain. The resulting CTP signals have a red-shift of up to 750 nm relative to the 530~570 nm LSPR peaks of individual gold and copper nanoparticles, corresponding to a very narrow Au/Cu conductive contact of 11~13 nm in width. The role of nonspecific DNA adsorption in the above process proves unique (currently irreplaceable) compared to other molecular adsorbates. The easily tunable Au/Cu heterointerface paves a way to integrated CTP and catalytic/sensing functions in future research.
The mechanisms of the electron transfer of S-benzyl-N-(ferrocenyl-1-methyl-methylidene)-dithiocarbazate palladium(II)/zinc(II) complexes [Pd(lsb)2]/[Zn(lsb)2] were studied by cyclic voltammetry, differential pulse voltammetry, digital simulation and in-situ subtractively normalized interfacial Fourier transform infrared (SNIFTIR) spectroelectrochemistry. The results indicate that [Pd(lsb)2], which has a square-planar configuration, involved two consecutive one-electron steps in the redox process, while the tetrahedral configuration of Zn(II) involved a two-electron step. The [Pd(lsb)2] complex exhibits a moderately strong electronic communication between the two-ferrocene moieties, which occurs through the skeleton chain of the ligand due to extensive electron delocalization of the whole molecule during the redox process, while the [Zn(lsb)2] complex shows low electron delocalization, and has two almost identical ferrocene moieties.
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