Giant absorption of light by molecular vibrations on a chip.

A Karabchevsky,A V Kavokin

doi:10.1038/srep21201

Abstract

Vibrational overtone spectroscopy of molecules is a powerful tool for drawing information on molecular structure and dynamics. It relies on absorption of near infrared radiation (NIR) by molecular vibrations. Here we show the experimental evidence of giant enhancement of the absorption of light in solutions of organic molecules due to the switch from ballistic to diffusive propagation of light through a channel silicate glass waveguide. We also experimentally address a dynamics of absorption as a function of time of adsorption of the organic molecules on a waveguide. The observed enhancement in diffusion regime is by a factor of 300 in N-Methylaniline and by factor of 80 in Aniline compared to the expected values in the case of ballistic propagation of light in a waveguide. Our results underscore the importance of a guide surface modification and the disordered molecular nano-layer in enhancement of absorption by amines on engineered integrated system.

Highlights

Vibrational overtone spectroscopy of molecules is a powerful tool for drawing information on molecular structure and dynamics
We show the experimental evidence of giant enhancement of the absorption of light in solutions of organic molecules due to the switch from ballistic to diffusive propagation of light through a channel silicate glass waveguide
The observed enhancement in diffusion regime is by a factor of 300 in N-Methylaniline and by factor of 80 in Aniline compared to the expected values in the case of ballistic propagation of light in a waveguide

Summary

OPEN Giant absorption of light by molecular vibrations on a chip

NIR data recorded on a waveguide from the droplet of 67% NMA diluted in Hex shows that in 35 minutes the centre of the N-H peak shifts from 14.75 μ m to 14.9 μ m, indicating that the concentration of NMA within the penetration depth of the evanescent NIR field increases with time This signal remains steady, demonstrating that a compact organic layer has formed near the surface and the Hex has been pushed beyond the evanescent field region (Fig. 2d). Despite the fact that the N-H overtone absorption band of Aniline in the NIR spectrum has stronger absorption compared to NMA, it exhibits a less pronounced transmittance resonance on a guide This observation can be explained by the increased hydrogen bonding existing between the amine molecules in aniline, which makes it less energetically preferential for them to reorganise and align with the surface (Fig. 4d)[14]. The affinity of aromatic amines to the surface of an integrated optical device makes our approach suitable for NIR detection and spectroscopy studies of amine based group materials such as anilines important for pharmaceutical and other chemical industries[21]

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Additional Information