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Multifaceted adsorption of α-cyano-4-hydroxycinnamic acid on silver colloidal and island surfaces
Jung, Dawoon,Jeon, Kooknam,Yeo, Juhyun,Hussain, Shafqat,Pang, Yoonsoo Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.425 No.-
<P><B>Abstract</B></P> <P>The surface adsorption of organic nitrile compounds on the silver colloidal and island surfaces has been studied using surface-enhanced Raman scattering (SERS). α-Cyano-4-hydroxycinnamic acid (CHCA) with nitrile and carboxyl groups shows various surface adsorption on the silver surfaces. In acidic conditions, the surface adsorption of CHCA via the nitrile group with a more or less tilted geometry to the surface was found. When the solution pH increases, the carboxylate and nitrile groups of deprotonated CHCA participate in the surface adsorption, whereas the molecular plane of CHCA becomes more parallel to the surface. The ν(CN) band in SERS of CHCA is the indicator of the surface adsorption geometry. The strongly red-shifted and broadened ν(CN) band in SERS represents the surface adsorption via π-electrons of the CN bond (side-on geometry; π-coordination). Nitriles adsorbed on the surface via the nonbonding electron pair of the nitrogen atom (end-on geometry; σ-coordination) often cause the blue-shifts and small band broadening in ν(CN) in SERS. The surface adsorption geometry of organic nitriles based on many previous experimental results was further confirmed by the surface adsorption of CHCA on the silver island surfaces and dinitrile compounds on the silver colloidal surfaces.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Organic nitriles show two distinct adsorption geometries on silver nanosurfaces. </LI> <LI> Surface adsorption via nitrile and carboxylate groups showed strong pH dependence. </LI> <LI> SERS is a powerful tool for the molecular structure of surface-adsorbed species. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jen, Myungsam,Lee, Sebok,Jeon, Kooknam,Hussain, Shafqat,Pang, Yoonsoo American Chemical Society 2017 The Journal of physical chemistry B Vol.121 No.16
<P>We report time-resolved stimulated Raman spectra of alizarin in DMSO solution with, 403 nm excitation. Upon photo excitation, the intramolecular proton transfer reaction of alizarin occurs in 70-80 fs, which is, confirmed by both the population growth and the frequency and bandwidth changes of skeletal vibrational modes of alizarin. Interestingly, the vibrational frequencies of v(C= C) and v(C=O) show opposite shifts during the reaction, which may implicate changes, in the resonance structure, of anthraquinone and the attached-carbonyl group. Vibrational relaxation in the potential surface of the proton transferred tautomer of alizarin and the population decay occurring-with two distinct time scales were also observed in addition to the solvation dynamics of DMSO solvent molecules.</P>