Electron transfer-based photochromism from bidirectional selection of free radicals in multifunctional liquid crystal elastomers

New theories and methods are needed to guide the design and preparation of pure organic photoresponsive materials; however, the design of photochromic materials usually relies on the theory associated with traditional photoisomerization. In this work, the integration of 1,4-benzenedimethanamine, an aromatic diamine as a chain extender in the structure of liquid crystal elastomers (LCEs), has endowed the material with unique photochromic properties. Electron paramagnetic resonance and photoinitiator splitting analysis proved the free radicals-mediated electron transfer triggered photochromism. Further theoretical calculations indicate that the photochromic effect is the result of bidirectional selection between two types of free radicals. Specifically, 1,4-phenylenedimethanamine can lose electrons under ultraviolet (UV) light to produce cationic radicals, and an electron transfer process occurs when a radical (from the photoinitiator) with a matching energy level is present resulting in photochromic behavior, which is proven to be expanded to non-LCE systems with similar structural characteristic. The integration of dual photochromic/fluorescent functions of LCE realizes applications in the field of information recording and encryption based on the competition between photochromic and photoluminescent behaviors. Due to the temperature responsiveness of the LCE colored state, it also shows potential for application in the field of supervised cold chain transportation.