Near-infrared raman spectra of azo dye produced by a nitrogen-dioxide-gas-selective coloration reaction in a porous glass chip

We directly observed azo dye in a porous glass chip by near-infrared (NIR) Raman spectroscopy. We produced the dye by a modified Saltzman reaction by using sulfanilamide (SFA) and N, N-dimethyl-1-naphthylamine (DMNA) as reage nts and used it for the selective sensing of atmospheric nitrogen dioxide g as (NO2). The use of NIR laser excitation is particularly advantageous for the direct measurement of azo dye because it avoids the problem of interfer ence from fluorescence. We obtained the 1597 cm(-1) band assigned to the ph enyl group stretching mode and the 1415 cm(-1) band assigned to the azo gro up stretching mode. The Raman intensity and visible absorption intensity of the peaks of the azo dye in a porous glass chip increased as we increased the exposure time to NO2. This allowed us to monitor the NO2-sensing reacti on in a porous glass chip using NIR Raman spectroscopy. Furthermore, we det ermined the depth profiles of the azo dye concentration in the porous glass chip by confocal NIR Raman spectroscopy and found that they were different in the early and later NO2-exposure stages. This result indicates that the consumption of the NO.-sensing reagents that accompany azo dye production occurs preferentially at the surface to the deeper regions of the porous gl ass chip.