[2 + 2] Photodimerization of Sulfonate Derivative of <i>trans</i>-Cinnamic Acid: Kinetics Study Using Solid State <sup>13</sup>C NMR and Hybrid Material Inclusion
Varun Kumar, Luca Fusaro, Carmela Aprile, Koen Robeyns, Yann Garcia
Abstract
A sulfonic acid, namely p-sulfocinnamic acid (psca), has been synthesized and characterized spectroscopically as well as by single crystal X-ray diffraction. The crystal structure of psca reveals that it fulfils Schmidt’s topochemical rules for [2 + 2] photodimerization and the molecules to be dimerized are arranged in head-to-tail manner, confirming psca to be an α-type polymorph. The [2 + 2] photodimerization of psca has been monitored using solid state 13C CP-MAS NMR spectroscopy which certifies a 100% photoconversion to yield to 4,4′-disulfonate-truxillic acid (dsta). The Avrami constant, n = 1.8(1), derived from the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, indicates that [2 + 2] photodimerization proceeds with a decreasing nucleation rate and formation of dsta occurs through a one-dimensional heterogeneous linear growth. The crystal structure of dsta unveils it to be a centrosymmetric molecule. The solvent molecules present in the crystal lattice interconnect all truxillic acid molecules through a 3D hydrogen bonding network. Guest insertion of psca into a selected inorganic host-network, as a proof of concept for hybrid materials design, provided [Fe(H2O)6](psca)2·2H2O, which has been structurally characterized and investigated by 57Fe Mössbauer spectroscopy.