Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Abstract

Measurement and interpretation of the excitation wavelength dependence of surface-enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445-780-nm range and factor analysis (FA) were used for the identification of two Ag-2,2′:6′,2″-terpyridine (tpy) surface species, denoted Ag + -tpy and Ag(0)-tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride-reduced hydrosols. Ag + -tpy is a spectral analogue of [Ag(tpy)] + complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)-tpy surface complex generated upon chlorideinduced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ exc = 532 nm) and off-resonance (λ exc = 780 nm) pure-component spectra of Ag(0)-tpy obtained by FA are largely similar to surface-enhanced resonance Raman scattering (λ exc = 532 nm in resonance with singlet metal to ligand CT ( 1 MLCT) transition) and SERS (λ exc = 780 nm) spectra of [Fe(tpy) 2 ] 2+ complex dication.

Recent advances in linear and non‐linear Raman spectroscopy. Part X

“…Sloufova et al . have identified two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis which provides evidence for the chemical mechanism contribution to SERS of Ag(0)‐tpy …”

SERS microRaman spectral probing of adsorbate-containing, liquid-overlayed nanosponge Ag aggregates assembled from fractal aggregates

“…The signal increase was attributed to a combined effect of ion pair formation and Ag NP aggregation . Interestingly, the simple modification of HA‐Ag NP hydrosols by addition of chlorides was not sufficient for generation of Ag(0)‐2,2′:6′,2″‐terpyridine (tpy) surface complex, although a more complex synthetic approach involving addition of chlorides to a two‐phase water–dichloromethane system led to an efficient formation of this particular surface complex and confirmed thus the presence of Ag(0) adsorption sites on Ag NP surfaces in nanoparticulate films and aggregates deposited from these systems …”