Photophysical Properties and Excited State Dynamics of Porous Organic Materials

Charge transfer complexes are charge separated states that are formed at donor - acceptor interfaces and play significant role in charge photogeneration. One of the main criteria for efficient charge transfer is suppression of charge recombination process. Previous experiments show that one of the most effective ways to inhibit recombination is an introduction of bridge molecules between donor and acceptor or increase the number of electron donating and withdrawing groups. These solutions are inspired by photosynthetic reaction centers where charge transfer occurs over long distances. Covalent Organic Frameworks (COFs) are advanced porous crystalline materials that can be constructed of multiple donor and acceptor building blocks. This approach improves efficiency of charge transfer by suppressing dissociation of polaron pairs. In the present work, photophysical and charge dynamics processes of various donor-acceptor systems, namely star-shaped carbazole-π-triazine organic chromophores, BTPA-cased donor-acceptor COFs, and metallophthalocyanine COFs, were investigated using the combination of steady-state spectroscopic techniques and time-resolved femtosecond transient absorption (TA) spectroscopy. The study on star-shaped carbazole-π-triazine organic chromophores showed that formation of charge transfer can be facilitated by positioning a bridging phenyl ring by creation of conjugated system. Nevertheless, the introduction of two phenyl bridge units can distort the coupling leading to weak charge migration from carbazole. Combination of BTPA (5,5\u27,5\u27\u27-(1,3,5-Benzenetriyl)tris[2-pyridinecarboxaldehyde]) and a series of three different organic precursors: 1,3,5-Tris(4-aminophenyl)benzene (TPB), 4,4\u27,4\u27\u27-Triaminotriphenylamine (TPA), and 1,3,5-Tris(4-aminophenyl)triazine (TPT) for the synthesis of COF showed that efficient charge transfer and slower recombination process can be achieved by incorporating stronger electron donating group, such as TPA, to enhance excited state dipole moment. Finally, the investigation of charge dynamics in COFs constructed using copper and nickel metallophthalocyanine linked to electron withdrawing 2,3,5,6-tetrafluoroterephthalonitrile (TFTPN) revealed the delocalization of charge between neighboring donor-acceptor units formed within 1.464 – 1.750 ps, which is further transferred between COF layers and dissociates between 0.662 – 3.383 ns

Dysregulation of YAP by ARF Stimulated with Tea-derived Carbon Nanodots

Abstract YAP is a downstream nuclear transcription factor of Hippo pathway which plays an essential role in development, cell growth, organ size and homeostasis. It was previously identified that elevation of YAP in genomics of genetic engineered mouse (GEM) model of prostate cancer is associated with Pten/Trp53 inactivation and ARF elevation hypothesizing the essential crosstalk of AKT/mTOR/YAP with ARF in prostate cancer. However, the detailed function and trafficking of YAP in cancer cells remains unclear. Using GEM microarray model, we found ARF dysregulates Hippo and Wnt pathways. In particular, ARF knockdown reduced non-nuclear localization of YAP which led to an increase in F-actin. Mechanistically, ARF knockdown suppressed protein turnover of β-catenin/YAP, and therefore enhanced the activity of AKT and phosphorylation of YAP. Moreover, we found tea-derived carbon dots can interact with ARF in nucleus that may further lead to the non-nuclear localization of YAP. Thus, we reported a novel crosstalk of ARF/β-catenin dysregulated YAP in Hippo pathway and a new approach to stimulate ARF-mediated signaling to inhibit nuclear YAP using nanomaterials implicating an innovative avenue for treatment of cancer