Photoactive Systems Research Articles

Breaking photoswitch activation depth limit using ionising radiation stimuli adapted to clinical application

Electromagnetic radiation-triggered therapeutic effect has attracted a great interest over the last 50 years. However, translation to clinical applications of photoactive molecular systems developed to date is dramatically limited, mainly because their activation requires excitation by low-energy photons from the ultraviolet to near infra-red range, preventing any activation deeper than few millimetres under the skin. Herein we conceive a strategy for photosensitive-system activation potentially adapted to biological tissues without any restriction in depth. High-energy stimuli, such as those employed for radiotherapy, are used to carry energy while molecular activation is provided by local energy conversion. This concept is applied to azobenzene, one of the most established photoswitches, to build a radioswitch. The radiation-responsive molecular system developed is used to trigger cytotoxic effect on cancer cells upon gamma-ray irradiation. This breakthrough activation concept is expected to expand the scope of applications of photosensitive systems and paves the way towards the development of original therapeutic approaches.

Fundamental Study of the Optical and Vibrational Properties of Fx-AZB@MOF systems as Functions of Dye Substitution and the Loading Amount.

Controlling the switching efficiency of photoactive hybrid systems is an obligatory key prerequisite for systematically improving the design of functional materials. By modulating the degree of fluorination and the amount being embedded into porous hosts, the E/Z ratios of fluorinated azobenzenes were adjusted as both functions of substitution and the degree of loading. Octafluoroazobenzene (F8-AZB) and perfluoroazobenzene (F10-AZB) were inserted into porous DMOF-1. Especially for perfluoroazobenzene (F10-AZB), an immense stabilization of the E isomer was observed. In complementary molecular dynamics simulations performed at the DFTB (density functional tight binding) level, an in-depth characterization of the interactions of the different photoisomers and the host structure was carried out. On the basis of the resulting structural and energetic data, the experimentally observed increase in the amount of the Z conformer for F8-AZB can be explained, while the stabilization of E-F10-AZB can be directly related to a fundamentally different interaction motif compared to its tetra- and octafluorinated counterparts.

Multivariate Strategy Preparation of Nanoscale Ru-Doped Metal-Organic Frameworks with Boosted Photoactivity for Bioimaging and Reactive Oxygen Species Generation.

How to incorporate chromophores into MOFs is a key for the development of multifunctional photoactive systems. The poor internalization by cancer cells and low efficiency of ROS generation hamper the potential clinic application of Ru-based molecular agents. In this work, a nanoscale Ru-doped metal-organic framework Hf-UiO-Ru (Hf-Ru) with framework-boosted photoactivities was prepared via a multivariate strategy for use in bioimaging and ROS generation. The as-synthesized Hf-Ru nanocrystals not only maintain the well regular morphology and crystal structure in comparison with that of the Hf-UiO-66 prototype but also give an oxygen-independent emission with a much longer lifetime, higher quantum yield, and stronger ROS generation than molecular Ru(dcbpy)3. Additionally, the enhanced cellular uptake and high brightness in fluorescence and CT imaging of Hf-Ru nanocrystals have also been well studied in vitro. This multivariate strategy may be utilized as a general paradigm to develop a photoactive nanosystem for bioimaging and cancer treatment.

Photoactive Zr-aromatic hybrid thin films made by molecular layer deposition.

The principle of antimicrobial photodynamic therapy (PDT) is appealing because it can be controlled by an external light source and possibly the use of durable materials. However, to utilise such surfaces requires a process for their production that allows for coating on even complex geometries. We have therefore explored the ability of the emerging molecular layer deposition (MLD) technique to produce and tune PDT active materials. This study demonstrates how the type of aromatic ligand influences the optical and antimicrobial properties of photoactive Zr-organic hybrid thin films made by MLD. The three aromatic dicarboxylic acids: 2,5-dihydroxy-1,4-benzenedicarboxylic acid, 2-amino-1,4-benzenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid have been combined with ZrCl4 to produce hybrid coatings. The first system has not been previously described by MLD and is therefore more thoroughly investigated using in situ quartz crystal microbalance (QCM), Fourier transform infrared (FTIR) and UV-Vis spectroscopy. The antibacterial phototoxic effects of Zr-organic hybrids have been explored in the Staphylococcus aureus bacteria model using a UVA/blue light source. Films based on the 2,6-naphthalenedicarboxylic acid linker significantly reduced the number of viable bacteria by 99.9%, while no apparent activity was observed for the two other photoactive systems. Our work thus provides evidence that the MLD technique is a suitable tool to produce high-quality novel materials for possible applications in antimicrobial PDT, however it requires a careful selection of aromatic ligands used to construct photoactive materials.

Controlling the shape morphology of origami-inspired photoresponsive hydrogels.

The concept of origami has influenced the development of responsive materials that can mimic complex functions performed by living organisms. An ultimate goal is to discover and design soft materials that can be remotely actuated into diverse structures. To achieve this goal, we design and synthesize here a light-responsive spiropyran hydrogel system that can display dynamic shape changes upon irradiation with local light. We use a continuum polymer model to analyze the behavior of the constructed photoactive hydrogel, which is in good agreement with the experimental results. We explore different buckling modalities and patterns in a different range of parameters. The synthesis and fabrication of these materials demonstrate that the theoretical model can be used to drive the development of responsive photoactive systems.

Computational Design and Properties Elucidation of New (Fapbi3)1-X-Y(Mapbbr3)Y(Cspbbr3)X Photoactive Systems for Their Application in Perovskite Solar Cells

Computational Design and Properties Elucidation of New (Fapbi3)1-X-Y(Mapbbr3)Y(Cspbbr3)X Photoactive Systems for Their Application in Perovskite Solar Cells

Air‐Processed Organic Photovoltaics for Outdoor and Indoor Use Based upon a Tin Oxide‐Perylene Diimide Electron Transporting Bilayer

AbstractEfficient organic photovoltaics (OPV) based on SnO2 | perylene diimide (PDI) bilayer as an electron transport layer (ETL) is fabricated and tested in an ambient environment. The PTQ10:Y6 photoactive system is used as the primary bulk‐heterojunction. Without any surface treatment, the power conversion efficiency (PCE) of SnO2‐based OPV devices is 1.5%. Treating the SnO2 nano‐particles with UV‐ozone and then applying a layer of N‐annulated PDI with a functional NH bond (PDIN‐H) on top increase device PCEs to 9.2%. For indoor applications, the OPV device PCE rises from 8.1% to 12.3% when PDIN‐H is employed on SnO2 and tested under low light conditions, without the need for light soaking. The SnO2 | PDIN‐H ETL bilayer is slot‐die coated and corresponding OPV devices have a PCE of 7.9%, demonstrating utility for OPV scale‐up. The hybrid ETL is tested with other photoactive systems employing Y6, Y7, and IDIC as acceptors, as well as PM6 donor, and all these cases yield OPV devices with improved PCE when compared to OPV devices with SnO2‐only ETLs. These results show the successful implementation of SnO2 | PDIN‐H as an ETL for OPV.

Recent Advances Towards Sustainable Materials and Processes for Energy Conversion and Storage

Recent Advances Towards Sustainable Materials and Processes for Energy Conversion and Storage

A Brief History of Photoactive Interlocked Systems Assembled by Transition Metal Template Synthesis

More than three decades of research efforts have yielded powerful methodologies based on transition metal template-directed syntheses for the assembly of a huge number of interlocked systems, molecular knots, machines and synthesizers. Such template techniques have been applied in the preparation of mechanically linked electron donor–acceptor artificial photosynthetic models. Consequently, synthetic challenging photoactive rotaxanes and catenanes have been reported, in which the chromophores are not covalently linked but are still associated with undergoing sequential energy (EnT) and electron transfer (ET) processes upon photoexcitation. Many interlocked photosynthetic models produce highly energetic, but still long-living charge separated states (CSS). The present work describes in a historical perspective some key advances in the field of photoactive interlocked systems assembled by transition metal template techniques, which illustrate the usefulness of rotaxanes and catenanes as molecular scaffolds to organize electron donor–acceptor groups. The effects of molecular dynamics, molecular topology, as well as the role of the transition metal ion used as template species, on the thermodynamic and kinetic parameters of the photoinduced energy and electron transfer processes in the interlocked systems are also discussed.

PEDOT:PSS‐Free Polymer Non‐Fullerene Polymer Solar Cells with Efficiency up to 18.60% Employing a Binary‐Solvent‐Chlorinated ITO Anode

AbstractDespite the tremendous development of different high‐performing photovoltaic systems in non‐fullerene polymer solar cells (PSCs), improving their performance is still highly demanding. Herein, an effective and compatible strategy, i.e., binary‐solvent‐chlorinated indium tin oxide (ITO) anode, is presented to improve the device performance of the state‐of‐the‐art photoactive systems. Although both ODCB (1,2‐dichlorobenzene) solvent‐ and ODCB:H2O2 (hydrogen peroxide) co‐solvent‐chlorinated ITO (ITO‐Cl‐ODCB and ITO‐Cl‐ODCB:H2O2) show similar optical transmittance, electrical conductivities, and work function values, ITO‐Cl‐ODCB:H2O2 exhibits higher Cl surface coverage and more suitable surface free energy close to the poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐buffered ITO anode (ITO/PEDOT:PSS). As a direct consequence, the performance of ITO‐Cl‐ODCB‐based PBDB‐T‐2F:BTP‐eC9:PC71BM PSCs is comparable as the bare ITO‐based devices. In contrast, the performance of ITO‐Cl‐ODCB:H2O2‐based devices with both small and the scaled‐up areas significantly surpass the ITO/PEDOT:PSS‐based devices. Furthermore, detailed experimental studies are conducted linking optical property, blend morphology, and physical dynamics to find the reasons for the performance difference. By applying the ITO‐Cl‐ODCB:H2O2 anode to six other photovoltaic systems, the device efficiencies are enhanced by 3.6–6.2% relative to those of the ITO/PEDOT:PSS‐based control devices, which validates its great application potential of co‐solvent‐modified ITO anode employed into PEDOT:PSS‐free PSCs.

Effect of Silver Modification on the Photoactivity of Titania Coatings with Different Pore Structures.

Nanostructured photoactive systems are promising for applications such as air and water purification, including self-cleaning coatings. In this study, mesoporous TiO2 sol-gel coatings with different pore structures were prepared and modified with silver by two methods: the “mixing” method by adding AgNO3 to the precursor sol, and the “impregnation” method by immersing the samples in AgNO3 solution (0.03 and 1 M) followed by heat treatment. Our aim was to investigate the effects that silver modification has on the functional properties (e.g., those that are important for self-cleaning coatings). Transmittance, band gap energy, refractive index, porosity and thickness values were determined from UV-Vis spectroscopy measurements. Silver content and structure of the silver modified samples were characterized by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, High-resolution transmission electron microscopy and Energy Dispersive X-ray Spectrometry elemental mapping measurements. Wettability properties, including photoinduced wettability conversion behavior were investigated by water contact angle measurements. Photoactivity was studied under both UV and visible light with rhodamine 6G and methylene blue dye molecules, at the liquid–solid and air–solid interfaces modeling the operating conditions of self-cleaning coatings. Samples made with “impregnation” method showed better functional properties, in spite of their significantly lower silver content. The pore structure influenced the Ag content achieved by the “impregnation” method, and consequently affected their photoactivity.

Strategies for coupling photon-upconverting nanoparticles with photoactive protein therapeutics

Nanomedicine is a rapidly advancing field as capabilities in nanoscale materials, devices, and sensing grow. Biocompatible nanoparticles have made their way into the pharmaceutical and biomedical market in imaging, diagnosis, targeted drug delivery, and even repair. Similarly, protein therapeutics show promise for their unique combination of high biospecificity and diverse function. This brief perspective explores the merging of these two fields via light-controlled methods mediated by photon-upconverting nanoparticles. The framework of three photoactive protein therapeutic systems will be explored for their integration with upconverting nanoparticles.

Utilizing 3,4-ethylenedioxythiophene (EDOT)-bridged non-fullerene acceptors for efficient organic solar cells

A rational design of efficient low-band-gap non-fullerene acceptors (NFAs) for high-performance organic solar cells (OSCs) remains challenging; the main constraint being the decrease in the energy level of the lowest unoccupied molecular orbitals (LUMOs) as the bandgap of A-D-A-type NFAs decrease. Therefore, the short current density (Jsc) and open-circuit voltage (Voc) result in a trade-off relationship, making it difficult to obtain efficient OSCs. Herein, three NFAs (IFL-ED-4F, IDT-ED-4F, and IDTT-ED-2F) were synthesized to address the above-mentioned issue by introducing 3,4-ethylenedioxythiophene (EDOT) as a π-bridge. These NFAs exhibit relatively low bandgaps (1.67, 1.42, and 1.49 eV, respectively) and upshifted LUMO levels (-3.88, −3.84, and −3.81 eV, respectively) compared with most reported low-band-gap NFAs. Consequently, the photovoltaic devices based on IDT-ED-4F blended with a PBDB-T donor polymer showed the best power conversion efficiency (PCE) of 10.4% with a high Jsc of 22.1 mA cm−2 and Voc of 0.884 V among the examined NFAs. In contrast, IDTT-ED-4F, which was designed with an asymmetric structure of the D-π-A type, showed the lowest efficiency of 1.5% owing to the poor morphology and charge transport properties of the binary blend. However, when this was introduced as the third component of the PM6:BTP-BO-4Cl, complementary absorption and cascade energy-level alignment between the two substances could be achieved. Surprisingly, the IDTT-ED-4F-based ternary blend device not only improved the Jsc and Voc, but also achieved a PCE of 15.2%, which is approximately 5.3% higher than that of the reference device with a minimized energy loss of 0.488 eV. In addition, the universality of IDTT-ED-2F as a third component was effectively demonstrated in other photoactive systems, specifically, PM6:BTP-eC9 and PTB7-Th:IEICO-4F. This work facilitates a better understanding of the structure–property relationship for utilizing efficient EDOT-bridged NFAs in high-performance OSC applications.

Theoretical characterization of photoactive molecular systems based on BODIPY-derivatives for the design of organic solar cells

The search for high-efficiency narrow-band donor materials to improve the short-circuit current density (Jsc) of organic solar cells, a series of small molecules based in Bodipy-Triphenylamine were characterized using density functional theory (DFT) and time-dependent (TD-DFT) calculations. According to the energy of the exciton driving force they have the appropriate energy levels to match PC61BM. The properties affecting the open circuit voltage (Voc), Jsc and the fill factor (FF) were investigated by calculating the geometric structures, the boundary molecular orbital energy levels, absorption spectra, light collection efficiencies, charge transfer rates, and exciton binding energies. The results show that the BTPA III system has a lower LUMO level, high absorption efficiency, and exciton dissociation than other molecular systems, facilitating the improvement of Voc,Jsc and FF. Finally, BTPA III would be the most promising of this series of donors and further increase the efficiency of the device.

Efficient and Selective Visible-Light-Driven Oxidative Coupling of Amines to Imines in Air over CdS@Zr-MOFs.

Construction of porous photoactive MOF-based composite systems is regarded as one of the most effective strategies to improve light harvesting, increase the surface area, provide plenty of exposed active sites, and promote the reduction and oxidation abilities of some organic photocatalytic reactions. Herein, we synthesized porous CdS@Zr-MOF photocatalysts based on the representative photocatalyst CdS and crystalline Zr-MOFs, such as MOF-808, NU-1000, and PCN-222, to illustrate their excellent photocatalytic performance for the synthesis of imines in air. The morphology and composition of these photocatalysts were investigated by X-ray powder diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-AES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), indicating their crystallinity, high porosity, and interfacial interaction between constituents. Compared with individual components, these porous CdS@Zr-MOF composites could remarkably promote photocatalytic activity for the oxidative coupling of amines under air and visible-light conditions. The photocatalytic reaction showed broad substrate suitability. More importantly, the conversion yield reached up to 95% for the inactive aliphatic amines, and imines were formed as the single product. The improvement of the photocatalytic performance of CdS@Zr-MOF composites can be mainly ascribed to their high surface areas, more exposed active sites, excellent dispersion of CdS, and special porous photocatalytic systems, which tune the band gap, broaden the light response range, and facilitate the carrier separation.

Bifunctional Role of Zn in α-Fe <sub>2</sub>O <sub>3</sub> Boosts the Photoelectrochemical Water Oxidation: Zn <sup>2+</sup> Doping and Catalytic Effect

The serious recombination of photocarriers in hematite (α-Fe2O3) is the intrinsic limitation that lessens the photoelectrochemical (PEC) performance of water splitting. For the first time, the n-type Zn doped α-Fe2O3 nanowire was successfully fabricated and used as the photoanode for PEC water splitting. The Zn doped α-Fe2O3 demonstrated enhanced PEC performance over the single α-Fe2O3, the photocurrent density increased up to 0.88 mA/cm2(1.23 VRHE), which showed a 44-fold increase than the α-Fe2O3 and accompanied by 300 mV negative shift of onset potential. The coupled electrochemical measurements and density functional theory calculations (DFT) revealed the bifunctional role of Zn doping: increasing the carrier density and accelerating oxygen evolution kinetics simultaneously, by which the charge separation efficiency improved significantly. This work provides a deep understanding of the role of Zn in the α-Fe2O3 photoanodes and the strategy could be extended to other photoactive systems.

The molecular basis of spectral tuning in blue- and red-shifted flavin-binding fluorescent proteins

Photoactive biological systems modify the optical properties of their chromophores, known as spectral tuning. Determining the molecular origin of spectral tuning is instrumental for understanding the function and developing applications of these biomolecules. Spectral tuning in flavin-binding fluorescent proteins (FbFPs), an emerging class of fluorescent reporters, is limited by their dependency on protein-bound flavins, whose structure and hence electronic properties cannot be altered by mutation. A blue-shifted variant of the plant-derived improved light, oxygen, voltage FbFP has been created by introducing a lysine within the flavin-binding pocket, but the molecular basis of this shift remains unconfirmed. We here structurally characterize the blue-shifted improved light, oxygen, voltage variant and construct a new blue-shifted CagFbFP protein by introducing an analogous mutation. X-ray structures of both proteins reveal displacement of the lysine away from the chromophore and opening up of the structure as instrumental for the blue shift. Site saturation mutagenesis and high-throughput screening yielded a red-shifted variant, and structural analysis revealed that the lysine side chain of the blue-shifted variant is stabilized close to the flavin by a secondary mutation, accounting for the red shift. Thus, a single additional mutation in a blue-shifted variant is sufficient to generate a red-shifted FbFP. Using spectroscopy, X-ray crystallography, and quantum mechanics molecular mechanics calculations, we provide a firm structural and functional understanding of spectral tuning in FbFPs. We also show that the identified blue- and red-shifted variants allow for two-color microscopy based on spectral separation. In summary, the generated blue- and red-shifted variants represent promising new tools for application in life sciences.

Synergy of Electrostatic and π-π Interactions in the Realization of Nanoscale Artificial Photosynthetic Model Systems.

In the scientific race to build up photoactive electron donor‐acceptor systems with increasing efficiencies, little is known about the interplay of their building blocks when integrated into supramolecular nanoscale arrays, particularly in aqueous environments. Here, we describe an aqueous donor‐acceptor ensemble whose emergence as a nanoscale material renders it remarkably stable and efficient. We have focused on a tetracationic zinc phthalocyanine (ZnPc) featuring pyrenes, which shows an unprecedented mode of aggregation, driven by subtle cooperation between electrostatic and π–π interactions. Our studies demonstrate monocrystalline growth in solution and a symmetry‐breaking intermolecular charge transfer between adjacent ZnPcs upon photoexcitation. Immobilizing a negatively charged fullerene (C60) as electron acceptor onto the monocrystalline ZnPc assemblies was found to enhance the overall stability, and to suppress the energy‐wasting charge recombination found in the absence of C60. Overall, the resulting artificial photosynthetic model system exhibits a high degree of preorganization, which facilitates efficient charge separation and subsequent charge transport.

Ultrafast Spectroscopy of Photoactive Molecular Systems from First Principles: Where We Stand Today and Where We Are Going.

Computational spectroscopy is becoming a mandatory tool for the interpretation of the complex, and often congested, spectral maps delivered by modern non-linear multi-pulse techniques. The fields of Electronic Structure Methods, Non-Adiabatic Molecular Dynamics, and Theoretical Spectroscopy represent the three pillars of the virtual ultrafast optical spectrometer, able to deliver transient spectra in silico from first principles. A successful simulation strategy requires a synergistic approach that balances between the three fields, each one having its very own challenges and bottlenecks. The aim of this Perspective is to demonstrate that, despite these challenges, an impressive agreement between theory and experiment is achievable now regarding the modeling of ultrafast photoinduced processes in complex molecular architectures. Beyond that, some key recent developments in the three fields are presented that we believe will have major impacts on spectroscopic simulations in the very near future. Potential directions of development, pending challenges, and rising opportunities are illustrated.

A Cost‐Effective, Aqueous‐Solution‐Processed Cathode Interlayer Based on Organosilica Nanodots for Highly Efficient and Stable Organic Solar Cells

The performance and industrial viability of organic photovoltaics are strongly influenced by the functionality and stability of interface layers. Many of the interface materials most commonly used in the lab are limited in their operational stability or their materials cost and are frequently not transferred toward large-scale production and industrial applications. In this work, an advanced aqueous-solution-processed cathode interface layer is demonstrated based on cost-effective organosilica nanodots (OSiNDs) synthesized via a simple one-step hydrothermal reaction. Compared to the interface layers optimized for inverted organic solar cells (i-OSCs), the OSiNDs cathode interlayer shows improved charge carrier extraction and excellent operational stability for various model photoactive systems, achieving a remarkably high power conversion efficiency up to 17.15%. More importantly, the OSiNDs' interlayer is extremely stable under thermal stress or photoillumination (UV and AM 1.5G) and undergoes no photochemical reaction with the photoactive materials used. As a result, the operational stability of inverted OSCs under continuous 1 sun illumination (AM 1.5G, 100mW cm-2 ) is significantly improved by replacing the commonly used ZnO interlayer with OSiND-based interfaces.