The impact of molecular orientations on the energy levels of A-D-A acceptors: implications for the charge separation driving force of organic solar cells.

The energetic landscape of charge carriers, namely the ionization potential (IP) and electron affinity (EA), can play a crucial role in the charge separation and migration processes for organic solar cells (OSCs). However, the impact of molecular orientations on the energy levels remains elusive, especially in acceptor-donor-acceptor (A-D-A) type nonfullerene acceptors (NFAs) with intrinsic anisotropy. Using the self-consistent quantum mechanics/embedded charge (sc-QM/EC) approach, we have investigated the energy level shifts from the edge-on or face-on surfaces to the bulk phase for three typical NFA crystals, IDIC-4F, INIC-4F, and Y6. The results point out that the surface-to-bulk changes in IP are limited within 0.2 eV for both the orientations due to the mutual counteraction between the electrostatic and induction effects. In sharp contrast, the EA values are substantially decreased from the bulk to the surfaces; especially, for the face-on orientation, the reduction reaches 0.5-0.8 eV. This indicates that the face-on orientation can provide a significant driving force for electrons moving from the surface or the interface to the bulk phase and thus improve the charge separation efficiency. Our work indicates that enhancing the face-on orientation is an effective method to increase the charge separation driving force for the OSCs based on A-D-A NFAs.

The Key Descriptors for Predicting the Exciton Binding Energy of Organic Photovoltaic Materials.

Exciton binding energy (Eb) is a key parameter to determine the mechanism and performance of organic optoelectronic devices. Small Eb benefits to reduce the interfacial energy offset and the energy loss of organic solar cells. However, quantum-chemical calculations of the Eb in solid state with considering electronic polarization effects are extremely time-consuming. Furthermore, current studies lack critical descriptors. Here, we use data-driven machine learning (ML) to accelerate the computation and identify the key descriptors most relevant to the solid-state Eb. The results verify two key descriptors associated with molecular and aggregation-state properties for efficient prediction of the solid-state Eb. Moreover, a very high accuracy is achieved by using the extreme gradient boosting algorithm, with the Pearson's correlation coefficient of 0.92. Finally, we use this ML model to predict the Eb of thin films, which is difficult to achieve using the current quantum-chemical calculations due to the large structural disorder. Remarkably, the predicted thin-film Eb values are fully consistent with the results of temperature-dependent photoluminescence spectra. Therefore, our work provides an accurate and efficient approach to predict the solid-state Eb and would be helpful to accelerate the exploitation of novel promising organic photovoltaic materials.

Tetraphenylporphyrin-based Chelating Ligand Additive as a Molecular Sieving Interfacial Barrier toward Durable Aqueous Zinc Metal Batteries.

The sustained water consumption and uncontrollable dendrite growth strongly hamper the practical applications of rechargeable zinc (Zn) metal batteries (ZMBs). Herein, for the first time, we demonstrate that trace amount of chelate ligand additive can serve as a "molecular sieve-like" interfacial barrier and achieve highly efficient Zn plating/stripping. As verified by theoretical modeling and experimental investigations, the benzenesulfonic acid groups on the additive molecular not only facilitates its water solubility and selective adsorption on the Zn anode, but also effectively accelerates the de-solvation kinetics of Zn2+ . Meanwhile, the central porphyrin ring on the chelate ligand effectively expels free water molecules from Zn2+ via chemical binding against hydrogen evolution, and reversibly releases the captured Zn2+ to endow a dendrite-free Zn deposition. By virtue of this non-consumable additive, high average Zn plating/stripping efficiency of 99.7 % over 2100 cycles together with extended lifespan and suppressed water decomposition in the Zn||MnO2 full battery were achieved, thus opening a new avenue for developing highly durable ZMBs.

Triplet Acceptors with a D-A Structure and Twisted Conformation for Efficient Organic Solar Cells.

Triplet acceptors have been developed to construct high-performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T1 ) are close to those of charge-transfer states (3 CT). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large π-conjugated core and D-A structure, were confirmed to be triplet materials, leading to high-performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D-A structures result in large spin-orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T1 is close to 3 CT, facilitating the split of triplet exciton to free charges.

Dicyclohepta[ijkl,uvwx]rubicene with Two Pentagons and Two Heptagons as a Stable and Planar Non-benzenoid Nanographene.

Polycyclic aromatic hydrocarbons with hexagons/pentagons or hexagons/heptagons have been intensively investigated in recent years, but those with simultaneous presence of hexagons, pentagons and heptagons remain rare. In this paper, we report dicyclohepta[ijkl,uvwx]rubicene (DHR), a non-benzenoid isomer of dibenzo[bc,kl]coronene with two pentagons and two heptagons. We developed an efficient and scalable synthetic method for DHR by using Scholl reaction and dehydrogenation. Crystal structure of DHR shows that the benzenoid rings, two pentagons and two heptagons are coplanar. The bond lengths analysis and the ICSS(1)zz and LOL-π calculations indicate that the incorporation of two formal azulene moieties has an effect on the conjugated structure. The π-electrons of benzenoid and pentagon rings are more delocalized. Cyclic voltammetry studies indicate that DHR shows multiple oxidation and reduction potentials. Interestingly, DHR exhibits unusual S0 to S2 absorption and abnormal anti-Kasha S2 to S0 emission. Moreover, crystals of DHR exhibit semiconducting behaviour with hole mobility up to 0.082 cm2 V-1 s-1 .

High-Performance Ambipolar and n-Type Emissive Semiconductors Based on Perfluorophenyl-Substituted Perylene and Anthracene.

Emissive organic semiconductors are highly demanding for organic light-emitting transistors (OLETs) and electrically pumped organic lasers (EPOLs). However, it remains a great challenge to obtain organic semiconductors with high carrier mobility and high photoluminescence quantum yield simultaneously. Here, a new design strategy is reported for highly emissive ambipolar and even n-type semiconductors by introducing perfluorophenyl groups into polycyclic aromatic hydrocarbons such as perylene and anthracene. The results reveal that 3,9-diperfluorophenyl perylene (5FDPP) exhibits the ambipolar semiconducting property with hole and electron mobilities up to 0.12 and 1.89 cm2 V-1 s-1 , and a photoluminescence quantum yield of 55%. One of the crystal forms of 5FDPA exhibits blue emission with an emission quantum yield of 52% and simultaneously shows the n-type semiconducting property with an electron mobility up to 2.65 cm2 V-1 s-1 , which is the highest value among the reported organic emissive n-type semiconductors. Furthermore, crystals of 5FDPP are utilized to fabricate OLETs by using Ag as source-drain electrodes. The electroluminescence is detected in the transporting channels with an external quantum efficiency (EQE) of up to 2.2%, and the current density is up to 145 kA cm-2 , which are among the highest values for single-component OLETs with symmetric electrodes.

Ladder Oxygenation of Group VIII Metal Clusters and the Formation of Metalloxocubes M13O8.

The diversity of valence and bonding of transition metals makes their oxidation processes perplexing at reduced sizes. Here we report a comprehensive study on the oxidation reactions of rhodium clusters Rhn± (n = 3-30) and find that Rh3,4O4+, Rh5-7O6+, and Rh8-13O8+ always dominate the mass distributions showing size-dependent ladder oxygenation which is closely associated with the O-binding modes. While the Rh8-13O8+ clusters display a µ3-O binding mode (hollow site adsorption), Rh3-4O4+ and Rh5-7O6+ favor the µ2-O binding mode (edge-site adsorption) or a mixture of the two modes. The µ3-O binding mode is inclined to yield a cubic Rh13O8, while the µ2-O binding mode gives rise to oxygen-bridge protection for the metal clusters. Such ladder oxidation was also observed for Ptn+, Fen+, Con+, and Nin+ clusters. We propose a three-dimensional diagram for the oxidation states and O-binding modes of metals, and highlight the metalloxocubes M13O8+ for cluster-genetic materials.

Toward Quantifying the Relation between Exciton Binding Energies and Molecular Packing.

Reducing the exciton binding energy Eb of organic photoactive materials is critical to minimize the energy loss and improve the photovoltaic efficiency of organic solar cells. However, the relation between the Eb and molecular packing is not well understood. Herein, the Eb in the crystals of a series of A-D-A type nonfullerene acceptors with different lengths of alkyl side chains has been examined by self-consistent quantum mechanics/embedded charge calculations. The variation of molecular packing induced by the different alkyl chains can have an important impact on the polarization effect of charge carriers and thereby the Eb. More interestingly, the Eb values are found to be linearly increased with the ratio of the void fraction vs the packing coefficient of molecular backbones in the solid crystals. Owing to the smallest ratio, a remarkable low Eb of several tens of meV is achieved for the acceptor with an optimal length of alkyl chains.

A novel lipid droplets-targeting ratiometric fluorescence probe for hypochlorous acid in living cells.

Lipid droplets were found to be involved in many organism activities. Here, a lipid droplets-targeted near-infrared fluorescence probe (named XHZ) for ratiometric detection of endogenous hypochlorous acid/hypochlorite (HClO/ClO-) in living cells was developed, which was constructed by a coumarin moiety and a malononitrile derivative. XHZ could detect HClO/ClO- with high selectivity and sensitivity in a ratiometric manner based on FRET (Förster Resonance Energy Transfer) mechanism. The two well-resolved emission (470/672 nm) bands could ensure accurate detection of HClO/ClO- in vitro as well as in vivo. XHZ was successfully used for ratiometric fluorescence imaging of exogenous and endogenous HClO/ClO- in RAW264.7 cells. A good linear relationship between the fluorescence intensity ratios of the two emissions and HClO/ClO- concentrations from 0 to 40 µM was obtained. Importantly, XHZ could localize mainly in lipid droplets of RAW264.7 cells. To the best of our knowledge, XHZ is the first lipid droplets-targeted ratiometric fluorescence probe for HClO/ClO-.

A mitochondria-targeted fluorescence probe for ratiometric detection of endogenous hypochlorite in the living cells.

A mitochondria-targeted fluorescence probe (CPBT) for ratiometric detection of endogenous hypochlorite in the living cells was developed. CPBT could detect hypochlorite with high selectivity and sensitivity in a ratiometric manner based on FRET mechanism. In absence of hypochlorite, when CPBT was excited with absorption maximum wavelength of the donor moiety, it showed the emission of acceptor moiety because of FRET process. However, in the presence of hypochlorite, the reaction of CC double bond with hypochlorite interrupted the conjugation system resulting in the inhibition of FRET process and the emission of the donor moiety. The two well-resolved emission bands can ensure accurate detection of hypochlorite. A good linear relationship between the fluorescence intensity ratios of the two emissions and the ClO- concentrations in the range from 41.8 nM (detection limit) to 12.5 µM was established. Importantly, CPBT could localize mainly in the mitochondria of RAW264.7 cells. CPBT was successfully used to fluorescence ratiometric imaging of endogenous hypochlorite in RAW264.7 cells.