Molecular Engineering for Modulating Photocatalytic Hydrogen Evolution of Fully Conjugated 3D Covalent Organic Frameworks

Covalent organic frameworks (COFs) have recently shown great potential for photocatalytic hydrogen production. Currently almost all reports are focused on two-dimensional (2D) COFs, while the 3D counterparts are rarely explored due to their non-conjugated frameworks derived from the sp3 carbon based tetrahedral building blocks. Here, we rationally designed and synthesized a series of fully conjugated 3D COFs by using the saddle-shaped cyclooctatetrathiophene derivative as the building block. Through molecular engineering strategies, we thoroughly discussed the influences of key factors including the donor-acceptor structure, hydrophilicity, specific surface areas, as well as the conjugated/non-conjugated structures on their photocatalytic hydrogen evolution properties. The as-synthesized fully conjugated 3D COFs could generate the hydrogen up to 40.36 mmol h-1 g-1. This is the first report on intrinsic metal-free 3D COFs in photocatalytic hydrogen evolution application. Our work provides insight on the structure design of 3D COFs for highly-efficient photocatalysis, and also reveals that the semiconducting fully conjugated 3D COFs could be a useful platform in clear energy-related fields.

Molecular Engineering of Cation Solvation Structure for Highly Selective Carbon Dioxide Electroreduction

Balancing the activation of H2 O is crucial for highly selective CO2 electroreduction (CO2 RR), as the protonation steps of CO2 RR require fast H2 O dissociation kinetics, while suppressing hydrogen evolution (HER) demands slow H2 O reduction. We herein proposed one molecular engineering strategy to regulate the H2 O activation using aprotic organic small molecules with high Gutmann donor number as a solvation shell regulator. These organic molecules occupy the first solvation shell of K+ and accumulate in the electrical double layer, decreasing the H2 O density at the interface and the relative content of proton suppliers (free and coordinated H2 O), suppressing the HER. The adsorbed H2 O was stabilized via the second sphere effect and its dissociation was promoted by weakening the O-H bond, which accelerates the subsequent *CO2 protonation kinetics and reduces the energy barrier. In the model electrolyte containing 5 M dimethyl sulfoxide (DMSO) as an additive (KCl-DMSO-5), the highest CO selectivity over Ag foil increased to 99.2 %, with FECO higher than 90.0 % within -0.75 to -1.15 V (vs. RHE). This molecular engineering strategy for cation solvation shell can be extended to other metal electrodes, such as Zn and Sn, and organic molecules like N,N-dimethylformamide.

Engineered Metallacycle-Based Supramolecular Photosensitizers for Effective Photodynamic Therapy

Although metallacycle-based supramolecular photosensitizers (PSs) have attracted increasing attention in biomedicine, their clinical translation is still hindered by their inherent dark toxicity. Herein, we report what to our knowledge is the first example of a molecular engineering approach to building blocks of metallacycles for constructing a series of supramolecular PSs (RuA-RuD), with the aim of simultaneously reducing dark toxicity and enhancing phototoxicity, and consequently obtaining high phototoxicity indexes (PI). Detailed in vitro investigations demonstrate that RuA-RuD display high cancer cellular uptake and remarkable antitumor activity even under hypoxic conditions. Notably, RuD exhibited no dark toxicity and displayed the highest PI value (≈406). Theoretical calculations verified that RuD has the largest steric hindrance and the lowest singlet-triplet energy gap (ΔE_ST , 0.61 eV). Further in vivo studies confirmed that RuD allows safe and effective phototherapy against A549 tumors.

Engineering Aptamers with Selectively Enhanced Biostability in the Tumor Microenvironment

Aptamers are emerging as promising molecular tools in cancer-targeted theranostics. Improving their in vivo stability has been a critical issue in promoting clinical translation, but such efforts could lead to more serious side effects resulting from prolonged retention in healthy organs. To address this problem, we developed an environment-responsive stabilization strategy for the selective enhancement of aptamer biostability in the tumor microenvironment (TME). Briefly, by means of the end extension of an ATP-responsive protection (ARP) module, the designed aptamer could be protected from nuclease degradation through the specific incorporation of ATP. Based on our in vivo results, this ARP-aptamer probe was effectively accumulated in tumors via aptamer-based molecular recognition. It showed selectively prolonged tumor retention time, but rapid digestion in healthy organs. Our strategy should provide a new paradigm for the development of organ-specific nucleic acid-based imaging and therapeutic agents.