Photochromism emergence in N-salicylidene P-aminobenzenesulfonate diallylammonium salts

N-Salicylidene p-aminobenzenesulfonate salts were prepared by in situ condensation of p-aminobenzenesulfonate diallylammonium salt and salicylaldehyde. Modulation of thermo- and photochromism was achieved by varying the alkyl chain length of the diallylammonium counter-cation. A structural-optical properties investigation reveals that both crystal packing and dihedral angle between aromatic rings of the N-salicylidene aniline switch are not sufficient to predict the occurrence of photochromism in the solid state. The available free space around the N-salicylidene p-aminobenzenesulfonate, in addition to the flexibility of the nearby environment, is shown to be of major importance for the cis→trans isomerisation to occur as well as for the stabilisation of the trans-keto form. Emergence of photochromic properties was determined from the diallylhexylammonium cation within the series of investigated counter-cations. High stability is observed for the trans-keto form of one polymorph of N-salicylidene p-aminobenzenesulfonate diallylhexylammonium salt (k=2.4×10-7s-1). Color scheme: Modulation of thermo/photochromism was achieved in a series of anil anionic switches (see figure). The available free space and the flexibility of the nearby environment around the anil account for the photochromic properties. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim