DNA‐Grafted Supramolecular Polymers: Helical Ribbon Structures Formed by Self‐Assembly of Pyrene–DNA Chimeric Oligomers

The controlled arraying of DNA strands on adaptive polymeric platforms remains a challenge. Here, the noncovalent synthesis of DNA‐grafted supramolecular polymers from short chimeric oligomers is presented. The oligomers are composed of an oligopyrenotide strand attached to the 5′‐end of an oligodeoxynucleotide. The supramolecular polymerization of these oligomers in an aqueous medium leads to the formation of one‐dimensional (1D) helical ribbon structures. Atomic force and transmission electron microscopy show rod‐like polymers of several hundred nanometers in length. DNA‐grafted polymers of the type described herein will serve as models for the development of structurally and functionally diverse supramolecular platforms with applications in materials science and diagnostics.     

Supramolecular Hemicage Cobalt Mediators for Dye‐Sensitized Solar Cells

A new class of dye‐sensitized solar cells (DSSCs) using the hemicage cobalt‐based mediator [Co(ttb)]^2+/3+ with the highly preorganized hexadentate ligand 5,5′′,5′′′′‐((2,4,6‐triethyl benzene‐1,3,5‐triyl)tris(ethane‐2,1‐diyl))tri‐2,2′‐bipyridine (ttb) has been fully investigated. The performances of DSSCs sensitized with organic D –π–A dyes utilizing either [Co(ttb)]^2+/3+ or the conventional [Co(bpy)₃]^2+/3+ (bpy=2,2′‐bipyridine) redox mediator are comparable under 1000 W m^?2 AM 1.5 G illumination. However, the hemicage complexes exhibit exceptional stability under thermal and light stress. In particular, a 120‐hour continuous light illumination stability test for DSSCs using [Co(ttb)]^2+/3+ resulted in a 10 % increase in the performance, whereas a 40 % decrease in performance was found for [Co(bpy)₃]^2+/3+ electrolyte‐based DSSCs under the same conditions. These results demonstrate the great promise of [Co(ttb)]^2+/3+ complexes as redox mediators for efficient, cost‐effective, large‐scale DSSC devices.     

Enhancing Fullerene‐Based Solar Cell Lifetimes by Addition of a Fullerene Dumbbell

Cost‐effective, solution‐processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon‐based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long‐term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM‐based OPV device is reported. The addition of only 20 % of this novel fullerene not only leads to improved device efficiencies, but more importantly also to a dramatic increase in morphological stability under simulated operating conditions. Dynamic secondary ion mass spectrometry (DSIMS) and TEM are used, amongst other techniques, to elucidate the origins of the improved morphological stability.     

Redesigning the DNA‐Targeted Chromophore in Platinum–Acridine Anticancer Agents: A Structure–Activity Relationship Study

Platinum–acridine hybrid agents show low‐nanomolar potency in chemoresistant non‐small cell lung cancer (NSCLC), but high systemic toxicity in vivo. To reduce the promiscuous genotoxicity of these agents and improve their pharmacological properties, a modular build–click–screen approach was used to evaluate a small library of twenty hybrid agents containing truncated and extended chromophores of varying basicities. Selected derivatives were resynthesized and tested in five NSCLC cell lines representing large cell, squamous cell, and adenocarcinomas. 7‐Aminobenz[c]acridine was identified as a promising scaffold in a hybrid agent ( P1–B1 ) that maintained submicromolar activity in several of the DNA‐repair proficient and p53‐mutant cancer models, while showing improved tolerability in mice by 32‐fold compared to the parent platinum–acridine ( P1–A1 ). The distribution and DNA/RNA adduct levels produced by the acridine‐ and benz[c]acridine‐based analogues in NCI‐H460 cells (confocal microscopy, ICP‐MS), and their ability to bind G‐quadruplex forming DNA sequences (CD spectroscopy, HR‐ESMS) were studied. P1–B1 emerges as a less genotoxic, more tolerable, and potentially more target‐selective hybrid agent than P1–A1 .     

Water‐Dependent Optical Activity Inversion of Chiral DNA–Silica Assemblies

Chirality is widely found in nature and is expressed hierarchically in many organic–inorganic hybrid materials. Optical activity (OA) is the most fundamental attribute of these chiral materials. In this study, we found that the OA of impeller‐like chiral DNA–silica assemblies (CDSAs) was inverted with the addition of water. The state of DNA under dry and wet conditions, and the dual chirality of chiral DNA layers and twisted helical arrays of opposite handedness in CDSAs were considered to exert predominant effects on the OAs. The circular dichroism (CD) responses for the dry CDSAs were mostly attributed to the chiral arrangement of DNA layers, whereas the opposite CD responses for the wet CDSAs primarily originated from twisted helical arrays of DNA molecules. The observed CD signals were a super‐position of the two opposing OA responses. The increase in the longitudinal relation of DNA molecules due to the recovery of a double‐helical structure of DNA in the presence of water was considered to be the reason for the increase in intensity of the CD signals that originated from the twisted helical array, which led to the inversion of OA of the CDSAs. The inversion of the plasmon‐resonance‐based OAs for the chiral‐arranged achiral Ag nanoparticles (NPs) located in the channels of the CDSAs in dry and wet states further confirmed the dual chirality of DNA packing. Such research on DNA assemblies and metal NPs with dual, opposite chirality assists in the understanding of DNA hierarchical chirality in living systems and the creation of macroscopic ordered helical materials and biosensors.     

Internal Probing of the Supramolecular Organization of Pyrene‐Based Organogelators

A thorough study of the unexpected spectroscopic behavior of two new luminescent pyrene‐urea‐based organogelators is rationalized as a function of their aggregation state and provides a key method to probe the supramolecular organization of the material.     

DNA‐Based Oligochromophores as Light‐Harvesting Systems

The chromophores ethynyl pyrene as blue, ethynyl perylene as green and ethynyl Nile red as red emitter were conjugated to the 5‐position of 2′‐deoxyuridine via an acetylene bridge. Using phosphoramidite chemistry on solid phase labelled DNA duplexes were prepared that bear single chromophore modifications, and binary and ternary combinations of these chromophore modifications. The steady‐state and time‐resolved fluorescence spectra of all three chromophores were studied in these modified DNA duplexes. An energy‐transfer cascade occurs from ethynyl pyrene over ethynyl perylene to ethynyl Nile red and subsequently an electron‐transfer cascade in the opposite direction (from ethynyl Nile red to ethynyl perylene or ethynyl pyrene, but not from ethynyl perylene to ethynyl pyrene). The electron‐transfer processes finally provide charge separation. The efficiencies by these energy and electron‐transfer processes can be tuned by the distances between the chromophores and the sequences. Most importantly, excitation at any wavelength between 350 and 700 nm finally leads to charge separated states which make these DNA samples promising candidates for light‐harvesting systems.     

Prospects of Graphene as a Potential Carrier‐Transport Material in Third‐Generation Solar Cells

Third‐generation solar cells are understood to be the pathway to overcoming the issues and drawbacks of the existing solar cell technologies. Since the introduction of graphene in solar cells, it has been providing attractive properties for the next generation of solar cells. Currently, there are more theoretical predictions rather than practical recognitions in third‐generation solar cells. Some of the potential of graphene has been explored in organic photovoltaics (OPVs) and dye‐sensitized solar cells (DSSCs), but it has yet to be fully comprehended in the recent third‐generation inorganic–organic hybrid perovskite solar cells. In this review, the diverse role of graphene in third‐generation OPVs and DSSCs will be deliberated to provide an insight on the prospects and challenges of graphene in inorganic–organic hybrid perovskite solar cells.     

Hole‐Transport Materials for Perovskite Solar Cells

The pressure to move towards renewable energy has inspired researchers to look for ideas in photovoltaics that may lead to a major breakthrough. Recently the use of perovskites as a light harvester has lead to stunning progress. The power conversion efficiency of perovskite solar cells is now approaching parity (>22 %) with that of the established technology which took decades to reach this level of performance. The use of a hole transport material (HTM) remains indispensable in perovskite solar cells. Perovskites can conduct holes, but they are present at low levels, and for efficient charge extraction a HTM layer is a prerequisite. Herein we provide an overview of the diverse types of HTM available, from organic to inorganic, in the hope of encouraging further research and the optimization of these materials.