Tetraphenylborate Anion Induces Photochromism in N-Salicylideneamino-1-alkylpyridinium Derivatives Through Formation of Tetra-Aryl Boxes

N-Salicylideneanilines are interesting model compounds for understanding solid-state photochromism. The introduction of bulky substituents (trityl or tert-butyl groups) by chemical modification of the N-salicylideneaniline derivative is an effective method to build up photochromic solids. Alternatively, we propose, herein, a supramolecular approach to design photochromic materials which involves the introduction of a bulky anion in the structure. In this context, this is the first report on N-salicylideneamino-1-alkylpyridinium salts (iodide and tetraphenylboride salts). Iodide salts were obtained by alkylation of the parent N-salicylideneaminopyridine with the appropriate iodoalkane (iodomethane or iodoethane) in acetone. The iodide salts were used as the starting material for the production of tetraphenylborate salts by anion-exchange in methanol. All solids were characterized by means of X-ray diffraction and absorption spectroscopy. The effect of different counterions as well as the effect of the crystal structure on the solid-state photochromism is investigated.