Meso-tetrakis(3,4,5-trimethoxyphenyl)porphyrin derivatives: Synthesis, spectroscopic characterizations and adsorption of NO₂

This work focuses on new materials based on the addition of zinc as specifically metal centers for the capture of NO₂ gas with DFT calculations. This study aims at the synthesis and the spectroscopic characterizations of the free base meso-tetrakis-,(3,4,5trimethoxyphenyl)porphyrin (H₂TTMP) (I), meso tetrakis(3,4,5trimethoxyphenyl)porphyrinato)zinc(II) complex [Zn(TTMP)] (II) and the (4-cyanopyridine) meso-tetrakis - (3,4,5-trimethoxyphenyl)porphyrinato)zinc(II) [Zn(TTMP)(4-CNpy)] (III). X-ray molecular structure of (III) displays that the crystal lattice of the five-coordinated zinc(II) coordination compound, is made up of two dimensional layers parallel to the [0 0 1] direction sustained by C–H⋯Cg and Cg⋯Cg π inter and intra-molecular interactions. Notably, the presence of voids of 1.2 Å and a grid of 0.7 Å are located between the 2D layers. DFT calculations on the three porphyrin derivatives were carried out and results indicated an agreement with both IR and UV-vis experimental data. The adsorption behaviors of the toxic NO₂ gas molecules on the porphyrin derivatives were investigated using first-principles density functional theory. Based on the MEP of (I)–(III) molecules and the MEP of NO₂ and the calculation of the adsorption energies, we suggest that compound (II) has the best attraction. More importantly, after NO₂ chemi-sorption on porphyrin derivatives, a remarkable red-shift is observed in the optical spectra, especially for II/NO₂ complex, thus offering a good index to detect the binding of NO₂. The optical spectra can therefore be used to detect the presence of NO₂ and porphyrin derivatives indicate appropriate properties to establish good NO₂ sensors.