High-Performance Near-Infrared Chlorinated Rylenecarboximide Fluorophores via Consecutive C-N and C-C Bond Formation.

A new class of near-infrared (NIR) fluorophores, PAI, is obtained by consecutive C-N/C-C bond formation between diphenylamines and 9,10-dibromoperylenecarboximide. Owing to the rigid structure, extended π-conjugation and pronounced push-pull substitution, these fluorophores show emission maxima up to 804 nm and large Stokes shifts. The extraordinarily high fluorescence quantum yields from 47 % to 70 % are attributed to chloro substitution in the bay positions of the perylene core. These characteristics, together with high photostability, qualify them as useful NIR emitters for applications as biomarkers and security inks.

Charge Transfer, Intersystem Crossing, and Electron Spin Dynamics in a Compact Perylenemonoimide-Phenoxazine Electron Donor-Acceptor Dyad.

With phenoxazine (PXZ) as the electron donor and perylene-3,4-dicarboximide (PMI) as the electron acceptor, we prepared a compact, orthogonal electron donor-acceptor dyad (PMI-PXZ) to study the spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC). A weak charge transfer (CT) absorption band, due to S0 → 1CT transition, was observed (ε = 2840 M-1 cm-1 at 554 nm, FWHM: 2850 cm-1), which is different from that of the previously reported analogue dyad with phenothiazine as the electron donor (PMI-PTZ), for which no CT absorption band was observed. A long-lived triplet state was observed (lifetime τT = 182 µs) with nanosecond transient absorption spectroscopy, and the singlet oxygen quantum yield (ΦΔ = 76%) is higher than that of the previously reported analogue dyad PMI-PTZ (ΦΔ = 57%). Ultrafast charge separation (ca. 0.14 ps) and slow charge recombination (1.4 ns) were observed with femtosecond transient absorption spectroscopy. With time-resolved electron paramagnetic resonance spectroscopy (TREPR), we confirmed the SOCT-ISC mechanism, and the electron spin polarization phase pattern of the triplet-state TREPR spectrum is (e, e, a, e, a, a), which is dramatically different from that of PMI-PTZ (a, e, a, e, a, e), indicating that the triplet-state TREPR spectrum of a specific chromophore in the electron donor-acceptor dyads is not only dependent on the geometry of the dyads but also dependent on the structure of the electron donor (or acceptor). Even one-atom variation in the donor structure may cause significant influence on the electron spin selectivity of the ISC of the electron donor-acceptor dyads.

A high-efficiency ammonia-responsive solar evaporator.

The use of solar evaporators, which are capable of purifying water through solar energy, is a potentially attractive solution to relieve the world-wide water shortage problem. However, there may be toxic and volatile substances, such as ammonia, in water bodies, which could be evaporated along with water during the evaporation process, causing contamination of the purified water. In this work, we report an efficient ammonia responsive high-efficiency solar evaporator based on the titanium dioxide nanoparticle (TiO2NP) and polypyrrole nanoparticle (PPyNP) composite. Owing to the synergistic effect between the photo-induced hydrophilicity of the TiO2NPs and the photothermal effect of the PPyNPs, the solar evaporator is able to transport and evaporate water with an efficiency as high as 97.3% and an evaporation rate of 2.9 kg m-2 h-1 (under 2 sun irradiation). Interestingly, due to the ammonia responsiveness, the solar evaporator acts smartly and stops working in the presence of ammonia, thus avoiding the evaporation of this contaminant. In addition, the current solar evaporator is capable of degrading organic pollutants (e.g. dyes), which relies on the photocatalytic activity of TiO2NPs. We thus believe that the ammonia responsive solar evaporator reported in the current study may have great potential in the practical field.

Charge separation, recombination and intersystem crossing of directly connected perylenemonoimide-carbazole electron donor/acceptor dyads.

Perylenemonoimide (PMI)-carbazole (Cz) compact electron donor/acceptor dyads were prepared to study the relationship between the mutual orientation of the electron donor/acceptor in the dyads and the spin-orbit charge transfer intersystem crossing (SOCT-ISC) efficiency. The PMI and the Cz units are connected via either a C-C or C-N bond, or with an intervening phenyl moiety. The photophysical properties of the dyads were studied with steady state and time-resolved optical spectroscopies. The fluorescence of the PMI unit in the dyads was generally quenched, due to photo-induced electron transfer, especially in polar solvents (the fluorescence has a biexponential decay in acetonitrile, τF = 1.4 ns/population ratio: 98.9%, and 9.6 ns/population ratio: 1.1%). The triplet state (lifetime τT = 14.7 µs) formation of the dyads is dependent on the solvent polarity, which is characteristic for SOCT-ISC. Femtosecond transient absorption spectra show that the charge separation takes 0.28 ps and the charge recombination takes 1.21 ns. Reversible photo-reduction of the PMI-Cz dyads and generation of the near IR-absorbing (centered at 604 nm and 774 nm) PMI radical anion (PMI-˙) were observed in the presence of a sacrificial electron donor (triethylamine). These results are useful for study of the fundamental photochemistry of compact electron donor/acceptor dyads and for design of new heavy atom-free triplet photosensitizers.

Low-Cost, Robust Pressure-Responsive Smart Windows with Dynamic Switchable Transmittance.

Mechanically responsive smart windows with adjustable light transmittance have attracted more and more attention due to their great potential in our daily life. However, their fabrication normally requires complicated preparation such as oxygen plasma treatment and high-cost materials (i.e., poly(dimethylsiloxane) (PDMS)), which hinders their practical applications. Herein, a principally different mechanically responsive smart window, i.e., a pressure-responsive smart window, is reported, which is achieved by harnessing the synergistic interactions (i.e., hydrogen bonding and surface roughness compensation) between the two constituent parts, i.e., hydrogel and agar films. The pressure-responsive smart window features the ultrafast response time (37.5 ms) and high transmittance changes (∼50%) with excellent repeatability, which can be stained with different colors and operated on a flexible substrate. Since the pressure-responsive smart window enables the utilization of the low-cost material and does not require the external energy input, it is anticipated that it may have great potential in practical applications.

Visible-Light-Driven Water-Fueled Ecofriendly Micromotors Based on Iron Phthalocyanine for Highly Efficient Organic Pollutant Degradation.

The light-driven micromotor has been demonstrated to have great potential in the environmental remediation field. However, it is still challenging to develop highly efficient, ecofriendly, and visible-light-powered micromotors for organic pollutant degradation. In this paper, we report an ecofriendly micromotor based on iron phthalocyanine (FePc) and gelatin, which exhibits the visible-light-driven self-propulsion behavior using water fuel based on the photocatalytic reaction and self-diffusiophoresis mechanism. Fast motion behavior is observed which induces the rapid agitation of the solution. This, together with the excellent photocatalytic activity, makes the FePc-based micromotor highly efficient when utilized in the degradation of organic pollutants with a normalized reaction rate constant of 2.49 × 10-2 L m-2 s-1, which is by far the fastest and is far superior than the stationary counterpart. The external fuel-free propulsion and the high efficiency in pollutant degradation make the current micromotor potentially attractive for environmental remediation.

Calligraphy/Painting Based on a Bioinspired Light-Driven Micromotor with Concentration-Dependent Motion Direction Reversal and Dynamic Swarming Behavior.

Inspired by the collective behavior of natural living systems, the collective behavior of micromotors has become the research highlight. Although great progress has been made, it is still challenging to control the collective behavior of micromotors. In this paper, we demonstrate a novel near-infrared (NIR) light-powered micromotor consisting of a polystyrene microsphere and a polydopamine core-shell structure (PS@PDA) with concentration-dependent motion direction reversal and dynamic swarming behavior. Among others, a single micromotor exhibits negative phototaxis, whereas a group of micromotors shows positive phototaxis, which can be attributed to the competition between the thermophoretic force and hydrodynamic drag caused by the thermal buoyancy. In addition, because of the reversible hydrogen bonding and π-π stacking interactions between the adjacent PS@PDA micromotors, they form aggregation as a result of the positive phototaxis with dynamically controllable shapes tuned by the irradiation position, which makes them potentially attractive for in-solution calligraphy and painting. It is anticipated that the current study may not only provide a new strategy to control the collective behavior of the micromotors, but also promote their application in the practical field.

One-Step Fabrication of Dual Optically/Magnetically Modulated Walnut-like Micromotor.

In this paper, we report a novel multi-responsive walnut-like micromotor consisting of polycaprolactone (PCL), iron oxide nanoparticles (Fe3O4 NPs), and catalase, which is constructed through a one-step electrospinning method. Based on the catalytic activity and photothermal and magnetic responsiveness originating from catalase and Fe3O4 NPs, respectively, the resulting micromotor exhibits an autonomous movement in the presence of hydrogen peroxide (H2O2) fuel, controlled motion velocity under light irradiation, and guided movement direction upon the application of an external magnetic field. Owing to the hydrophobic nature of the PCL polymer constituent inside the micromotor, the autonomous moving micromotor can collect spilled oil inside a solution once it collides with the oil droplet. Since the micromotor could be separated out using a magnetic field, we believe the current walnut-like micromotor holds great promise in the field of environmental remediation.

Spin-orbit charge transfer intersystem crossing in perylenemonoimide-phenothiazine compact electron donor-acceptor dyads.

The spin-orbit charge transfer intersystem crossing (SOCT-ISC) of perylenemonoimide-phenothiazine compact dyads was shown to depend on the molecular geometry and the vector dipole orientations of the two chromophores, and the dyads show high triplet state quantum yields (57%).

Surface-Assisted Alkane Polymerization: Investigation on Structure-Reactivity Relationship.

Surface-assisted polymerization of alkanes is a remarkable reaction for which the surface reconstruction of Au(110) is crucial. The surface of (1×2)-Au(110) precovered with molecules can be completely transformed into (1×3)-Au(110) by introducing branched methylidene groups on both sides of the aliphatic chain (18, 19-dimethylidenehexatriacontane) or locally shifted into (1×3)-Au(110) under exposure to low-energy electrons (beam energy from 3.5 to 33.6 eV, for alkane dotriacontane). Scanning tunneling microscopy investigations demonstrate that alkane chains adsorbed on (1×3)-Au(110) are more reactive than on (1×2)-Au(110), presenting a solid experimental proof for structure-reactivity relationships. This difference can be ascribed to the existence of an extra row of gold atoms in the groove of (1×3)-Au(110), providing active sites of Au atoms with lower coordination number. The experimental results are further confirmed by density functional theory simulations.

Effect of fluorination of naphthalene diimide-benzothiadiazole copolymers on ambipolar behavior in field-effect transistors.

Two naphthalene diimide (NDI)-benzothiadiazole (BT) based conjugated polymers with high molecular weight, P1 and P2, were synthesized by introducing F atoms to modulate the electron-donating ability of the BT moiety. 3-Decyl-pentadecyl branched alkyl side chains were employed and expected to improve the molecular organization and device performance. Both polymers have excellent solubility in common organic solvents. UV-vis-NIR absorption and cyclic voltammetry indicate that the maximum absorption wavelength of P2 is blue-shifted and the HOMO energy level of P2 is decreased in comparison with P1. Two dimensional wide angle X-ray scattering of thin films revealed a similar organization of both polymers. A less balanced transport in field-effect transistors with increased electron mobility of 0.258 cm2 V-1 s-1 and lowered hole transport of 2.4 × 10-3 cm2 V-1 s-1 was found for P2. Polymer devices of P1 exhibited a balanced ambipolar transport, with a hole mobility of 0.073 cm2 V-1 s-1 and electron mobility of 0.086 cm2 V-1 s-1.

Two-Dimensional Chirality Transfer via On-Surface Reaction.

Two-dimensional chirality transfer from self-assembled (SA) molecules to covalently bonded products was achieved via on-surface synthesis on Au(111) substrates by choosing 1,4-dibromo-2,5-didodecylbenzene (12DB) and 1,4-dibromo-2,5-ditridecylbenzene (13DB) as designed precursors. Scanning tunneling microscopy investigations reveal that their aryl-aryl coupling reaction occurs by connecting the nearest neighboring precursors and thus preserving the SA lamellar structure. The SA structures of 12(13)DB precursors determine the final structures of produced oligo-p-phenylenes (OPP) on the surface. Pure homochiral domains (12DB) give rise to homochiral domains of OPP, whereas lamellae containing mixed chiral geometry of the precursor (13DB) results in the formation of racemic lamellae of OPP.

The Importance of End Groups for Solution-Processed Small-Molecule Bulk-Heterojunction Photovoltaic Cells.

End groups in small-molecule photovoltaic materials are important owing to their strong influence on molecular stability, solubility, energy levels, and aggregation behaviors. In this work, a series of donor-acceptor pentads (D2 -A-D1 -A-D2 ) were designed and synthesized, aiming to investigate the effect of the end groups on the materials properties and photovoltaic device performance. These molecules share identical central A-D1 -A triads (with benzodithiophene as D1 and 6-carbonyl-thieno[3,4-b]thiophene as A), but with various D2 end groups composed of alkyl-substituted thiophene (T), thieno[3,2-b]thiophene (TT), and 2,2'-bithiophene (BT). The results indicate a relationship between conjugated segment/alkyl chain length of the end groups and the photovoltaic performance, which contributes to the evolving molecular design principles for high efficiency organic solar cells.