Absorption Spectra of Xanthone and Dibenzoxanthones

Abdel-Kerim, F. M.; Shoeb, H. A.

doi:10.1515/zpch-1972-0123

Cited by 2 publications

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“…Table 1 shows the assignment of the main bands in the R6G SERS spectrum. 28,[38][39][40] The four bands that are relatively stable in our spectral trajectories are seen to be due to in-plane stretch vibrations, while the two fluctuating bands involve bend vibrations. This is a qualitative difference that might indicate the disparity in the behavior of the two groups.…”

Section: Discussionmentioning

confidence: 99%

Time-Dependent Single-Molecule Raman Scattering as a Probe of Surface Dynamics

2001

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Large spectral fluctuations, on a time scale of many seconds, are demonstrated in the surface-enhanced Raman scattering of single rhodamine 6G molecules adsorbed on silver nanocrystals and excited at 532 nm. These fluctuations are especially evident in the case of the vibrational bands at 614 and 774 cm -1 . A definite connection between spectral fluctuations and changes in the shape of the diffuse background emitted with the SERS spectrum is seen, pointing to the possible origin of both in a molecule-surface charge transfer phenomenon. The rate of spectral fluctuations is shown to depend linearly on laser intensity through a nonthermal mechanism. The rate of fluctuations can also be modified by changing the anion concentration in the solution on top of the silver colloids. Analysis of the results suggests that the fluctuations are due to motion of the adsorbed molecule on the surface, triggered by photodesorption events that are mediated by electron tunneling between the molecule and surface. Our results show that single-molecule Raman scattering can serve as a sensitive local probe for the dynamics of adsorbed molecules under ambient conditions.

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Section: Discussionmentioning

confidence: 99%

Time-Dependent Single-Molecule Raman Scattering as a Probe of Surface Dynamics

2001

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“…While the mechanism by which the LWF changes at the adsorption site of a molecule is not clear yet, and can be attributed to molecular diffusion but also to surface dynamics, we can still build a simple model that will allow us to translate spectral fluctuations to LWF fluctuations. To do this, we focus here on spectral changes in one vibrational band of R6G, the C-C ring in-plane bend at 614 cm -1 [35][36][37] , and calculate the ratio of the time-dependent intensity of this band to the intensity of one of the bands that do not show strong fluctuations, the aromatic C -C stretch at 1650 cm -1 . This ratio, as obtained from one molecule, is plotted in Figure 4A.…”

Section: Spectral Fluctuations and The Lwf Distributionmentioning

confidence: 99%

Single molecule raman spectroscopy and local work function fluctuations

Haran

2004

Israel Journal of Chemistry

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Single molecule Raman spectroscopy provides information on individual molecules with vibrational-level resolution. The unique mechanisms leading to the huge Raman cross-section enhancement necessary for single molecule sensitivity are under intense investigation in several laboratories. We recently analyzed large spectral fluctuations in single molecule spectra of rhodamine 6G on silver surfaces (A. Weiss and G. Haran, J. Phys. Chem. B (2001), 105, 12348-12354). The appearance of the fluctuations in two particular vibrational bands, and their dependence on several parameters, suggested that they originate in a charge transfer interaction of an adsorbed molecule with the surface. We argued that the fluctuations are due to variations of the local work function at the position of the molecule. In the current paper the fluctuations are further analyzed in terms of the intensity ratio between a fluctuating and a quiescent band, and it is found that the distribution of this ratio is independent of laser power, unlike the correlation time of the fluctuations. Weshow that a simple model, based on the energetics of charge transfer, can be used to extract the local work function distribution from the intensity ratio distribution. In a second experiment, single molecule spectra are collected from colloids immersed in water and in glycerol and a threefold decrease in fluctuation rate is found in the more viscous fluid. This indicates that surface dynamics are indeed responsible for the fluctuations, involving the motion of the adsorbed molecule and possibly also that of surface silver atoms around it. _______________________________________________________ 3 The spectroscopy of single molecules opens up new opportunities for the analysis of molecular dynamics. Much of the single molecule spectroscopy field is involved with fluorescence measurements. However, fluorescence is limited as a source of spectroscopic information on molecules, especially at room temperatures, where fluorescence spectral lines are broad and featureless. Thus, Raman spectroscopy is a very welcome addition to the arsenal of methods aimed at studying individual molecules. The large scattering cross section required for the detection of Raman signals from single molecules is attained through surface enhancement. A judicious application of this technique must rely on a thorough understanding of the mechanism of this enhancement. Surprisingly, even after more than 25 years of intense research into the phenomenon of surface-enhanced Raman scattering (SERS), many basic questions still remain unexplained. In fact, single molecule studies might reflect back on the SERS field by teaching us new facts and providing fresh explanations. This paper is opened with a discussion of current thinking on the microscopic processes leading to the huge scattering enhancement observed in single molecule Raman measurements. Our own recent work, in which we studied fluctuations in Raman spectra of individual rhodamine 6G (R6G) molecules on silver colloidal nanoparticles, is re...

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Absorption Spectra of Xanthone and Dibenzoxanthones

Cited by 2 publications

References 0 publications

Time-Dependent Single-Molecule Raman Scattering as a Probe of Surface Dynamics

Time-Dependent Single-Molecule Raman Scattering as a Probe of Surface Dynamics

Single molecule raman spectroscopy and local work function fluctuations

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