A spectroscopic study of hexadecylquinolinium tricyanoquinodimethanide as a monolayer and in bulk

We have prepared Langmuir−Blodgett monolayers of hexadecylquinolinium tricyanoquinodimethanide (C16H33Q+-3CNQ-) on gold surfaces and characterized the structure by surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), reflection−absorption infrared spectroscopy (RAIRS), Raman spectroscopy, and water contact angle measurements. We compare the IR and UV−vis spectra of C16H33Q+-3CNQ- to a series of compounds that contain the key functional groups in the titled compound to help assign the spectral features. The surface spectroscopic measurements indicate that the molecules in the monolayer are aligned such that the two terminal cyano groups are adsorbed on the Au surface, and that the aliphatic chain is away from that surface. The thickness of the monolayer was measured by XPS to be ∼ 26 Å and suggests that the molecules are tilted ∼40° away from the surface normal. High-resolution XPS and spectroelectrochemical measurements of C16H33Q+-3CNQ- strongly suggest that it is a ground-state zwitterion in both the adsorbed and solvated forms.