A new tetraphenylethene-based Schiff base: two crystalline polymorphs exhibiting totally different photochromic and fluorescence properties

Two different polymorphs of a new tetraphenylethene-based Schiff base 4-methoxy-2-(((4-(1,2,2-triphenylvinyl)phenyl)imino)methyl)phenol (TPENOMe) were obtained, which exhibit totally different photochromic and fluorescence properties. The square block-like crystal (TPENOMe-a) exhibits very weak fluorescence and reversible photochromic behavior, while the needle-like crystal (TPENOMe-b) emits relatively stronger orange fluorescence without photochromism. Detailed investigations of the crystal structures, fluorescence spectra and femtosecond transient absorption spectra of the two different polymorphs demonstrate that the different photoinactivation ways resulting from significantly different crystal packing styles may be responsible for the unprecedented various properties. Moreover, TPENOMe-a can be applied as visible light responsive rewritable paper with inkless writing and self-erasing properties. For the rewritable paper, 450 nm blue light can serve as the pen, while 460 to 570 nm light and white light are employed as the eraser. TPENOMe-b combined with TPENOMe-a can be used as a reusable data encryption material with both static and dynamic encryption-decryption processes.