Supramolecular Phthalimide Networks Via Tandem Diels-Alder Reaction-Aromatization Using Biomass-Derived Furanic Dienes.

The design and synthesis of phthalimide derivatives are important goals for applications in fields such as pharmaceutical science and optoelectronics. In the present study, a facile and convenient synthetic pathway (no heat or acid/catalyst needed) is devised to produce phthalimides from a biomass-derived furan by directly introducing an N-carbamate group at the C-2 position of the furan ring via thermal Curtius rearrangement. The electron-donating N-carbamate group increases the energy level of the highest occupied molecular orbital of the furan diene, resulting in a significant increase of the rate of the Diels-Alder reaction with maleimide compared to the conventional furfuryl furan. Interestingly, the Diels-Alder adduct smoothly undergoes aromatization (dehydration) to generate the phthalimide motif. It is shown that the biomass-derived phthalimides can produce supramolecular gels and act as sensors of basic anions like F- and CN- . The novel synthetic pathway to phthalimide derivatives from a biomass-derived furan can potentially be used to develop novel phthalimide motifs for a variety of applications.

Invisible ink mark detection in the visible spectrum using absorption difference.

One of popular techniques in gambling fraud involves the use of invisible ink marks printed on the back surface of playing cards. Such covert patterns are transparent in the visible spectrum and therefore invisible to unaided human eyes. Invisible patterns can be made visible with ultraviolet (UV) illumination or a CCD camera installed with an infrared (IR) filter depending on the type of ink materials used. Cheating gamers often wear contact lenses or eyeglasses made of IR or UV filters to recognize the secret marks on the playing cards. This paper presents an image processing technique to reveal invisible ink patterns in the visible spectrum without the aid of special equipment such as UV lighting or IR filters. A printed invisible ink pattern leaves a thin coating on the surface with different refractive index for different wavelengths of light, which results in color dispersion or absorption difference. The proposed method finds the differences of color components caused by absorption difference to detect invisible ink patterns on the surface. Experiment results show that the proposed scheme is effective for both UV-active and IR-active invisible ink materials.

Sequence discrimination of heterogeneous crossing of seal impression and ink-printed text using adhesive tapes.

This paper presents a technique to discriminate the sequence of stamped seal impression and ink-printed text in a document to detect falsely signed documents. In many Asian countries where a seal is widely used to endorse documents, a possibly forged document involves a seal impressed before the text is printed. The proposed method uses adhesive tapes with peel adhesion strength of approximately 25 oz/in. to exfoliate the top layer of the overlapping region of seal impression and ink-printed text in the document. A pair of digital images of the overlapping region, captured using an infinite focus microscope, is compared for color changes before and after the exfoliation with adhesive tapes. The proposed sequence discrimination index (SDI) measures the amount of color changes before and after the exfoliation to determine the sequence of seal impression and printed text. Experiment results show that the SDI successfully discriminates the sequence of seal impression and printed text for different types of ink cartridges and seal inkpads under various storage conditions, enabling forensic investigation of falsely signed documents with a seal.