Magic tetraphenylethene Schiff base derivatives with AIE, liquid crystalline and photochromic properties

Two novel aggregation-induced emission (AIE) active Schiff bases (P4C12 and P5C12) harnessing excited-state intramolecular proton transfer (ESIPT) process derived from tetraphenylethylene and 4-(dodecyloxy)-2-hydroxybenzaldehyde were reported. P4C12 exhibits photochromism in original powder and crystalline states. In contrast, P5C12 exhibits photochromism in original powder, but totally different photochromic and fluorescence properties in its two crystalline polymorphs. The reed leaf crystal (P5C12-A) exhibits very weak fluorescence and reversible photochromic behavior, while the small block crystal (P5C12–B) emits relatively stronger fluorescence without photochromism. Detailed investigations indicate that, different crystal packing styles result in different photoinactivation ways, accounting for different photochemical and photophysical properties. As photochromic molecules, P4C12 and P5C12 show reversible color and fluorescence changes upon UV light irradiation and visible light with good fatigue resistance, which makes them suitable for data storage and anti-counterfeiting materials. Moreover, P4C12 shows anisotropic crystal without liquid crystal texture, while P5C12 shows reversible liquid crystal with smectic phase.