Following the Azide‐Alkyne Cycloaddition at the Silica/Solvent Interface with Sum Frequency Generation

Abstract

The Cu(I) -catalyzed 1,3-dipolar azide-alkyne cycloaddition (CuAAC) has arisen as one of the most useful chemical transformations for introducing complexity onto surfaces and materials owing to its functional-group tolerance and high yield. However, methods for monitoring such reactions in situ at the widely used silica/solvent interface are hampered by challenges associated with probing such buried interfaces. Using the surface-specific technique broadband sum frequency generation (SFG), we monitored the reaction of a benzyl azide monolayer in real time at the silica/methanol interface. A strong peak at 2096 cm(-1) assigned to the azides was observed for the first time by SFG. Using a cyano-substituted alkyne, the decrease of the azide peak and the increase of the cyano peak (2234 cm(-1) ) were probed simultaneously. From the kinetic analysis, the reaction order with respect to copper was determined to be 2.1, suggesting that CuAAC on the surface follows a similar mechanism as in solution.

Influence of the grafting process on the orientation and the reactivity of azide-terminated monolayers onto silica surface

“…The second way to obtained pure azide-terminated SAMs consists in the direct grafting of the pre-synthesized azido silylated coupling agent. Generally, commercially available organosilanes such as 11-azidoundecyltrimethoxysilane and p-azidomethylphenyltrimethoxysilane [37] were used to prepare azide-terminated SAMs. Recently, we have reported a versatile synthetic methodology to prepare various azidosilylated coupling agents using the platinum-catalyzed hydrosilylation of stable olefinic precursors bearing an azide group [38].…”

“…This new possibility opens the way to obtain new azide-terminated monolayers with modular composition and structure, leading to original physicochemical properties. There are few examples of the preparation of azide-terminated SAMs onto silica surface by the direct grafting of azido-silylated compounds using the conventional deposition methods such as solution immersion [37,[39][40][41][42] and chemical vapor deposition [43,44]. Only one example describes the deposition of an azide-terminated monolayer by the Langmuir-Blodgett technique [45].…”

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

“…It is a challenge to measure orientation heterogeneity, even with the Gaussian distribution model. For decades, surface-specific vibrational sum frequency generation spectroscopy (referred to as 1D VSFG hereafter) [7][8][9][10][11][12][13][14][15] has been applied to determine the mean tilt angle, under the assumption of a narrow orientational distribution. However, by assuming a narrow angular distribution, the orientational distribution knowledge is lost, and the measured mean tilt angle can deviate from the real mean tilt angle when the orientational distribution is large, which is the well-known "magic angle" challenge.…”

The thermal reorganization of DNA immobilized at the silica/buffer interface: a vibrational sum frequency generation investigation

“…Moreover, we did not observe any appreciable signal for the benzyl azide monolayer in the presence of water (data not shown) and only very weak signal in the C-H region above 2850 cm À1 at the solid/air interface. 35 To aid in the assignment of the spectra, we reviewed the examples of IR absorbance and Raman spectroscopic measurements of the pure thymine nucleobase lacking the deoxyribose group in solution and the solid state. [36][37][38][39][40] Three to four peaks were generally observed between 2850 and 3000 cm À1 in both types of spectroscopy.…”