Photochromic multicomponent crystalline materials based on N-salicylideneanilines

Promoter

Prof. Johan WOUTERS, UNamur, Laboratory of Structural Biological Chemistry (CBS)

Jury

Laurence LEHERTE (UNamur), présidente; Johan WOUTERS (UNamur), secrétaire; Claudio ROSCINI (Catalan Institute of Nanoscience and Nanotechnology); Tom LEYSSENS (UCLouvain); Benoît CHAMPAGNE (UNamur)

Summary

N-salicylideneaniline derivatives are among the most studied thermo- and photochromic systems. However, due to the volume requirements of the cis-trans photoisomerization at the basis of the photoswitching, photochromism is not easily encountered in the solid state; therefore, not every N-salicylideneaniline forms photochromic solids. Herein, cocrystallization is employed to induce photochromism in non-photochromic N-salicylideneaniline chromophores. The focus is put on the formation and characterization of isomorphous solids and their solid solutions with the aim to gain insights on the structural factors controlling the expression of photochromism in N-salicylideneanilines. N-salicylideneanilines and their cocrystals are obtained by mechanochemical synthesis performed in a ball mill. Structural features of the crystalline solids are analyzed by means of single-crystal and powder X-ray diffraction (PXRD), solid-state absorption and emission spectroscopy, FTIR spectroscopy, and 13C and 15N crosspolarization magic angle spinning (CPMAS) SSNMR spectroscopy. These results reveal how cocrystallization can be successfully employed with the aim to build a library of photochromic systems thanks to the fact that it changes both the free available volume of each molecule in the crystal and the intermolecular interactions.