A series of binary monolayers with different contents of C3(propyl) and C11(undecyl) alkyl chains were prepared by depositing a series of mixtures of C3 and C11 trichlorosilanes on planar silica surfaces. The terminal sites of C11 chains were selectively functionalized with a strong vibrational chromophore, (1,10-phenanthroline) tricarbonyl rhenium chloride (RePhen(CO)3Cl). Ultrafast structural dynamics of the functionalized binary monolayers on the time scale of picoseconds were investigated by heterodyne-detected 2D IR and heterodyne-detected transient grating (HDTG) experiments. Even with sample of which absorbance is less than 2 � 10-4 O.D., high quality 2D IR and HDTG spectra were obtained. The results show that the ultrafast structural fluctuations of binary monolayers are slower than pure C11 monolayers. The dynamics become increasingly slower as the C3 component rises and C11 chains are further separated from each other. The dynamics of C11 monolayers synthesized from dimethylmonochlorosilane is also shown to be much slower than the dynamics of C11 monolayers synthesized from trichlorosilanes. It is clear that the dynamics of functionalized monolayers depend heavily on the packing structure of alkyl chains, and the underlying mechanism is discussed.

Probing the ultrafast dynamics of pure and binary functionalized monolayers with heterodyne-detected 2D IR vibrational echo spectroscopy

248th National Meeting (2014)

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