Surface-Enhanced Raman Spectroscopy to Probe Reversibly Photoswitchable Azobenzene in Controlled Nanoscale Environments

Abstract

We apply in situ surface-enhanced Raman spectroscopy (SERS) to probe the reversible photoswitching of azobenzene-functionalized molecules inserted in self-assembled monolayers that serve as controlled nanoscale environments. Nanohole arrays are fabricated in Au thin films to enable SERS measurements associated with excitation of surface plasmons. A series of SERS spectra are recorded for azobenzene upon cycling exposure to UV (365 nm) and blue (450 nm) light. Experimental spectra match theoretical calculations. On the basis of both the simulations and the experimental data analysis, SERS provides quantitative information on the reversible photoswitching of azobenzene in controlled nanoscale environments.

Effect of Tether Conductivity on the Efficiency of Photoisomerization of Azobenzene-Functionalized Molecules on Au{111}

“…Raman signals for different mole fractions of the molecules were also calculated to gain a better understanding of the switching efficiencies of molecules on the substrate. The analogous calculations for Azo1 (without the Au cluster) have been previously reported 37 and are used here in elucidating the role of the tether. Figure 2 shows the overlay of simulated Raman spectra of Azo2 molecules attached to Au 3 clusters as a convolution of various mole fractions of trans and cis isomers.…”

“…The time constant from our study with Azo1 was found to be τ = 38 ± 13 min (unpublished results). 37 The reverse isomerization of Azo2 from cis to trans was also investigated by irradiating the sample with blue light (∼450 nm and power of 6 mW/cm 2 ), whereas Azo1 showed ∼90% reversibility in isomerization within 100 min of visible light illumination, 37 Azo2 did not exhibit complete reversibility, at least after 24 h of visible light illumination. Figure 6 shows a series of SERS spectra of the surface assembled with Azo2 under constant visible-light irradiation.…”

“…The time constant derived from the experimental curve was found to be 286 ± 37 min ( Figure 6) as opposed to the faster cis-to-trans photoisomerization of Azo1, which had a time constant of 75 ± 27 min (unpublished results). 37 Because of the increased conductivity in Azo2, the lifetime of the photoexcited state is lower than that in the case of nonconductive tether, resulting in decreased numbers of molecules that undergo photoisomerization over a period of time, resulting in significant difference in the time constants. The experimental studies for both of the molecules were performed under identical conditions, that is, sample preparation, concentration of switch molecules, the nanohole array periodicity of the substrate, power of UV and visible-light sources, and power and beam diameter of the Raman laser source.…”

“…22,38−40 Recently, surface-enhanced Raman spectroscopy (SERS) has been shown to be an excellent tool for following photoisomerization of functional molecules on the ensemble scale. 14,37,41 Although, the effects of the surrounding environment, 42,43 the coupling of the functional moiety to the substrate using a …”

A 1064 nm Dispersive Raman Spectral Imaging System for Food Safety and Quality Evaluation

“…However, a different chemical composition results in different vibrational modes specific to their chemical structure. The sharp peaks of metanil yellow at 1147 cm −1 and 1433 cm −1 , due to the N = N site are most definitive to its identification and quantification [67][68][69]. The 1631 cm −1 peak in turmeric spectrum is due to the carbonyl group.…”