Photofunctional Materials Based on Sheet Polymer Capped Organic Molecules for Visible‐Light‐Responsive Rewritable Paper

Historically, the recording of information over paper has always been regarded as the most important factor for maintaining records of human activities and spreading civilization. The present work is focusing to formulate hydride paper polymer sheets (HPPSs) using two fluorescence dyes (4-(2,6-diphenylpyridin-4-yl)-N,N-dimethylaniline) (F1) and (4-(2,6-bis(4-methoxyphenyl)pyridin-4-yl)-N,N-dimethylaniline) (F2) for the production of secure hybrid paper polymer sheets each with a different concentration. Mechanical properties, including tensile strength (MPa), Young`s modulus (MPa), elongation (mm), folding endurance, and tear resistance (mN m2/g), were determined. Furthermore, a topographical study was carried out using field emission scanning electron microscopes (FE-SEM). In comparison with native paper and polymer films, HPPSs demonstrated a significant improvement in mechanical properties. The fluorescence behavior of applied dyes was evaluated in both solution and solid states with UV–vis and photoluminescence (PL). The results confirmed that excitation of F1 and F2 dyes occurred at 393 nm and 448 nm and emission at 505 nm and 496 nm, respectively. Additionally, the third concentration (3% w/v) of both dyes was observed in solid state to achieve excellent resolution. In the first image, a note is shown under normal light, and in the second image, a picture is shown of the fluorescent security markings under UV light at 365 nm. Based on the results obtained, it is proven that the developed high stable as well as excellent mechanical security HPPSs can be used for paper-based information security due to their optical properties. Further, the density function theory (DFT) calculation was performed in order to identify the composition of the excited and ground states. According to the results, the N,N-dimethylamine substituent played a crucial role in explaining the extraordinarily high luminescence of F1 and F2.