Synergistic Intra- and Intermolecular Noncovalent Interactions for Ultralong Organic Phosphorescence.

Metal-free ultralong organic phosphorescence (UOP) materials have attracted significant attention owing to their anomalous photophysical properties and potential applications in various fields. Here, three pyrimidine-based organic luminogens, 9-(pyrimidin-2-yl)-9H-carbazole, 9-(4,6-dimethylpyrimidin-2-yl)-9H-carbazole, and 9-(5-bromopyrimidin-2-yl)-9H-carbazole are designed and synthesized, which show efficient yellow UOP with the longest lifetimes up to 1.37 s and the highest absolute phosphorescence quantum yields up to 23.6% under ambient conditions. Theoretical calculations, crystal structures, and photophysical properties of these compounds reveal that intramolecular hydrogen bonding, intermolecular π-π interactions, and intermolecular electronic coupling are responsible for forming dimers and generating highly efficient UOP. Their efficacy as solid materials for data encryption is demonstrated.

Exploring the differential mechanisms of carotenoid biosynthesis in the yellow peel and red flesh of papaya.

BACKGROUND: Red-fleshed papaya is a good material to study the different carotenoids accumulation mechanism in the peel and flesh. Although the peel and flesh of papaya closely integrated into one body, the flesh coloration changing from white to red, while the exocarp coloration changing from green to yellow. In this study, the major carotenoids accumulation and the expression patterns of key carotenoid biosynthesis pathway genes in the process of papaya fruit ripening were studied, and the carotenoid biosynthetic pathways in the yellow peel and red flesh of papaya were investigated. RESULTS: The carotenoid composition in papaya flesh and peel were different. The major carotenoids were lutein and ß-carotene in the peel, while lycopene in the flesh. The accumulation of carotenoids, including lycopene, ß-carotene, and ß-cryptoxanthin were considered to cause the orange-red color of papaya cv. 'Daqing No.10' flesh. The color of peel changed from green to yellow because of the fast degradation of chlorophyll and the appearance of carotenoids such as lutein and ß-carotene. Thirteen genes that encode enzymes in the carotenoid biosynthetic pathway were detected in papaya fruit transcriptome: two phytoene synthase (PSY1, PSY2), two phytoene desaturase (PDS1, PDS2), one ζ-carotene desaturase (ZDS), four lycopene cyclase (CYCB, LCYB1, LCYB2, LCYE), one ß-carotene hydroxylase (CHYB), one carotene ε-monooxygenase (LUT1), one violaxanthin de-epoxidase (VDE), and one zeaxanthin epoxidase (ZEP). The results of RNA-Seq and RT-qPCR showed the expression of carotenoid biosynthetic pathway genes was consistent with the change of carotenoid content. Carotenoid biosynthetic pathways in the yellow peel and red flesh of papaya were analysed based on the major carotenoids accumulation and the expression patterns of key carotenoid biosynthesis pathway genes. There was only a ß-branch of carotenoid biosynthesis in the flesh of papaya, while there were both α- and ß-branch of carotenoid biosynthesis in papaya peel. In the process of papaya fruit ripening, the α-branch was inhibited and the ß-branch was enhanced in the peel. CONCLUSIONS: The differential carotenoid accumulation and biosynthesis pathway genes expression in peel and flesh, lay a foundation for further study and provide further insights to control fruit color and improve fruit quality and appearance.