Photo-Responsive Hydrogen-Bonded Molecular Networks Capable of Retaining Crystalline Periodicity after Isomerization.

The molecular conformation, crystalline morphology, and properties of photochromic organic crystals can be controlled through photoirradiation, making them promising candidates for functional organic materials. However, photochromic porous molecular crystals with a networked framework structure are rare due to the difficulty in maintaining space that allows for photo-induced molecular motion in the crystalline state. This study describes a photo-responsive single crystal based on hydrogen-bonded (H-bonded) network of dihydrodimethylbenzo[e]pyrene derivative 4BDHP. A crystal composed of H-bonded undulate layers, 4BDHP-2, underwent photo-isomerization in the crystalline state due to loose stacking of the layers. Particularly, enantio-pure crystal (S,S)-4BDHP-2 allowed to reveal the structure of the photoisomerized crystal, in which the closed form (4BDHP) and open form (4CPD) were arranged alternately with keeping crystalline periodicity, although side reactions were also implied. The present proof-of-concept system of a photochromic framework that retains crystalline periodicity after photo-isomerization may provide new light-driven porous functional materials.

Polymorphism of Two-Dimensional Semiconducting Coordination Polymers: Impact of a Lead-Sulfur Network on Photoconductivity.

Sulfur-coordinated coordination polymers (S-CPs) have unique optoelectrical properties that originate from infinite M-S bond networks. In this study, we synthesized and characterized two polymorphs of a two-dimensional (2D) Pb(II) S-CP with a formula of [Pb(tzdt)(OAc)] (Htzdt=1,3-thiazolidine-2-thione, OAc=acetate). Our findings revealed that the thermodynamic product (KGF-26) possesses quasi-2D (-Pb-S-)n layers with weak nonbonded Pb-S bonds, whereas the kinetic product (KGF-27) has intrinsic 2D (-Pb-S-)n layers with Pb-S bonds. The results of time-resolved microwave conductivity measurements and first-principles calculations confirmed that KGF-27 exhibits higher photoconductivity than KGF-26, which establishes that the inorganic (-Pb-S-)n networks with Pb-S bonds are crucial for achieving high photoconductivity. This is the first experimental demonstration of the impact of the (-M-S-)n networks in S-CPs on photoconductivity through the comparison of crystal polymorphisms.

Modification of Visible-Light-Responsive Pb2Ti2O5.4F1.2 with Metal Oxide Cocatalysts to Improve Photocatalytic O2 Evolution toward Z-Scheme Overall Water Splitting.

The development of a highly active photocatalyst for visible-light water splitting requires a high-quality semiconductor material and a cocatalyst, which promote both the migration of photogenerated charge carriers and surface redox reactions. In this work, a cocatalyst was loaded onto an oxyfluoride photocatalyst, Pb2Ti2O5.4F1.2, to improve the water oxidation activity. Among the metal oxides examined as cocatalysts, RuO2 was found to be the most suitable, and the O2 evolution activity depended on the preparation conditions for Ru/Pb2Ti2O5.4F1.2. The highest activity was obtained with RuCl3-impregnated Pb2Ti2O5.4F1.2 heated under a flow of H2 at 523 K. The H2-treated Ru/Pb2Ti2O5.4F1.2 showed an O2 evolution rate an order of magnitude higher than those for the analogues without the H2 treatment (e. g., RuO2/Pb2Ti2O5.4F1.2). Physicochemical analyses by X-ray absorption fine-structure spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and time-resolved microwave conductivity measurements indicated that the optimized photocatalyst contained partially reduced RuO2 species with a particle size of ~5 nm. These partially reduced species effectively trapped the photogenerated charge carriers and promoted the oxidation of water into O2. The optimized Ru/Pb2Ti2O5.4F1.2 could function as an O2-evolving photocatalyst in Z-scheme overall water splitting, in combination with an Ru-loaded, Rh-doped SrTiO3 photocatalyst.

Water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change.

Novel water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles, having dibenzophenazine as the acceptor and heteroatom-bridged amphiphilic diarylamines as the donors, have been developed. The materials displayed a distinct photoluminescence color change in response to humidity in a poly(vinylalcohol) matrix.

Correction: Water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change.

Correction for 'Water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change' by Tomoya Enjou et al., Chem. Commun., 2024, https://doi.org/10.1039/d3cc05749f.

Metal-free carbazole-thiophene photosensitizers designed for a dye-sensitized H2-evolving photocatalyst in Z-scheme water splitting.

Dye-sensitized photocatalysts with molecular dyes and widegap semiconductors have attracted attention because of their design flexibility, for example, tunable light absorption for visible-light water splitting. Although organic dyes are promising candidates as metal-free photosensitizers in dye-sensitized photocatalysts, their efficiency in H2 production has far been unsatisfactory compared to that of metal-complex photosensitizers, such as Ru(II) tris-diimine-type complexes. Here, we demonstrate the substantial improvement of carbazole-thiophene-based dyes used for dye-sensitized photocatalysts through systematic molecular design of the number of thiophene rings, substituents in the thiophene moiety, and the anchoring group. The optimized carbazole-thiophene dye-sensitized layered niobate exhibited a quantum efficiency of 0.3% at 460 nm for H2 evolution using a redox-reversible I- electron donor, which is six-times higher than that of the best coumarin-based metal-free dye reported to date. The dye-sensitized photocatalyst also facilitated overall water splitting when combined with a WO3-based O2-evolving photocatalyst and an I3-/I- redox shuttle mediator. The present metal-free dye provided a high dye-based turnover frequency for water splitting, comparable to that of the state-of-the-art Ru(II) tris-diimine-type photosensitizer, by simple adsorption onto a layered niobate. Thus, this study highlights the potential of metal-free organic dyes with appropriate molecular designs for the development of efficient water splitting.

Engineering of CdS-chain arrays assembled through S⋯S interactions in 1D semiconductive coordination polymers.

One-dimensional (1D) Cd(II) coordination polymers [Cd(x-SPhOMe)2]n (x = ortho, meta, and para; HSPhOMe = methoxybenzenethiol) containing inorganic 1D (-Cd-S-)n chains were synthesized. Among these, the KGF-31 polymer bearing para-SPhOMe featured a three-strand chain structure assembled via interchain S⋯S interactions and exhibited high photoconductivity and longevity.

Supramolecular nanosheet formation-induced photosensitisation mechanism change of Rose Bengal dye in aqueous media.

Development of two-dimensional materials and exploration of their functionalities are significant challenges due to their potential. In this study, we successfully fabricated a supramolecular nanosheet composed of amphiphilic Rose Bengal dyes in an aqueous medium. Furthermore, we elucidated a distinct change in the photosensitisation mechanism induced by nanosheet formation.

Nonclassical Crystal Growth of Supramolecular Polymers in Aqueous Medium.

A mechanistic understanding of the principles governing the hierarchical organization of supramolecular polymers offers a paradigm for tailoring synthetic molecular architectures at the nano to micrometric scales. Herein, the unconventional crystal growth mechanism of a supramolecular polymer of superbenzene(coronene)-diphenylalanine conjugate (Cr-FFOEt ) is demonstrated. 3D electron diffraction (3D ED), a technique underexplored in supramolecular chemistry, is effectively utilized to gain a molecular-level understanding of the gradual growth of the initially formed poorly crystalline hairy, fibril-like supramolecular polymers into the ribbon-like crystallites. The further evolution of these nanosized flat ribbons into microcrystals by oriented attachment and lateral fusion is probed by time-resolved microscopy and electron diffraction. The gradual morphological and structural changes reveal the nonclassical crystal growth pathway, where the balance of strong and weak intermolecular interactions led to a structure beyond the nanoscale. The role of distinct π-stacking and H-bonding interactions that drive the nonclassical crystallization process of Cr-FFOEt supramolecular polymers is analyzed in comparison to analogous molecules, Py-FFOEt and Cr-FF forming helical and twisted fibers, respectively. Furthermore, the Cr-FFOEt crystals formed through nonclassical crystallization are found to improve the functional properties.

Exploration of Solution-Processed Bi/Sb Solar Cells by Automated Robotic Experiments Equipped with Microwave Conductivity.

Solution-processed inorganic solar cells with less toxic and earth-abundant elements are emerging as viable alternatives to high-performance lead-halide perovskite solar cells. However, the wide range of elements and process parameters impede the rapid exploration of vast chemical spaces. Here, we developed an automated robot-embedded measurement system that performs photoabsorption spectroscopy, optical microscopy, and white-light flash time-resolved microwave conductivity (TRMC). We tested 576 films of quaternary element-blended wide-bandgap Cs-Bi-Sb-I semiconductors with various compositions, organic salt additives (MACl, FACl, MAI, and FAI, where MA and FA represent methylammonium and formamidinium, respectively), and thermal annealing temperatures. Among them, we found that the maximum power conversion efficiency (PCE) was 2.36%, which is significantly higher than the PCE of 0.68% for a reference film without an additive. Machine learning (ML) and statistical analyses revealed significant features and their relationships with TRMC transients, thereby demonstrating the advantages of combining ML and automated experiments for the high-throughput exploration of photovoltaic materials.

Complexation study of a 1,3-phenylene-bridged cyclic hexa-naphthalene with fullerenes C60 and C70 in solution and 1D-alignment of fullerenes in the crystals.

To investigate the host ability of a simple macrocycle, 1,3-phenylene-bridged naphthalene hexamer N6, we evaluated the complexation of N6 with fullerenes in toluene and in the crystals. The complexes in the solid-state demonstrate the one-dimensional alignment of fullerenes. The single-crystals of the C60@N6 composite have semiconductive properties revealed by photoconductivity measurements.

Perovskite Solar Cell Using Isonicotinic Acid as a Gap-Filling Self-Assembled Monolayer with High Photovoltaic Performance and Light Stability.

High photovoltaic performance and light stability are required for the practical outdoor use of lead-halide perovskite solar cells. To improve the light stability of perovskite solar cells, it is effective to introduce a self-assembled monolayer (SAM) between the carrier transport layer and the perovskite layer. Several alternative approaches in their molecular design and combination with multiple SAMs support high photovoltaic conversion efficiency (PCE). Herein, we report a new structure for improving both PCE and light stability, in which the surface of an electron transport layer (ETL) was modified by combining a fullerene-functionalized self-assembled monolayer (C60SAM) and a suitable gap-filling self-assembled monolayer (GFSAM). Small-sized GFSAMs can enter the gap space of the C60SAM and terminate the unterminated sites on the ETL surface. The best GFSAM in this study was formed using an isonicotinic acid solution. After a light stability test for 68 h at 50 °C under 1 sun illumination, the best cell with C60SAM and GFSAM showed a PCE of 18.68% with a retention rate of over 99%. Moreover, following outdoor exposure for six months, the cells with C60SAM and GFSAM exhibited almost unchanged PCE. From the valence band spectra of the ETLs obtained using hard X-ray photoelectron spectroscopy, we confirmed a decrease in the offset at the ETL/perovskite interface owing to the additional GFSAM treatment on the C60SAM-modified ETL surface. Time-resolved microwave conductivity measurements demonstrated that the additional GFSAM improved electron extraction at the C60SAM-modified ETL/perovskite interface.

Alkyl-C60 liquid electrets as deformable mechanoelectric generators.

Special attention is being paid to the potential applicability of various soft electronics in deformable/wearable devices. These devices must be constantly connected to energy sources to ensure their uninterrupted operation. Electrets, which are capable of retaining quasi-permanent electric charges inside or on the surface of materials, are expected to be a battery-less power source. Here, we present a strategy for harvesting the charges in alkyl-C60 liquids. Suitable substitution of bulky yet flexible branched long-alkyl chains generated C60-mono-adducts and regioisomeric bis-adducts as room-temperature solvent-free liquids. These alkyl-C60 liquids were negatively poled by the corona-discharging and soaked in nylon fabric. The liquid of the C60 bis-adduct exhibited better charge retention in comparison to the liquid of the C60 mono-adduct. This suggests that the bulky long-alkyl chains provided proper insulation for the C60 core and charge trapping in the liquid. This charge-trapping behaviour and the inherent fluidity of the alkyl-C60 liquids enabled their fabrication into deformable mechanoelectric generator (MEG) devices. The MEG exhibited applicability as a deformable micropower source or vibration sensor by generating output voltage pulses even under folded/twisted/rolled conditions. The alkylated-liquid-based MEGs worked at frequencies similar to human body motion, showing promising potential for body motion sensors and healthcare applications.

Expanded [2,1][n]Carbohelicenes with 15- and 17-Benzene Rings.

Expanded carbohelicenes with structures fused to 15- and 17-benzene were successfully synthesized. Establishing a new synthetic strategy is crucial to realize the development of longer expanded [2,1][n]helicenes with a kekulene-like projection drawing structure. This article describes the sequential integration of the π-elongating Wittig reaction of functionalized phenanthrene units and ring-fusing Yamamoto coupling for the synthesis of [2,1][15]helicenes and [2,1][17]helicenes. X-ray crystallographic structures, photophysical properties, and density functional theory (DFT) calculations revealed the unique characteristics of the synthesized expanded helicenes. Furthermore, because of the high enantiomerization barrier derived from a wide-range intrahelix π-π interaction, the optical resolution of [2,1][17]helicene was successfully achieved, and chiroptical properties such as circular dichroism and circularly polarized luminescence were elucidated for the first time as enantiomers of pristine [2,1][n]helicene core.

Machine learning of atomic force microscopy images of organic solar cells.

The bulk heterojunction structures of organic photovoltaics (OPVs) have been overlooked in their machine learning (ML) approach despite their presumably significant impact on power conversion efficiency (PCE). In this study, we examined the use of atomic force microscopy (AFM) images to construct an ML model for predicting the PCE of polymer : non-fullerene molecular acceptor OPVs. We manually collected experimentally observed AFM images from the literature, applied data curing and performed image analyses (fast Fourier transform, FFT; gray-level co-occurrence matrix, GLCM; histogram analysis, HA) and ML linear regression. The accuracy of the model did not considerably improve even by including AFM data in addition to the chemical structure fingerprints, material properties and process parameters. However, we found that a specific spatial wavelength of FFT (40-65 nm) significantly affects PCE. The GLCM and HA methods, such as homogeneity, correlation and skewness expand the scope of image analysis and artificial intelligence in materials science research fields.

Precise Control of the Molecular Arrangement of Organic Semiconductors for High Charge Carrier Mobility.

Organic semiconductors are well-known to exhibit high charge carrier mobility based on their spread of the π-orbital. In particular, the π-orbital overlap between neighboring molecules significantly affects their charge carrier mobility. This study elucidated the direct effect of subtle differences in the π-orbital overlap on charge carrier mobility, by precisely controlling only molecular arrangements without any chemical modifications. We synthesized disulfonic acid composed of a [1]benzothieno[3,2-b][1]benzothiophene (BTBT) moiety, and prepared organic salts with four butylamine isomers. Regardless of the type of butylamine combined, electronic states of the constituent BTBT derivative were identical, and all BTBT arrangements were edge-to-face herringbone-type. However, depending on the difference of steric hindrance, center-to-center distances and dihedral angles between neighboring BTBT moieties slightly varied. Despite a similar arrangement, the photoconductivity of four organic salts differed by a factor of approximately two. Additionally, theoretical charge carrier mobilities from their crystal structures exhibited a strong correlation with their photoconductivity.

Elucidation of a Photothermal Energy Conversion Mechanism in Hydrogenated Molybdenum Suboxide: Interplay of Trapped Charges and Their Dielectric Interactions.

Hydrogenated molybdenum suboxide (HxMoO3-y) is a promising photothermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/HxMoO3-y composite. The charge recombination of H2-reduced Pt/HxMoO3-y was 2-3 orders of magnitude faster than that of Pt/MoO3, indicating efficient PEC. A complex photoconductivity study revealed that Pt/HxMoO3-y has two types of trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, depending on the reduction temperature. Pt/HxMoO3-y reduced at 100 °C exhibited a dominant NPE owing to the electrical interaction of trapped charges with the surrounding ions and/or OH base. This polaronic trapped state retarded the PEC process. We found Pt/HxMoO3-y reduced at 200 °C to be optimal owing to the balanced suppression of the NPE and charge diffusion. This is the first report revealing the charge dynamics in hydrogenated metal oxides and their impacts on PEC processes.

Correction: Phosphaacene as a structural analogue of thienoacenes for organic semiconductors.

Correction for 'Phosphaacene as a structural analogue of thienoacenes for organic semiconductors' by Kyohei Matsuo et al., Chem. Commun., 2022, 58, 13576-13579, https://doi.org/10.1039/D2CC05122B.

Supramolecular Recognition within a Nanosized "Buckytrap" That Exhibits Substantial Photoconductivity.

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C70. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2•C60)n or (2•C70)n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H2O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 104 M-1 and (4.3 ± 0.9) × 104 M-1 to be calculated for C60 and C70, respectively. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (ϕ∑µ), increases upon fullerene inclusion (e.g., ϕ∑µ = 1.53 × 10-4 cm2 V-1 s-1 for C60⊂(1a)2 and ϕ∑µ = 1.45 × 10-4 cm2 V-1 s-1 for C70⊂(1a)2 vs ϕ∑µ = 2.49 × 10-5 cm2 V-1 s-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.