Gauging Molecular Orientation through Time Domain Simulations of Surface-Enhanced Raman Scattering

Abstract

Molecular reorientation dynamics modulate the physical and chemical properties of molecules at interfaces. This is particularly the case for organic molecules interacting with metallic surfacesstructural motifs of current interest to ultrasensitive chemical/biological detection/imaging. In this context, surface-enhanced Raman scattering (SERS) can be used to gauge the orientation of molecules in the immediate vicinity of plasmonic metals. Herein, we analyze SERS spectra of two aromatic thiols (4-mercaptobenzonitrile and thiophenol) chemisorbed onto silver substrates using ab initio molecular dynamics-based Raman spectral simulations that account for the optical response of molecules in the bulk and oriented molecules at the surface. Through a comparison with prior works aimed at gauging the orientation of our two model systems on metallic substrates, we describe the advantages and discuss the limitations of our described models and approach to gauging the orientation of molecules on metals through time domain simulations of their SERS signatures.

Tip-Enhanced Multipolar Raman Scattering

“…Aside from minor variations in the relative intensities, the spectra are identical and exhibit the familiar dipolar Raman lines of TBN. These Raman-allowed transitions appear at 1078, 1179, 1206, 1586, and 2225 cm –1 (green spectrum in Figure A), and they are assigned elsewhere. , Several weaker (formally Raman-forbidden) transitions are also observed in the spatially averaged spectra, appearing as a broadened feature in the 1225–1500 cm –1 region (shaded region, Figure A). Similar peaks were previously observed in SERS from TBN at plasmonic Au nanoparticle–Au surface junctions .…”

“…We isolate several single-pixel spectra in Figure A to illustrate the principle. Besides the familiar dipolar Raman spectrum of TBN, , two additional distinct spectra are immediately noticeable. This first is predominated by a ∼ 1326 cm –1 band.…”

“…This is consistent with our recent SERS report, whereby chemisorption of TBN onto roughened silver only slightly affects its spectral features. 39 Note that the simulated spectra represent the Euler average, which does not take into account vector components of the field(s). In this context, we have previously explored TBN through tensorial Raman scattering simulations, which account for nonequilibrium chemical effects, conformational flexibility, anharmonicity, (in)complete sampling of the full phase space of the molecule, as well as directional local optical fields.…”

Tip-Enhanced Raman Nanospectroscopy of Smooth Spherical Gold Nanoparticles

“…Second, the predicted resonance positions of the neutral TBN and Au3−TBN complex are in agreement with prior Raman and SERS studies. 27,30 Third, the calculated absolute resonance maximum of the anion (∼2135 cm −1 ) and frequency difference (∼100 cm −1 ) between the neutral and anionic forms are in close agreement with their experimental analogues. On the basis of these calculations and prior analyses, 27 the observed ∼2136 cm −1 peak can also be assigned the anionic form of TBN.…”

Нанокластеры Серебра В Биохимии И Медицине (Обзор)

“…Ñëîaeíûå ãèáðèäíûå ñòðóêòóðû, ñîñòîÿùèå èç íàíîðàçìåðíûõ íåîðãàíè÷åñêèõ êëàñòåðîâ è îðãàíè÷åñêèõ ëèãàíäîâ, ïðåäñòàâëÿþò ñîáîé èäåàëüíóþ ìîäåëü äëÿ ïîíèìàíèÿ äåéñòâèé ðàçëè÷íûõ ñèë, âçàèìîäåéñòâóþùèõ ìåaeäó ñîáîé â ïðîöåññàõ ñàìîîðãàíèçàöèè ñëîaeíûõ îð-ãàíè÷åñêèõ ìàêðîìîëåêóë; îáû÷íî ýòè êëàñòåðû ìîãóò ëèáî êîíêóðèðîâàòü, ëèáî ïðîÿâëÿòü íåêîòîðóþ òåíäåíöèþ ê êîîïåðàöèè ñ èíûìè âàðèàíòàìè âçàèìîäåéñòâèé ìåaeäó òàêèìè ìîëåêóëàìè, íàïðèìåð, âîäîðîäíûå ñâÿçè, ðàçíîîáðàçíûå ãèäðîôîáíûå âçàèìîäåéñòâèÿ, à òàêaeå ïðîöåññû îáðàçîâàíèÿ p-p-êîìïëåêñîâ è ñâÿçûâàíèå êàòèîíîâ p-ñâÿçÿìè ðàçíîîáðàçíûõ îðãà-íè÷åñêèõ ëèãàíäîâ, ÷òî çàòåì â áîëüøîé ñòåïåíè îïðåäåëÿþò ïîâåäåíèå ñàìèõ ãèáðèäíûõ ìîëåêóë [43].  êà÷åñòâå âîçìîaeíîãî ïðèìåðà ìîaeíî ïðèâåñòè âàðèàíò õèìè÷åñêîé ñîðáöèè 2 àðîìàòè÷åñêèõ òèîëîâ (4-ìåðêàïòîáåíçîíèòðèëà è òèîôåíîëà) íà ïîâåðõíîñòè ñåðåáðÿíîãî ñóáñòðàòà, êîòîðàÿ îïðåäåëÿëà îðèåíòàöèþ èõ ìîäåëüíûõ ñèñòåì [44]. Êðîìå òîãî, àíàëèç âèäèìîé îáëàñòè ñïåêòðîâ ìîëåêóë ï-ìåòèëòèîôåíîëà, 1-áóòàíòèîëà è äåöèëàìèíà ñ äâóõìåðíûìè íàíî-÷àñòèöàìè ñåðåáðà îäíîçíà÷íî óêàçûâàë íà òî, ÷òî ïðèñóòñòâèå ïîñëåäíèõ ïðèâîäèëî ê òðàíñôîðìàöèè íàñûùåííûõ öåïåé ìîëåêóë â íåíàñûùåííûå [45].…”