Inkless Writing and Self-Erasing Security Feature of (Z)-1,2-Diarylacrylonitrile-Based Materials: A Confidential Data Communication.

Development of a novel organic luminescent material for inkless writing, and self-erasing application is a remarkable solution to reduce paper waste, recycling cost in the printing industry. These innovative materials also offer to reduce global warming due to the lower consumption of paper made from plants. To this endeavor, herein we report the design, synthesis and simple material fabrication of a donor-acceptor type (Z)-1,2-diarylacrylonitrile (1) compound, which in solid state displayed highly contrast and reversible vapochromism under the visible light as well as UV light. We found a unique multiphase luminescence switching from green (λmax = 535 nm) to yellow (λmax = 566 nm) and to orange-red (λ = 580, 640 nm) in solid state. This multiphase switching is induced through the gradual exclusion of entrapped DMSO molecules from the crystalline rod-like materials. Utilizing this purely organic material, we have demonstrated reversible inkless writing/printing on a cellulose strip by employing photothermal effect of sunlight in which sunlight acts as an "inkless pen". We were able to print complex designs utilizing this technique, which is invisible in ambient light and brighter in UV light. To our delight, the writing is self-erasable on keeping at sunlight for the prolonged period, upon keeping at ambient temperature, or instantly on warming. This remarkably smart function of our material offers cost-effective and environmentally benign technique for security data communication and confidential data printing.