Adduct of magnesium tetraphenylporphyrin with aniline for colorimetric detection of SO2

Adduct of magnesium tetraphenylporphyrin (MgTPP) with aniline for colorimetric detection of SO2 was investigated in CH2Cl2 by steady-state fluorescence and UV-vis absorption spectroscopic techniques. The UV-vis spectra showed that the increasing aniline concentrations resulted in red shift of 3 nm for MgTPP Soret absorption band. Once introduced, SO2 competes with MgTPP for aniline, which eventually leads to the release of MgTPP and changes in the solution color/absorption. The fluorescence spectra suggested that MgTPP interacted with aniline to form 1:1 molecular adducts, and showed that the binding of MgTPP with aniline with the binding constants of 1.58-1.64 is not only endothermal but entropy-driven with ΔH = 1.622 kJ mol−1, ΔS = 9.389 J mol−1 K−1, and ΔG = −1.585 kJ mol−1 at T = 298.15 K.