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We elucidate that the peculiar segregation behavior of indium have a critical contribution to achieving unprecedented dielectric properties for a new class of high-reliability ceramic capacitors.

π-Extended ullazines were obtained using complementary synthetic approaches based on direct arylation and cycloaddition reactions, respectively. Their strong fluorescence can be tuned by appropriate modifications of substitution and edge expansion.

Photo-induced charge carrier dynamics over a wide time domain from sub-nanoseconds to microseconds, via time-correlated single photon counting and flash photolysis time-resolved microwave conductivity measurements.

Recently, Baird (anti)aromaticity has been referred to as a description of excited-state (anti)aromaticity. With the term of Baird's rule, recent studies have intensively verified that the Hückel aromatic [4

Correction for ‘Unveiling of interstice-occupying dopant segregation at grain boundaries in perovskite oxide dielectrics for a new class of ceramic capacitors’ by Ji-Sang An et al., Energy Environ. Sci., 2023, https://doi.org/10.1039/d2ee03152c.

Nanostructured materials offer the potential to drive future developments and applications of electrochemical devices, but are underutilized because their nanoscale cavities can impose mass transfer limitations that constrain electrochemical signal generation. Here, we report a new signal-generating mechanism that employs a molecular redox capacitor to enable nanostructured electrodes to amplify electrochemical signals even without an enhanced reactant mass transfer. The surface-tethered molecular redox capacitor engages diffusible reactants and products in redox-cycling reactions with the electrode. Such redox-cycling reactions are facilitated by the nanostructure that increases the probabilities of both reactant-electrode and product-redox-capacitor encounters (i.e., the nanoconfinement effect), resulting in substantial signal amplification. Using redox-capacitor-tethered Au nanopillar electrodes, we demonstrate improved sensitivity for measuring pyocyanin (bacterial metabolite). This study paves a new way of using nanostructured materials in electrochemical applications by engineering the reaction pathway within the nanoscale cavities of the materials.

We have previously developed CsPbBr3 NCs exhibiting a tremendously high photoluminescence (PL) and structural stability by adding ZnBr2. However, understanding of these outstanding properties is lacking due to the absence of spectroscopic analyses, such as spectral or dynamical characteristics. In this work, we conducted a comparative analysis of photophysical properties for conventional-CsPbBr3 NCs and ZnBr2–CsPbBr3 NCs. First, we analyzed the blinking traces by comparing the single crystal PL intermittency. It has been found that the PL quantum yield of CsPbBr3 NCs is gradually decreasing at the ensemble level, resulting from a significant activation of the Auger-induced blinking. Furthermore, the time-resolved TA dynamics supports the fact that Auger-type energy transfer accelerates the hot carrier cooling time, and thereby the Auger-induced blinking behavior in the band-edge state becomes dominant over time. Here, ZnBr2–CsPbBr3 NCs showed a low multiexciton Auger amplitude and therefore had a stable PL emission compared with conventional-CsPbBr3 NCs. Finally, we suggest that both NCs differ in intraband spacing possibly due to capping ligands, finally leading to a suppressed Auger process and higher stability for ZnBr2–CsPbBr3 NCs.

A boronic acid functionalized phthalocyanine displays aggregation-enhanced reactive oxygen species (ROS) generation and excellent photodynamic antibacterial activity., Most existing photosensitizers (e.g., porphyrins) are often aggregated in aqueous solution because of their large conjugated molecular structures. This aggregation usually results in a lack or low levels of reactive oxygen species (ROS) generation due to aggregation-caused quenching, which severely hampers the application of photosensitizers in photodynamic therapy (PDT). Herein, we make an interesting finding that a boronic acid-functionalized phthalocyanine (PcN4-BA) displays an uncommon phenomenon, an aggregation-enhanced photodynamic effect. The combination of the ability to form uniform nanostructured self-assemblies in water, highly efficient ROS generation and boronic acid-induced targeting give PcN4-BA excellent performances in antimicrobial PDT.

A diindenophenanthrene biradicaloid, formally derived from Chichibabin's hydrocarbon, is obtained in a short, scalable synthesis. The present system is electron-rich and devoid of conjugated substituents, and still exhibits very good stability under ambient conditions. The introduction of the diindeno[1,2-a:2′,1′-i] phenanthrene ring framework results in a singlet biradicaloid system with an easily accessible triplet state (ΔES–T = −1.30 kcal mol−1) and a small electronic bandgap (1.39 V). The stability limits of the title hydrocarbon were explored systematically in the solid state, to reveal an unusual thermally initiated hydrogen-scrambling oligomerization process.

A sponge-based surface-enhanced Raman scattering (SERS) sensor composed of silver nanowires (AgNWs) coated with hydrophobic hexagonal boron nitride (hBN) was prepared for the simultaneous separation and detection of organic pollutants. AgNWs adhered on a melamine-sponge surface formed a high density of hotspots for Raman signal enhancement, and hydrophobic hBN coated on AgNWs functioned as an absorbent for the separation of organic pollutants from water via hydrophobic and π–π interactions. Due to the advantages of Raman spectroscopy, which provides an intrinsic molecular Raman signal, typical organic pollutants such as benzene, toluene, ethylbenzene, and xylene (BTEX) were identified by a portable Raman spectrometer with a label-free method after separation through the developed sensor. Further, binary and ternary mixtures of BTEX were also recognized by comparing the Raman spectrum of each component in the mixtures and easily classified by principal component analysis (PCA). Finally, absorbent capacity, reusability tests, and application to environmental water using the developed hBN/AgNWs/sponge samples showed the excellent organic pollutant separation properties as a hydrophobic sponge and the cost effective utilization of the developed sensor for molecular detection. The developed hBN/AgNWs/sponge sensor is expected to be applicable for various on-site and label-free separations and identifications of organic substances, such as environmental and biomedical monitoring.

The detection of toxic gas molecules using the surface-enhanced Raman spectroscopy (SERS) technique is very challenging due to the low affinity of gas molecules. Here, we report extremely sensitive SERS-based NO2 gas sensors based on 3D nanoporous Au nanostructures with a high affinity for NO2 gas molecules and high density of hotspots.

Significant changes of macrocyclic aromaticity in expanded porphyrins through C60 complexation were studied by 1H NMR spectroscopy and nucleus-independent chemical shift calculations. This work is a detailed research study of how the formation of a complex of dual aromatic expanded porphyrin with fullerene affects the electron densities in the main conjugation pathways and meso-substituents. Furthermore, we found that the formation of the photoinduced charge-separated state and the triplet excited-state populations of the bowl-shaped and rigid expanded porphyrin can be controlled by a simple complexation with C60.

A novel carbazole-containing porphyrinoid 4H and its oligomers 6H and 7H were synthesized for the first time via the Suzuki–Miyaura cross-coupling reaction. The structures of 4H, 4Pd, 6H, and 6Zn were finally confirmed by X-ray analysis. The exciton coupling strength (628 cm−1) in 4Zn, 6Zn, and 7Zn was found to be larger than that of the directly-linked porphyrin arrays (570 cm−1), extending their absorption spectra to the NIR region as well as enhancing the extinction coefficients.

International audience; Diazachlorin and diazabacteriochlorin have been prepared through reduction of diazaporphyrin and their in vitro and in vivo activity in photodynamic therapy has been investigated.

Developing a sensor that identifies and quantifies trace amounts of analyte molecules is crucially important for widespread applications, especially in the areas of chemical and biological detection. By non-invasively identifying the vibrational signatures of the target molecules, surface-enhanced Raman scattering (SERS) has been widely employed as a tool for molecular detection. Here, we report on the reproducible fabrication of wafer-scale dense SERS arrays and single-nanogap level near-field imaging of these dense arrays under ambient conditions. Plasmonic nanogaps densely populated the spaces among globular Ag nanoparticles with an areal density of 120 particles per μm2 upon application of a nanolithography-free simple process consisting of the Ar plasma treatment of a polyethylene terephthalate substrate and subsequent Ag sputter deposition. The compact nanogaps produced a high SERS enhancement factor of 3.3 × 107 and homogeneous (coefficient of variation of 8.1%) SERS response. The local near fields at these nanogaps were visualized using photo-induced force microscopy that simultaneously enabled near-field excitation and near-field force detection under ambient conditions. A high spatial resolution of 3.1 nm was achieved. Taken together, the generation of a large-area SERS array with dense plasmonic nanogaps and the subsequent single-nanogap level characterization of the local near field have profound implications in the nanoplasmonic imaging and sensing applications.

Nitrogen dioxide (NO2) produced by hydrocarbon combustion has a significant adverse impact on human health and the environment. In the current work, we developed a high-performance (limit of detection: 0.1 ppm), on-site, rapid NO2 gas sensor that could be operated under ambient conditions by combining a highly sensitive 3D porous SERS substrate and a handheld Raman spectrometer.

Exciton transport in meso-tetra(4-sulfonatophenyl) porphyrin (TPPS) J-aggregates was directly imaged using the emission profile analysis method with confocal fluorescence microscopy. By controlling the structural hierarchy of TPPS aggregates, we could comparatively study the exciton transport properties in single nanotubes and bundled structures. Using the one-dimensional diffusion model, the exciton diffusion coefficients of TPPS nanotubes and bundles were estimated as 95 and 393 nm2 ps-1, respectively, showing a dramatic enhancement of exciton transport in bundled structures. To reveal the underlying mechanism of enhanced exciton transport in bundle compared to that in single strands, the spatially resolved measurements of exciton transport images were correlated with the spectral information at each local sites. We have confirmed that nanotube and its bundled form possess different energetic landscapes and exciton migration dynamics. Agglomeration into bundles led to an increase in system-environment coupling and denser distribution of energy states, facilitating longer migration length and accelerated transport. Detailed analysis in this study provides important insights into the structure-dependent exciton transport properties of self-assembled J-aggregate nanostructures.

Excitation transfer from 1BODIPY* to bisstyrylBODIPY followed by electron transfer to C60 leading to a charge separated state of appreciable lifetime in a supramolecularly assembled triad is demonstrated, as a mimic of the photosynthetic ‘antenna-reaction centre’.

π-Conjugated oligothiophene is considered a chain segment of its polymeric counterpart, whose size and shape can be precisely controlled. Because of its simplified structure, it is possible to understand complex excited-state dynamics of the π-conjugated polymers by employing a bottom-up approach. We review theoretical and experimental aspects of π-conjugated oligothiophenes by summarizing recent works employing time-resolved spectroscopy. The extent of exciton delocalization, which is a prerequisite to efficient charge generation at organic heterojunctions, is described sequentially in model linear and cyclic oligothiophenes, and their analogues. The heterogeneous nature of these systems is highlighted by illustrating the results at both ensemble and single-molecule levels. Exciton dynamics that arise in the polymers are also covered and the signifcance of exciton and charge delocalization in photovoltaic materials is highlighted.

Enhancing light–matter interactions is essential to improving nanophotonic and optoelectronic device performance. In the present work, we developed a new design for 3D plasmonic nanostructures with enhanced near-field interactions among the plasmonic nanomaterials. The 3D plasmonic nanostructures consisted of multilayered bottom Ag/polydimethylsiloxane (PDMS) nanostructures, an alumina middle layer, and top Ag nanoparticles (NPs). High areal density PDMS nanoprotrusions were self-organized by a simple maskless plasma etching process. The conformal deposition of alumina using atomic layer deposition and Ag deposition produced 3D plasmonic nanostructures. These structures induced multiple near-field interactions between the ultrahigh-areal-density (1400 μm−2) top Ag NPs and the underlying Ag nanostructures, and among the top Ag NPs themselves. The high density of hot spots across the 3D space yielded highly efficient and widely tunable plasmonic responses across the entire visible range. The SERS signal enhancement measured at the 3D plasmonic nanostructures was 3.9 times the signal measured at the 2D multilayered structures and 48.0 times the signal measured at a Ag NP layer deposited onto a Si substrate. Finally, the 3D plasmonic nanostructures exhibited excellent uniformity with a variation of 6.8%, based on a microscale Raman mapping analysis. The excellent Raman signal uniformity can be attributed to the ultrahigh areal density of the Ag NPs and the uniform thickness of the alumina spacing layer.

Oxidative fusion reactions of meso-phenoxazino Ni(II) porphyrin were found to be temperature dependent, giving rise to either a doubly phenylene-fused product at room temperature or a singly phenoxazine-fused product at 70 °C. The latter was further oxidized to a doubly phenoxazine-fused Ni(II) porphyrin, which was subsequently converted to the corresponding free base porphyrin and Zn(II) porphyrin. Compared to previously reported diphenylamine-fused porphyrins that displayed a molecular twist, doubly phenoxazine-fused porphyrins exhibited distinctly different properties owing to their highly planar structures, such as larger fluorescence quantum yields, formation of an offset face-to-face dimer both in solution and the solid state, and the generation of a mixed-valence π-radical cation dimer upon electrochemical oxidation. One-electron oxidation of the phenoxazine-fused Ni(II) porphyrin with Magic Blue gave the corresponding radical cation, which was certainly stable and could be isolated by separation over a silica gel column but slowly chlorinated at the reactive β-positions in the solid state. This finding led to us to examine β, β′-dichlorinated phenoxazine-fused and diphenylamine-fused Ni(II) porphyrins, which, upon treatment with Magic Blue, provided remarkably stable radical cations to an unprecedented level. It is actually possible to purify these radical cations by silica gel chromatography, and they can be stored for over 6 months without any sign of deterioration. Moreover, they exhibited no degradation even after the CH2Cl2 solution was washed with water. However, subtle structural differences (planar versus partly twisted) led to different crystal packing structures and solid-state magnetic properties.

The photophysical properties of neutral, monocation radical, and dication of dithiadiazuliporphyrin have been examined with a particular focus on their aromaticity. Dithiadiazuliporphyrin exhibits significantly different characteristics depending on its oxidation state. From these features, we could conclude that the aromaticity of dithiadiazuliporphyrin is changed from nonaromatic to aromatic upon oxidation from neutral to monocation radical and dication by Br2.

Herein, we revealed a symmetry-breaking charge transfer (SBCT) process in the excited state of a directly linked push-pull porphyrin dyad (AD) and triad (ADA) via spectroscopic measurements including steady-state absorption and fluorescence, time-resolved fluorescence (TRF), femtosecond transient absorption (fs-TA), and time-resolved infrared (TRIR) measurements. Unprecedented broad fluorescence spectra were observed for porphyrin arrays in polar solvents; these were attributed to the existence of a charge transfer state as evidenced by the TRF measurements. TA measurements also revealed emerging features of a CT state for AD and ADA in polar solvents. These dynamics were also confirmed via TRIR measurements, which provided further information on the solvation and structural relaxation processes of the SBCT process. This is the first observation of an SBCT process in porphyrin arrays, providing fundamental understanding of the strongly coupled porphyrin arrays. Thus, the results of this study reveal the potential of the porphyrin arrays in relevant applications requiring SBCT.

Correction for ‘Changes in macrocyclic aromaticity and formation of a charge-separated state by complexation of expanded porphyrin and C60’ by Won-Young Cha et al., Chem. Commun., 2019, 55, 8301–8304, DOI: 10.1039/C9CC03928G.

Oxidation of 10,15,20-triaryl Ni(II)-porphyrins bearing an electron-withdrawing substituent at the 5-position with DDQ and FeCl3 gave 10,12- and 18,20-doubly phenylene-fused Ni(II)-porphyrins regioselectively. A doubly phenylene-fused meso-chloro porphyrin thus prepared was reductively coupled to give a meso-meso linked dimer, which was further converted to a quadruply phenylene-fused meso-meso, beta-beta, beta-beta triply linked Zn(II)-diporphyrin via inner-metal exchange followed by oxidation with DDQ and Sc(OTf)(3). As compared to the usual meso-meso, beta-beta, beta-beta triply linked Zn(II)-diporphyrin, this pi-extended porphyrin dyad exhibits a smaller HOMO-LUMO gap and a larger two-photon absorption cross-section.

The photophysical properties of molecular arrays are strongly dependent on a variety of structural factors: the constituent chromophores, dihedral angle, linkage length, linkage position, the center-to-center distance between chromophores, and the linker itself. Here, we investigated the exciton coupling dynamics of syn- and anti-type β-β directly linked Zn(ii) porphyrin linear arrays. Focusing on the relationship between the origin of the lowest excited electronic state and the linkage position, we evaluated the exciton coupling strength and carried out time-dependent density functional theory (TDDFT) calculations on model compounds as well as femtosecond transient absorption anisotropy (fs-TAA) measurements. Based on our experiments and calculations, we propose that a different origin of the lowest excited state leads to linkage-position-dependent exciton coupling. In short, compared with syn-type porphyrin arrays, anti-type arrays induce distinct and stronger exciton coupling in the lowest excited state.

Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization efficiencies which are determined by analyses of photoluminescence blinking dynamics. This result suggests that the composition of encapsulated QDs is closely associated with the charge trapping processes, and also provides an insight into the development of more environmentally friendly QD-based devices.

Open-shell singlet diradicaloids have recently received much attention due to their unique optical, electronic and magnetic properties and promising applications in materials science. Among various diradicaloids, quinoidal π-conjugated molecules have become the prevailing design. However, the need for a fundamental understanding on how the fusion mode and pro-aromaticity/anti-aromaticity affect their diradical character and physical properties remains unaddressed. In this work, a series of pro-aromatic benzo-thia-fused [n]thienoacenequinodimethanes (Thn-TIPS (n = 1-3) and BDTh-TIPS) were synthesized and compared with the previously reported anti-aromatic bisindeno-[n]thienoacenes (Sn-TIPS, n = 1-4). The ground-state geometric and electronic structures of these new quinoidal molecules were systematically investigated by X-ray crystallographic analysis, variable temperature NMR, ESR, SQUID, Raman, and electronic absorption spectroscopy, assisted by DFT calculations. It was found that the diradical character index (y0) increased from nearly zero for Th1-TIPS to 2.4% for Th2-TIPS, 18.2% for Th3-TIPS, and 38.2% for BDTh-TIPS, due to the enhanced aromatic stabilization. Consequently, with the extension of molecular size, the one-photon absorption spectra are gradually red-shifted, the two-photon absorption (TPA) cross section values increase, and the singlet excited state lifetimes decrease. By comparison with the corresponding anti-aromatic analogues Sn-TIPS (n = 1-3), the pro-aromatic Thn-TIPS (n = 1-3) exhibit larger diradical character, longer singlet excited state lifetime and larger TPA cross section value. At the same time, they display distinctively different electronic absorption spectra and improved electrochemical amphotericity. Spectroelectrochemical studies revealed a good linear relationship between the optical energy gaps and the molecular length in the neutral, radical cationic and dicationic forms. Our research work discloses a significant difference between the pro-aromatic and anti-aromatic quinoidal compounds and provides guidance for the design of new diradicaloids with desirable properties.

Porphyrin and subphthalocyaninatoboron(iii) chromophores have been fused through a quinoxaline moiety, resulting in the first porphyrin-subphthalocyaninatoboron(iii)-fused hybrid with intramolecular charge transfer from tetrapyrrole/tripyrrole chromophores to the quinoxaline moiety. The unique plane-bowl molecular structure of this hybrid was revealed based on single crystal X-ray diffraction analysis for the first time.

The photophysical properties of a series of highly π-conjugated benzoporphyrin molecules (BPNs) with different shapes were investigated in the condensed phase using single-molecule fluorescence spectroscopy. The fluorescence properties of single BPNs were found to be affected by the number of porphyrin units and their molecular shapes. Notably, the single-molecule fluorescence dynamics of the BPNs revealed an increase in the fluorescence lifetimes and blue shifts of the fluorescence spectra indicative of decreasing π-conjugation pathways in the molecules. The distributions of the spectroscopic parameters and the photostability for the molecules also suggest conformational complexities and heterogeneities. Specifically, as the number of constituent porphyrin units increased, the one-step photobleaching behavior ratio and photostability decreased, and the spectroscopic parameter distributions broadened. The structural properties of the BPNs were also directly determined using defocused wide-field imaging and linear dichroism analyses. In particular, molecules with the same number of constituent porphyrins but different molecular shapes exhibited distinct photophysical properties. In summary, these observations provide guidance for the design of molecular systems that can enhance the performance of molecular electronic devices.

Semi-transparent CH3NH3PbI3 (MAPbI3) planar sandwich solar cells could be fabricated by simply laminating an FTO (F doped tin oxide)/TiO2/MAPbI3/wet hole transporting material (HTM) with additives and PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid))/indium tin oxide (ITO). The best FTO/TiO2/MAPbI3/P3HT with additives/PEDOT:PSS/ITO planar sandwich structured solar cells exhibited a 12.8% (deviation: 11.7% ± 0.74%) average power conversion efficiency (ηavg) but poor visible transmittance due to strong absorption by P3HT. Meanwhile, the semi-transparent FTO/TiO2/MAPbI3/PTAA with additives/PEDOT:PSS/ITO planar sandwich solar cells exhibited a 15.8% (deviation: 14.45% ± 0.76%) ηavg without significant J–V hysteresis with respect to the forward and reverse scan directions. The average visible transmittance (AVT) was controlled from 17.3% to 6.3% and the corresponding ηavg changed from 12.55% to 15.8%. The unsealed sandwich planar perovskite solar cells exhibited great air and humidity stability over 20 days due to the self-passivated device architecture of the sandwich type device.

With the goal of discovering a new and plausible approach to utilizing the conjugated side chains (CSCs), other than for the previously reported purpose of two-dimensional (2D) π-conjugation extension in π-conjugated polymers, we report, for the first time, the impact of with/without interactions induced via resonance in CSCs on the molecular weight (Mw) and photovoltaic performance of polymers. For this, we designed two donor (D)–acceptor (A) polymers, represented as PBDTBPA(H)-DPP and PBDTBPA(F)-DPP, containing alkoxy-BPA(H) and alkoxy-BPA(F) [BPA = biphenylethynyl] on the benzodithiophene (BDT) unit as novel CSCs, respectively. The introduction of these CSCs generated bis-tolane as an integrated part of the BDT unit, which allowed us to address the difference in the polymerization, photophysical, and photovoltaic properties of PBDTBPA(H)-DPP and PBDTBPA(F)-DPP, as a function of the structural variation of CSCs, which has never been investigated in organic solar cells (OSCs). In contrast to the weak electron-donating nature of BPA(H), BPA(F) exhibited a strong electron-donating ability due to the interaction of the lone pair electrons of the fluorine atom with the triple bond via resonance, which decreased the rigidity of the triple bond, whereas in PBDTBPA(H)-DPP the rigidity of the triple bond was retained with no such interaction. The striking differences in the rigidity and different electron-withdrawing tendencies of the CSCs were well correlated with Mw and with the highest occupied molecular orbital (HOMO) energy levels of the polymers. As a result, the inverted OSCs based on PBDTBPA(H)-DPP achieved an open-circuit voltage (Voc) of 0.74 V, and power conversion efficiency (PCE) of 5.58%, which was 38% higher than that of PBDTBPA(F)-DPP-based inverted OSCs. More significantly, the inverted OSC devices were highly stable, retaining 80% of their original PCE after 60-day storage in air, even without encapsulation. To the best of our knowledge, this 5.58% is the highest PCE reported to date for the arylethynyl-substituted BDT donor-based OSCs. These results reveal that bis-tolane [BDTBPA(H)] as an integrated part of the new BDT unit is a promising donor building block for high Mw donor polymers in addition to 2D extended π-conjugation for high performance bulk heterojunction (BHJ) OSCs.

Materials based on biradicals/biradicaloids have potential applications for organic electronics, photonics and spintronics. In this work, we demonstrated that hybridization of porphyrin and polycyclic aromatic hydrocarbon could lead to a new type of stable biradicals/biradicaloids with tunable ground state and physical property. Mono- and bis-phenalenyl fused porphyrins 1 and 2 were synthesized via an intramolecular Friedel–Crafts alkylation-followed-by oxidative dehydrogenation strategy. Our detailed experimental and theoretical studies revealed that 1 has a closed-shell structure with a small biradical character (y = 0.06 by DFT calculation) in the ground state, while 2 exists as a persistent triplet biradical at room temperature under inert atmosphere. Compound 1 underwent hydrogen abstraction from solvent during the crystal growing process while compound 2 was easily oxidized in air to give two dioxo-porphyrin isomers 11a/11b, which can be correlated to their unique biradical character and spin distribution. The physical properties of 1 and 2, their dihydro/tetrahydro-precursors 7/10, and the dioxo-compounds 11a/11b were investigated and compared.

Foldamer systems comprised of two perylene bisimide (PBI) dyes attached to the conjugated backbones of 1,2-bis(phenylethynyl)benzene and phenylethynyl-bis(phenylene)indane, respectively, were synthesized and investigated with regard to their solvent-dependent properties. UV/Vis absorption and steady-state fluorescence spectra show that both foldamers exist predominantly in a folded H-aggregated state consisting of π–π-stacked PBIs in THF and in more random conformations with weaker excitonic coupling between the PBIs in chloroform. Time-resolved fluorescence spectroscopy and transient absorption spectroscopy reveal entirely different relaxation pathways for the photoexcited molecules in the given solvents, i.e. photoinduced electron transfer leading to charge separated states for the open conformations (in chloroform) and relaxation into excimer states with red-shifted emission for the stacked conformations (in THF). Supported by redox data from cyclic voltammetry and Rehm–Weller analysis we could relate the processes occurring in these solution-phase model systems to the elementary processes in organic solar cells. Accordingly, only if relaxation pathways such as excimer formation are strictly avoided in molecular semiconductor materials, excitons may diffuse over larger distances to the heterojunction interface and produce photocurrent via the formation of electron/hole pairs by photoinduced electron transfer.

A new strategy for constructing large Stokes shift dyes by coupling a low quantum yield (less than 1%) BODIPY donor (BDN) with tunable high quantum yield BODIPY acceptors (BDM) has been explored to synthesize a set of novel Dark Resonance Energy Transfer (DRET) dyes, named BNM. The low quantum yield of the donor is ascribed to the intramolecular rotation of the phenyl rings, which has been proven by controlling the viscosity and temperature of the solvent. However, upon excitation of BNM compounds at the donor absorption wavelength, tunable emissions from 560 nm to 617 nm were obtained, with a high quantum yield of up to 0.75. Ultrafast dynamic studies demonstrated that the absorbed energy was transferred to the acceptor (BDM) with a high energy transfer rate, before being quenched by non-radiative intramolecular rotations. Using a dark donor makes it possible to avoid fluorescence leaks from donor emission. This is a new set of RET dyes that can be excited by a low quantum yield donor to emit a tunable wide range of high fluorescence emission.

An o-phenylenevinylene-bridged tetrapyrrolic macrocycle (2) was synthesized by means of a Horner-Wadsworth-Emmons reaction between benzylbisphosphonate and SEM-protected diformylpyrrole, followed by deprotection of the SEM groups. This conformationally flexible tetrapyrrole can be considered as an expanded calix[4]pyrrole analogue, which acts as a receptor for the chloride and bromide anions in THF-d8, but undergoes deprotonation upon exposure to the fluoride anion.

Highly uniform 3D ZnO hollow shell structures were prepared by combining prism holographic lithography (PHL) and atomic layer deposition (ALD). As a dense ZnO film was obtained by using the ALD process, no volume shrinkage occurred during the subsequent calcination to remove the sacrificial polymer template. No volume shrinkage during heat treatment is crucial for achieving excellent optical properties and mechanical stability of inverse photonic crystals (PCs).

Recent studies demonstrated that aromaticity and biradical character play important roles in determining the ground-state structures and physical properties of quinoidal polycyclic hydrocarbons and oligothiophenes, a kind of molecular materials showing promising applications for organic electronics, photonics and spintronics. In this work, we designed and synthesized a new type of hybrid system, the so-called bisindeno-[n]thienoacenes (n = 1–4), by annulation of quinoidal fused α-oligothiophenes with two indene units. The obtained molecules can be regarded as antiaromatic systems containing 4n π electrons with small singlet biradical character (y0). Their ground-state geometry and electronic structures were studied by X-ray crystallographic analysis, NMR, ESR and Raman spectroscopy, assisted by density functional theory calculations. With extension of the chain length, the molecules showed a gradual increase of the singlet biradical character accompanied by decreased antiaromaticity, finally leading to a highly reactive bisindeno[4]thienoacene (S4-TIPS) which has a singlet biradical ground state (y0 = 0.202). Their optical and electronic properties in the neutral and charged states were systematically investigated by one-photon absorption, two-photon absorption, transient absorption spectroscopy, cyclic voltammetry and spectroelectrochemistry, which could be correlated to the chain length dependent antiaromaticity and biradical character. Our detailed studies revealed a clear structure–aromaticity–biradical character–physical properties–reactivity relationship, which is of importance for tailored material design in the future.

Roles of metal nanoparticles (NPs) on graphene-based devices were investigated in terms of gas-sensing characteristics of NO2 and NH3, and flexible gas sensing was also realized for future applications. The synergistic combination of metal NPs and graphene modulates the electronic properties of graphene, leading to enhancement of selectivity and sensitivity in gas-sensing characteristics. Introduction of palladium (Pd) NPs on the graphene accumulates hole carriers of graphene, resulting in the gas sensor being sensitized by NH3 gas molecular adsorption. In contrast, aluminum (Al) NPs deplete hole carriers, which dramatically improves NO2 sensitivity. Furthermore, the sensitivity of flexible graphene-based gas sensors was also enhanced via the same approach, even after 104 bending cycles and was maintained after 3 months.

Polycyclic hydrocarbon with a singlet biradical ground state has recently become a hot topic among various studies on π-conjugated systems and it is of importance to understand the fundamental structure–biradical character–physical properties relationship. In this work, we found that after incorporation of two additional thiophene rings into the closed-shell tetracyano-perylene (Per-CN) and quaterrylenequinodimethanes (QR-CN), the obtained new quinoidal compounds QDTP and QDTQ became a singlet biradical in the ground state due to the recovery of aromaticity of the thiophene rings in the biradical form and additional steric repulsion between the thiophene rings and the rylene unit. The ground state geometries and electronic structures of QDTP and QDTQ were systematically studied by variable-temperature nuclear magnetic resonance, electron spin resonance, superconducting quantum interference device measurements and FT Raman spectroscopy, assisted by density functional theory calculations. Both compounds were found to be a singlet biradical in the ground state with a small singlet–triplet energy gap and the biradical character was enlarged by elongation of the π-conjugation length. Strong one-photon absorption and large two-photon absorption cross-sections were observed for both compounds in the near-infrared region. Our studies demonstrated that a slight structural modification could significantly change the ground state and the electronic, optical and magnetic properties of a pro-aromatic π-conjugated system, and finally lead to new materials with unique properties. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

Photoinduced twisted intramolecular charge transfer (TICT) of meso-(4-dimethylamino)phenylamino subporphyrin 2 and meso-(4-nitro)phenylamino subporphyrin 3 has been revealed by steady-state and time-resolved absorption/fluorescence experiments and quantum calculations. Subporphyrins 2 and 3 undergo molecular twisting at the Cmeso–N bond and the N–Cipso bond, respectively, to trigger intramolecular charge separation, which is restricted at low temperature or in viscous paraffin oil with concurrent fluorescence recovery of local excited states.

A new supramolecular approach to generating a long-lived photoinduced charge separated state is described. It is predicated on the use of tetra-anionic sulfonated porphyrins (1-M4−: M = H2 and Zn) that form 1 : 2 supramolecular complexes with dicationic zinc(II) porphyrinato tetrathiafulvalenes (2-Zn2+) via strong electrostatic interactions. The X-ray crystal structure of the complex 1-Zn4−/(2-Zn2+)2 reveals a slipped sandwich-type interaction wherein 1-Zn4− is covered on both its top and bottom faces by two separate 2-Zn2+ porphyrins. Upon photoexcitation of the supramolecular ensemble, efficient photoinduced electron transfer from 1-M4− to the triplet excited state [2-Zn2+]* occurs to afford the triplet charge-separated (CS) states, as revealed by laser flash photolysis and EPR measurements. The CS state was found to decay via intramolecular back electron transfer within the supramolecular complex. This was evidenced by the observation that the CS state decay of this three-component system obeyed first-order kinetics and afforded the same long lifetimes irrespective of the initial concentrations of the CS state (e.g., 83 ms for the 1-H24−/(2-Zn2+)2 complex in benzonitrile at 298 K). Such an extremely long CS lifetime is thought to result from the spin-forbidden back electron transfer and the small electron coupling term, as inferred from temperature dependent studies of the CS lifetime. Decay of the CS state via intermolecular back electron transfer between two separate CS species of the type [1-M˙3−/(2-Zn˙+)(2-Zn2+)] is not observed, as revealed by the absence of second order decay kinetics. The absence of appreciable bimolecular decay processes and consequently the long-lived nature of the CS state is attributed to the central radical trianionic porphyrin (1-M˙3−) being protected from close-contact interactions with other species, precluding bimolecular decay processes. This supramolecular effect is thought to be the result of the radical species, 1-M˙3−, being sandwiched between two cationic porphyrins (2-Zn˙+ and 2-Zn2+). These latter cationic entities cover the top and bottom of the anionic species thus providing both a physical and electrostatic barrier to intermolecular deactivation processes. These conclusions are supported by solution state binding studies, as well as solid state single crystal X-ray diffraction analyses.

Hierarchically structured mesoporous TiO2 beads (HS-TBs), which are used as photoelectrodes in highly efficient dye-sensitized solar cells (DSCs), were prepared by an electrostatic spray (e-spray) technique. To prepare different sized HS-TBs, the electric field and the concentration of TiO2 particles were carefully controlled, because they are critical factors in preparing size-controlled TiO2 beads. Four different HS-TBs were formulated with average diameters of 250, 450, 700, and 1200 nm as high-quality photoelectrodes for use in DSCs. In this study, we found that the zero-dimensional HS-TBs were the most promising photoelectrode for DSCs due to enhanced charge collection efficiency and better penetration of electrolytes through relatively large pores among the HS-TBs. The HS-TBs were characterized by intensity modulated photocurrent spectroscopy (IMPS), the scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method, Barrett–Joyner–Halenda (BJH) method, and electrochemical analysis. The conversion efficiency of HS-TB photoelectrodes improved with increasing bead size due to the enhanced electron transport through electrodes. The present HS-TB cells exhibit a noticeable improvement in the overall efficiency: maximum 9.54% (1200 nm) versus 5.83% for the reference cell made of a TiO2 nanocrystalline film.

Anatase amphiphilic TiO2 (am-TiO2) nanoparticles with an average diameter of ∼15 nm were synthesized using a sol–gel hydrothermal synthesis. The colloidal dispersion of am-TiO2 in alcoholic solvents had outstanding stability for several months at room temperature (RT). Hierarchically structured TiO2 nanospheres (TiO2-NSs) were then successfully prepared by an electrostatic spray (e-spray) method using the am-TiO2 dispersion at RT. The e-sprayed TiO2-NSs were employed as photoelectrodes for solid-state dye-sensitized solar cells (ss-DSSCs), in which a novel plastic crystal/polymer blend based solid-state electrolyte (PC-SSE), iodine-doped succinonitrile/polyacrylonitrile, was used. A photovoltaic power conversion efficiency (PCE) of ∼7.6% was reached under simulated AM 1.5 G (100 mW cm−2) illumination, while the incident photon-to-electrical current conversion was >60% upon excitation at 550 nm. The unique morphology of the TiO2-NSs, in which primary anatase TiO2 nanoparticles are interconnected within the submicron-scale spheres, exhibited superior characteristics as photoelectrodes for our ss-DSSCs compared to conventional TiO2 nanoparticles (TiO2-NPs). The nanoparticles-in-sphere shape offered enhanced surface area and pore volume for high dye-loading and beneficial solid-state electrolyte (SSE) infiltration, while the submicron-scale of the spheres induced efficient visible-light scattering. The efficient interconnection among the primary anatase TiO2 nanoparticles within the e-sprayed NSs offered enhanced charge collection efficiency and photoelectron density, which were confirmed by intensity-modulated photocurrent/photovoltage spectroscopy and electrochemical impedance spectroscopy. These superior properties of the TiO2-NSs were manifested in the cell performance. The PCE of the TiO2-NS-based ss-DSSCs was >2 times higher than that of TiO2-NP-based ss-DSSCs, with notable concurrent improvement in the short-circuit current (JSC = 13.9 mA cm−2), open circuit voltage (VOC = 765 mV), and fill factor (FF = 71.6%). The optimized cell efficiency of 7.6% is thus far the highest reported efficiency for PC-SSE-based DSSCs. Both the single-crystal-like anatase primary particles and the advantageous morphology effectively contributed to the high performance of the ss-DSSCs. Since the e-spray method is a high-throughput, scalable process, our hierarchically structured TiO2-NSs are a promising material for high-efficiency ss-DSSCs, possessing a range of advantages over conventional TiO2-NPs.

Whilst the excitonic properties of J-aggregates have been investigated in great detail, those of H-aggregates have not been systematically investigated yet. In this regard, we have explored the exciton dynamics and excited-species formation processes in columnar H-aggregates of planar PBI dyes that are stacked in a helical fashion by various spectroscopic techniques such as time correlated single-photon counting and femtosecond pump–probe measurements with anisotropy changes. The outcome of this study is that photogenerated excitons in helically stacked PBI dyes experience complicated relaxation processes that involve excited-state interactions such as exciton delocalization and excimer formation. To scrutinize the exciton dynamics in the helically stacked aggregates, we have also included distorted bay-substituted PBI dyes as reference molecules that exhibit either no or only relatively small-sized dimeric aggregate structures. The comparative study revealed that the excited-state interactions in the large-sized helically stacked aggregates extend beyond two PBI units, leading to a final excimer (here, excimer means not only an “excited dimer” but an “excited multimer”) trap state within ∼50 ps. Although in competition with this relaxation path into the excimeric trap state, exciton diffusion has been revealed by exciton–exciton annihilation processes, occurring at high excitation power. Whilst the excimer formation process interrupts the direct observation of exciton diffusion in these columnar PBI aggregates, the exciton migration distance could be estimated by the incorporation of non-fluorescent PBI quencher molecules. From this analysis we can conclude that the exciton diffusion can reach a length of about 10 monomer units. Although this value appears to be shorter than those values observed for J-aggregates, this result shows that columnar PBI stacks might still be useful for optoelectronic applications if the relaxation process leading to excimer traps is prevented, e.g. by structural modifications of the molecules.

During the last decade, molecular photonics has been highlighted in the field of materials chemistry, providing the possibility of the construction of photonic devices at individual molecular level. In parallel, well-established single molecule fluorescence spectroscopy enables us to assess the functionality of individual devices in the solid state, as such, to propose a better design for actual utilization. In this Highlight, we discuss our single molecule investigations on the excitation energy transfer processes and the conformational dynamics occurring in various porphyrin arrays with a particular focus on the applicability as photonic materials. For the fabrication of molecular photonic devices in the solid state, the maintenance of structural rigidity is of utmost importance to achieve efficient signal transmission.

Porphyrins, which consist of four pyrrolic subunits, are a ubiquitous class of naturally occurring compound with versatile photophysical properties. As an extension of the basic structure of the porphyrin macrocycle, there have been a multitude of approaches to synthesize expanded porphyrins with more than four pyrrole rings, leading to the modification of the macrocyclic ring size, planarity, number of pi-electrons and aromaticity. However, the relationship between the photophysical properties and the structures of expanded porphyrins has not been systematically investigated. The main purpose of this article is to describe the structure-property relationships of a variety of expanded porphyrins based on experimental and theoretical results, which include steady-state and time-resolved spectroscopic characterizations, non-linear absorption ability and nucleus-independent chemical shift calculations.

In a series of thiaaceneporphyrinoids, their conformers exhibit macrocyclic π-conjugation pathways controlled by a dihedral angle between the porphyrin framework and acene planes. Conformational equilibria significantly affect the photophysical properties of these macrocycles.

The role of thiophene bridges in determining the photophysical properties of bridged core-modified hexaphyrins is investigated. Depending on the substituted chalcogen atoms and conjugational perturbation across the thiophene bridges, the bridged core-modified hexaphyrins reveal unique photophysical properties.

Two meso–meso vinylene-bridged Zn(II) porphyrin dimers 1 and 2 were analyzed in terms of the control of their conformational dynamics induced by the rotation around the double bond bridge. The dihedral angles between the two porphyrin rings were modulated through coordination with α,ω-diaminoalkanes of varying chain lengths.