Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

The synthesis, single crystal structures and chromic behaviour of three related Schiff bases (E)-2,4-di-tert-butyl-6-(((4-fluorophenyl)imino)methyl)phenol, (E)-2,4-di-tert-butyl-6-(((4-chlorophenyl)imino)methyl)phenol, and (E)-2,4-di-tert-butyl-6-(((4-bromophenyl)imino)methyl)phenol are reported. Two polymorphs of (E)-2,4-di-tert-butyl-6-(((4-fluorophenyl)imino)methyl)phenol were obtained which were found to have different photochromic properties. (E)-2,4-di-tert-butyl-6-(((4-chlorophenyl)imino)methyl)phenol, and (E)-2,4-di-tert-butyl-6-(((4-bromophenyl)imino)methyl)phenol were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tertiary butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than keto form based on the C-O(H) and imine C=N bond lengths and contained an intramolecular O-H···N hydrogen bond alongside weaker intermolecular C-H···O contacts.