Dimeric Core–Shell Ag₂@TiO₂ Nanoparticles for Off-Resonance Raman Study of the TiO₂–N719 Interface

Abstract

In this paper, we present a nanoparticle-enhanced Raman spectroscopic study of TiO 2 -N719 (bis(tetrabutylammonium) [cis-di(thiocyanato)-bis (2, 2-bipyridyl-4-carboxylate-4-carboxylic acid)-ruthenium(II)])) interface by employing Ag 2 @TiO 2 dimeric core-shell nanoparticles, where the TiO 2 shell serves as an active semiconductor surface. The Ag 2 @TiO 2 nanoparticles are synthesized by connecting two Ag nanoparticles with thiol-modified complementary DNAs, followed by coating a 2 nm thin layer of TiO 2 on the Ag 2 dimeric nanoparticles. The Ag 2 @TiO 2 dimeric core-shell nanoparticles show red-shift of plasmon resonance frequency compared with Ag@TiO 2 core-shell nanoparticles, and provide significant SERS enhancement over the Ag@TiO 2 nanoparticles, which allows for the investigation of SERS of TiO 2 -N719 interface under off-resonance condition using low energy 785 nm laser excitation. Fine potential dependent Raman measurements show that thiocyano and carboxyl groups of the N719 molecule can adsorb on TiO 2 shell competitively: Along with negative potential excursion, the thiocyano is replaced by carboxyl, which is accompanied by conformation change of the molecule involving orientation change of the bipyridine ring. Furthermore, the potential of maximum intensity of the inter-ring vibration band shifts towards more positive value with laser excitation wavelength from 638 to 785 nm, which verifies the photon-driven charge transfer mechanism from the HOMO of N719 to the conduction bands of TiO 2 . Three-dimensional finite-difference time-domain (3D-FDTD) simulations are performed to evaluate the electromagnetic (EM) enhancement from the Ag 2 @TiO 2 dimeric core-shell nanoparticles. The present work demonstrates that the Ag 2 @TiO 2 dimeric core-shell structures provide significant plasmon resonance, which can be used for Raman investigations of interfaces formed with the semiconductor shell layers of the nanoparticles.

Core‐Shell Ag@TiO2 Nanocomposites for Low‐Power Blue Laser Enhanced Copper(I) Catalyzed Ullmann Coupling

“…The surface plasmon resonance (SPR) phenomenon is an interesting characteristic of metal nanoparticles (NPs). SPR is generated between the electric fields of incident electromagnetic waves and free electrons in metal NPs and this phenomenon has been exploited for surface enhanced spectroscopy, biological and chemical imaging, and lithographic fabrication . However, SPR enhancement of synthetic reactions using laser irradiation of noble metal nanoparticles has been limited to stoichiometric organic transformations and has never previously been used to enhance the catalytic reaction rate of C−C bond formation under homogeneous conditions.…”

DFT and TD-DFT Investigation of a Charge Transfer Surface Resonance Raman Model of N3 Dye Bound to a Small TiO2 Nanoparticle

“…Furthermore, some of the low-frequency modes in Table 3 of N719 excited with 632.8 on silver colloid in acetonitrile where strong adsorption via the NCS groups was proposed [13]. A Ag2@TiO2 dimeric-shell-core NP also shows the band at 2155 cm −1 for N719, again indicating it is adsorbed via the two NCS groups [16]. This peak for N719 moves to 2104 cm −1 on TiO2 surfaces [5,22,23] as we find with our simulation of complex A in which the two NCS groups are oriented away from the NP surface.…”

“…Various types of surface Raman studies of N3 or N719 dyes have also been made on Ag film substrates which contain TiO 2 layers, such as Ag@TiO 2 core shell NP structures where the dye is on the titania surface [15,16]. Excitation at 532 nm includes both an intramolecular resonance and the LSPR enhancement [15].…”

“…Potential-dependent studies indicate that NCS is interacting with the TiO 2 surface through the S atom. Also, the direct photoinduced CT from the Highest Occupied Molecular Orbital, HOMO, of N719 to the TiO 2 conduction band is indicated [16]. Bing Zhao and coworkers [17] investigated Ag/N719/ TiO 2 sandwich systems excited at 532, 633, and 785 nm with N719 adsorbed to Ag NPs via the isothiocyanate groups.…”

Graphene‐coated Au nanoparticle‐enhanced Raman spectroscopy

“…In addition, SHINERS is also a powerful and promising tool that can be applied in various fields, involving in surface science, materials, pharmaceutical analysis, biological medicine, food safety, and environmental protection. [ 23–26 ] Based on the shell‐isolated mode, there are a variety of shells that have been developed for SHINERS besides silica, including aluminum oxide, manganese oxide, titanium oxide, and carbon shell, which further broadens its application. [ 27–29 ] However, it is hard to obtain ultrathin and pinhole‐free shells, especially with shell thickness below 1 nm or on the atomic scale, which is of great significance to improve the detection sensitivity of surface‐adsorbed molecules.…”