2,4,6-Trinitrotoluene (TNT) forms a red-colored Meisenheimer complex with 3-aminopropyltrienthoxysilane (APTES) both in solution and on solid phase. The TNT-APTES complex is unique since it forms yellow-colored complexes with 2,4,6-trinitrophenol and 4-nitrophenol, and no complex with 2,4-dinitrotoluene. The absorption spectrum of TNT-APTES has two absorption bands at 530 and 650nm, while APTES complexes with 2,4,6-trinitrophenol and 4-nitrophenol have absorption maxima at around 420nm, and no absorption change for 2,4-dinitrotoluene. The TNT-APTES complex facilitates the exchange of the TNT-CH<inf>3</inf> proton/deuteron with solvent molecules. The red color of TNT-APTES is immediately visible at 1μM of TNT.
Hughes, S., Dasary, S. S. R., Begum, S., Williams, N., & Yu, H. (2015). Meisenheimer complex between 2,4,6-trinitrotoluene and 3-aminopropyltriethoxysilane and its use for a paper-based sensor. Sensing and Bio-Sensing Research, 5, 37–41. https://doi.org/10.1016/j.sbsr.2015.06.003