Invisible photochromism and optical anti-counterfeiting based on D-A type inverse diarylethene
In most cases, inverse type diarylethenes (DAEs) exhibit bathochromic shift of π-conjugation absorption band after photocyclization, which leads to “visible” closed forms and “visible” photochromic behaviors. The reason of bathochromic shift is that the lone pair electrons on sulfur atoms of thiophene rings function as π-electrons and participate in π-conjugation. To make photochromic behaviors “invisible”, we introduced electron-withdrawing aldehyde groups into the inverse DAE to endow lone pair electrons on sulfur atoms with more n-electron characteristics and achieved the hypsochromic shift of π-conjugation absorption band after photocyclization. As a result, the absorption changes of aldehydes modified DAE (IDAEo-2CHO) remained “invisible” during isomerization, and only fluorescence changes can be observed by naked eye after photocyclization. Taking advantage of this unique optical feature of IDAEo-2CHO, anti- counterfeiting applications were carried out.