We report on the study of the thermally induced nonlinear optical (NLO) properties of the commonly used organic solvents at the near-infrared range using spatial cross-phase modulation (SXPM). The results indicate that those solvents (alcohols, formic acid, and acetic acid) with −OH and −COOH functional groups have obvious NLO effect in the near-infrared range due to the third overtone absorption of the O−H band. In addition, the NLO effect of the ketones and aldehydes is enhanced when water or nitric acid is added, because the products with −OH and −COOH are generated, respectively, according to the nucleophilic addition reactions. Finally, real-time visualization of the acetone nucleophilic addition reaction is realized by monitoring the SXPM diffraction patterns' variation with time. This work not only is of importance in studying the NLO properties of the materials, e.g, interpreting the results performed in solutions and selecting suitable solvents, but also provides a simple way to visualize chemical reactions.

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