Graphene quantum dots (GQDs) are a subset of fluorescent nanomaterials that have gained recent interest due to their photoluminescence properties and low toxicity and biocompatibility features for bioanalysis and bioimaging. However, it is still a challenge to prepare highly near-infrared (NIR) fluorescent GQDs using a facile pathway. In this study, NIR GQDs were synthesized from the biomass-derived organic molecule ciscyclobutane-1,2-dicarboxylic acid via one-step pyrolysis. The resulting GQDs were then characterized by various analytical methods such as UV−Vis absorption spectroscopy, fluorescence spectroscopy, dynamic light scattering, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Moreover, the photostability and stability over a wide pH range were also investigated, which indicated the excellent stability of the prepared GQDs. Most importantly, two peaks were found in the fluorescence emission spectra of the GQDs, one of which was located in the NIR region of about 860 nm. Finally, the GQDs were applied for cell imaging with human breast cancer cell line, MCF-7, and cytotoxicity analysis with mouse macrophage cell line, RAW 246.7. The results showed that the GQDs entered the cells through endocytosis on the fluorescence images and were not toxic to the cells up to a concentration of 200 μg/mL. Thus, the developed GQDs could be a potential effective fluorescent bioimaging agent. Finally, the GQDs depicted fluorescence quenching when treated with mercury metal ions, indicating that the GQDs could be used for mercury detection in biological samples as well.

A previously overlooked building block, cyclobutane-1,3-diacid (CBDA), is introduced to materials synthesis due to its great potentials. As an example of CBDA, α-truxillic acid or 2,4-diphenylcyclobutane-1,3-dicarboxylic acid, was readily synthesized from commercially available trans-cinnamic acid. This CBDA showed outstanding stability both in sunlight and upon heating. While its two carboxylic acid groups can be readily utilized in connecting with other molecules to form new materials, the cyclobutane ring was able to tolerate acid and base treatments showing good chemical stability. A series of cyclobutane-containing polymers (CBPs), namely poly-α-truxillates, were obtained by condensation between α-truxillic acid and diols including ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-petanediol, and 1,6-hexanediol. The structures of these poly-α-truxillates were analyzed by NMR, FT-IR, and HRMS. Powder X-ray diffraction results of the poly-α-truxillates indicated that they are semi-crystalline materials. Preliminary thermal, chemical, and photochemical tests showed that the poly-α-truxillates exhibited comparable stabilities to PET.

A novel renewable building block with a semirigid structure, (1α,2α,3β,4β)-2,4-di­(furan-2-yl)­cyclobutane-1,3-dicarboxylic acid (CBDA-5), was synthesized from furfural. The synthesis started with a Knoevenagel condensation between furfural and malonic acid, and a subsequent decarboxylation in the same pot, which produced 2-furanacrylic acid. The corresponding ester, ethyl-2-furanacrylate, was prepared by the Fisher or Steglich esterification of 2-furanacrylic acid with ethanol. Solvent-free [2 + 2] photodimerization of crystalline ethyl 2-furanacrylate was then carried out at −20 °C under blacklight to give diethyl 2,4-di­(furan-2-yl)­cyclobutane-1,3-dicarboxylate (CBDE-5). Afterward, CBDE-5 was hydrolyzed to give the corresponding dicarboxylic acid, CBDA-5. Both CBDE-5 and CBDA-5 were confirmed by NMR spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, high-resolution mass spectrometry (HRMS), and single-crystal X-ray diffraction (XRD). A preliminary study showed that CBDE-5 and CBDA-5 could be used as renewable building blocks to produce fully biobased polyesters. In this study, several “green” techniques were applied to prepare renewable building blocks, including solvent-free crystallization, solvent- and metal-free photodimerization, and the use of residential blacklight as an energy-efficient, cost-effective, and operator-friendly UV (ECO-UV) irradiation source in the stereoregular photocycloaddition.

The ability of diol monomers, such as 1,4-cyclohexanedimethanol (CHDM) and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), to replace the potentially hazardous BPA in the production of polyesters and polycarbonates with excellent thermal, optical, and...