Evidence for SERRS Enhancement in the Spectra of Ruthenium Dye–Metal Nanoparticle Conjugates

Abstract

Metal−molecule interfaces have a high potential for applications in various fields of chemistry, as the features and functions of metal nanostructures can be modified and, to a certain degree, extended by surface-bound molecules. In this article, the functionalization of complex colloidal particles, namely, Au nanopeanuts and Au/Pt/Au nanoraspberries, with the commercially available Ru complexes N719, N749, and Z907 is reported; these Ru complexes have already been applied as photosensitizers in dye-sensitized solar cells. A detailed investigation of the conjugates by means of Raman spectroscopy showed that the electronic structures of the ruthenium complexes are retained upon binding to the metal nanoparticles. Furthermore, microfluidics as an efficient tool for the systematic investigations of SER(R)S signal-enhancement dispersion in colloidal solutions was applied. The enhancement profiles obtained differed from the extinction spectra of the nanoparticles, indicating that electronically resonant processes are involved in the Raman signal enhancement of the investigated nanoparticle conjugates, in addition to the Raman signal enhancement due to the SERS effect.

The SERS effect in coordination chemistry

“…This system is particularly interesting, since it illustrates the occurrence of SERRS effect in stabilized nanoparticles, under no influence of aggregation, exposing the role of the surface plasmon resonance in promoting a further enhancement of the molecular resonance Raman mechanism. A similar report has also been published by Theil et al [272] for as series of thiocyanateruthenium-carboxybipyridine dyes commercially available as N719, N749 and Z907, anchored on gold nanopeanuts and Au/Pt/Au nanoraspberries.…”

Comparison of SERRS and RRS excitation profiles of [Fe(tpy)2]2+(tpy = 2,2':6',2''‐terpyridine) supported by DFT calculations: effect of the electrostatic bonding to chloride‐modified Ag nanoparticles on its vibrational and electronic structure

“…For several types of electrostatically bonded chromophores, e.g. metalloporphyrins, antibiotics, dyes, and transition metal complexes, the SERRS and the RRS spectra excited at the same excitation wavelength have shown nearly identical wavenumbers of spectral bands indicating preservation of the molecular structure. On the other hand, changes in relative band intensities attributed to ion pairing were reported, e.g.…”

“…Metal complexes represent an important class of chromophores well suited for investigation of the effect of surface‐adsorbate bonding in SERRS . Nevertheless, their successful employment as model chromophores for this purpose is conditioned by a reliable assignment of their RRS spectra and electronic transitions in the free (nonadsorbed) state.…”

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

“…To study the interfacial interactions which govern the adsorption configuration of molecules and thus affect the efficiency of charge transfer across the interface, spectroscopic techniques such as infrared [2][3][4][5][6][7] and Raman spectroscopies 1,4,6,[8][9][10][11] serve as powerful tools as they can provide finger print information about interfacial interactions with adsorbed species. In general, to study surface process, enhancement of Raman signals is an important issue and most effectively attained using the effect of localized surface plasmon resonance (LSPR) created from metal nanoparticles (NPs) onto which molecules are adsorbed [12][13][14][15][16] .…”