Para-aryl-dithiols (PADT, HS-(C<sub>6</sub>H4)<sub>n</sub>-SH, n=1, 2 and 3) that contain two distal end –SH groups have been used extensively in molecular electronics, surface-enhanced Raman spectroscopy (SERS), and quantum electron tunneling between gold and silver nanoparticles (AuNPs and AgNPs). One common belief is that these dithiols cross-link noble metal nanoparticles as monolayer dithiolate spacers. Discussed in this presentation is our finding that PADTs are in predominantly monothiolate forms on AuNP or AgNP even in highly concentrated NaOH (6M) solutions. No PADT induced nanoparticle cross-linking were observed under any of the tested experimental conditions. Combined experimental and computational Raman investigation revealed a critical, but entirely overlooked pitfall in the existing Raman and SERS studies of PADT thiol deprotonation in solution and on NPs. The Raman activity of the S-H stretching feature is vanishingly small in PADT monothiolate, therefore, PADT monothiolate can be readily mistakenly identified as PADT dithiolate. Methods for improving the reliability of Raman and SERS spectral interpretation will be discussed.

On the possiblity of the para-aryl-dithiols cross-linking plasmonic nanoparticles as dithiolates

249th National Meeting (2015)

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