Solvent-Assisted Self-Assembly of Fullerene into Single-Crystal Ultrathin Microribbons as Highly Sensitive UV–Visible Photodetectors

The size, shape, and crystallinity of organic nanostructures play an important role in their physical properties and are mainly determined by the self-assembling kinetics of molecular components often involving the solvent conditions. Here, we reported a kinetically controlled self-assembly of C₆₀ assisted by the solvent carbon bisulfide (CS₂) into single-crystal ultrathin microribbons of 2C₆₀·3CS₂, upon mixing the poor solvent isopropyl alcohol with a C₆₀/CS₂ stock solution. Surface energy calculations reveal that these microribbons represent a kinetically favored high-energy state as compared with the thermodynamically stable shape of prismatic rods. High-resolution transmission electron microscopy observations clarify that association of CS₂ at the nucleation stage helps to guide and rigidify the formation of π–π stacking 1D chains of C₆₀ through the surrounding CS₂ cage-like structures, which further act as glue, boosting lateral assembly of as-formed 1D chains into untrathin 2D microribbon single crystals. Precise control over the thickness, width, and length of 2C₆₀·3CS₂ microribbons was achieved by manipulation of the growth kinetics through adjusting the solvent conditions. Upon heating to 120 °C, sublimation of CS₂ components results in fcc C₆₀ microribbons. We found that both microribbons of solvated monoclinic 2C₆₀·3CS₂ and pure fcc C₆₀ exhibit highly sensitive photoconductivity properties with a spectral response range covering UV to visible. The highest on/off ratio of two-terminal photodetectors based on single ribbons reaches around 250, while the responsitivity is about 75.3 A W^–1 in the UV region and 90.4 A W^–1 in the visible region

Compact-Type Quasi-2D Perovskite Based on Two Conventional 3D Perovskites

Quasi-2D perovskites are natural quantum well (QW) structures composed of insulating organic layers inserted between conducting [An–1PbnX3n+1]2– slabs. The presence of the bulky organic layer improves the stability but meanwhile sacrifices carrier transport performance. By utilizing two A-site cations of formamidinium (FA+) and cesium (Cs+), we synthesize unique compact-type quasi-2D perovskites CsPbBr3@FABr. Instead of the bulky organic cations, the FA+ cation was employed to work as interlayer “spacer”, while the smaller Cs+ cation was chosen to occupy perovskite cages. Transient absorption reveals an energy transfer from small-n-value QWs to large-n-value QWs, enabling a photoluminescence quantum yield (PLQY) of 36.1%. After further promoting the formation of middle-n-value QWs, the homogeneous QW distribution provides a complete energy cascade to access more efficient energy transfer, leading to significant PLQY raise to 70.1%. We break the shackles to report the first case of compact-type quasi-2D perovskites, providing new guidelines for designing high-performance perovskite materials for optoelectronic devices

Orange−Blue−Orange Triblock One-Dimensional Heterostructures of Organic Microrods for White-Light Emission

Orange−Blue−Orange Triblock One-Dimensional Heterostructures of Organic Microrods for White-Light Emissio

Controlled Self-Assembly of Organic Microcrystals for Laser Applications

The small organic molecule <i>p</i>-distyrylbenzene (DSB) has been controllably prepared into one-dimensional microwires (1D-MWs) and 2D rhombic microdisks (2D-RMDs) by modulating the growth kinetics in the process of morphology growth. These as-prepared organic microcrystals, 1D-MWs and 2D-RMDs, exhibit a shape-dependent microcavity effect in that the single 1D-MW can act as a Fabry-Pérot (FP) mode lasing resonator while the individual 2D-RMD functions as the whispering-gallery-mode (WGM) microcavity. Moreover, as compared with the 1D FP resonators, there exists a higher quality factor (<i>Q</i>) in the WGM lasing resonator under the identical optical path length. Significantly, the lasing threshold, <i>E</i>_th = 1.02 μJ/cm², of 2D-RMDs is much lower than <i>E</i>_th = 2.57 μJ/cm² of 1D-MWs. Our demonstration can give the direction for the development of the organic solid-state microlasers

Engineering of Interfacial Electron Transfer from Donor–Acceptor Type Organic Semiconductor to ZnO Nanorod for Visible-Light Detection

Interfacial electron transfer (IET) plays a key role in photoactive organic/inorganic hybrid nanomaterials and remains elusive with regard to interfacial energy level alignment. In this study, we prepared hybrid ZnO nanorods by grafting n-type perylene bisimide (PBI) derivatives bearing carboxylic acid groups at nitrogen positions. No evidence in terms of direct electron transfer from PBI to ZnO can be observed in PBI/ZnO hybrids. In sharp contrast, incorporation of electron-rich oligothiophene (<i>n</i>T, <i>n</i> = 1, 2) moieties into PBI core at bay positions resulted in a highly efficient cascade IET in <i>n</i>T-PBI/ZnO (<i>n</i> = 1, 2) hybrid nanorods, which was initiated by photoinduced electron transfer (PET) from <i>n</i>T (<i>n</i> = 1, 2) to PBI and then followed by charge shifting from PBI anion to ZnO across the interface. High performance UV–vis photodetectors based on <i>n</i>T-PBI/ZnO (<i>n</i> = 1, 2) hybrids have been fabricated and show responsivity of 21.2 and 12.4 A/W and an on/off ratio as high as 537 and 403, whereas that based on PBI/ZnO shows little visible-light response. Our results suggest that donor–acceptor type compounds can be used for constructing photoactive hybrid nanomaterials, in which efficient cascade IET modifies interfacial electronic structure and helps extend the spectral response range

Phase- and Shape-Controlled Synthesis of Single Crystalline Perylene Nanosheets and Its Optical Properties

Two-dimensional single-crystalline nanostructures of perylene with uniform square and rhombus shapes have been prepared successfully via a simple reprecipitation method with the assistance of surfactant CTAB templates. The X-ray diffraction (XRD) measurements reveal that the square and rhombus nanosheets can be indexed to α- and β-phase perylene crystals, respectively. On the basis of the analysis of time-dependent growth processes, we found that selective adhesion of CTAB molecules on the crystal (001) plane facilitates to the formation of sheetlike structures, whereas polymorph transition from α- to β-phase achieved by altering the surfactant CTAB concentration results in the evolution of the nanosheet from square to rhombus morphologies. Single-nanoparticle spectrscopy depicts that square and rhombus nanosheets show distinct shape-dependent optical properties that are directly related to their crystal structures. Furthermore, the optical waveguiding behaviors have been revealed through the scanning near-field optical microscopy (SNOM) technique. This expands the optical waveguides from 1D to 2D nanostructures and has a potential application in novel optoelectronic devices

Donor-Linked Di(perylene bisimide)s: Arrays Exhibiting Fast Electron Transfer for Photosynthesis Mimics

The first example of donor-linked di­(perylene bisimide)­s is reported. UV–vis absorption spectra of these newly synthesized dyads showed intense absorption across the entire visible region, demonstrating their excellent light-harvesting activities. The severe fluorescence quenching event probed by steady-state fluorescence spectroscopy and the free-energy calculations suggested the possibility of electron transfer (ET) in these arrays upon photoexcitation. Further femtosecond transient absorption spectra clarified that the fluorescence quenching was due to fast intramolecular ET. The rate of the charge separation (CS) was found to be as high as 10¹² s^–1 in CH₂Cl₂. It was suggested that the large ET driving forces, strong donor–acceptor electronic coupling, and relatively small reorganization energy of diPBI accounted for the rapid ET process in a synergic manner. The fate of the generated radical ion pair depended on the solvent used. Rapid charge recombination to ground state occurred for the dyads in polar CH₂Cl₂ and for diPBI-TPA in nonpolar toluene. However, sufficient ³diPBI* population was attained via efficient spin–orbit coupled intersystem crossing from the charge-separated state for diPBI-PdTPP in toluene. These photophysical properties are interpreted as the cooperation between thermodynamic feasibility and kinetic manipulation

Fullerene Hollow Microspheres Prepared by Bubble-Templates as Sensitive and Selective Electrocatalytic Sensor for Biomolecules

We developed an electrocatalytic sensor based on C60 hollow microspheres for highly sensitive and selective detection of dopamine (DA) in the presence of ascorbic acid (AA), and uric acid (UA) in the presence of l-cysteine (RSH). The hollow microspheres of C60 with a diameter controllable in the range of 0.5 to 1.5 μm and a thickness of 200 nm are synthesized by a high-temperature reprecipitation method with the assistance of alcohol bubbles. The superhydrophobicity of C60 hollow microspheres makes them capable of forming a compact thin film at air/water interface, which can be readily transferred on the surface of gold or glassy carbon electrodes. This porous C60 film made from C60 hollow microspheres shows a specific surface area as high as 107 m2 g–1. In order to obtain a conducting film, the C60-modified electrode is pretreated by scanning the potential range from 0.0 to −1.5 V in 1 M KOH followed by potential cycling between 550 to −50 mV in a pH 7.2 phosphate buffer solution. On the basis of XPS and IR measurements, we found that surface oxides, such as −OH and CO groups, are introduced on the surfaces of the conducting C60 film. This, combined with the porosity that enhances the adsorption activity of C60-modified electrodes, enable the electrocatalytic analysis of target biomolecules with detection limit as low as 0.1 nM for DA in the presence of AA, and 1 μM for UA in the presence of RSH

Self-Assembly of Perylenediimide Nanobelts and Their Size-Tunable Exciton Dynamic Properties

Upon the oxidation of perylenediimide dianion precursors, controlled release of neutral units paves the way for the solution-phase self-assembly of nanobelts via synergistic π–π stacking and hydrogen-bonding interactions. The obtained belt size has been regulated through adjusting the precursor supersaturation. This controlled synthesis also offers us an opportunity to explore size-tunable exciton dynamics features in the nanobelt, in which the competitive evolution to H-like exciton or excimer is found to be in strong relevance to the molecular packing and crystal size

Naphthalenediimide-Benzothiadiazole Copolymer Semiconductors: Rational Molecular Design for Air-Stable Ambipolar Charge Transport

Rational design of air-stable ambipolar polymeric semiconductors was achieved by covalently connecting naphthalenediimide (NDI) units with benzothiadiazole (BZ) through thiophene (T) linkers, namely, <b>PNDI-</b><i><b>mT</b></i><b>(BZ)</b><i><b>mT</b></i> (<i>m</i> = 1, 2), in which well-coplanar <i><b>mT</b></i><b>(BZ)</b><i><b>mT</b></i> moieties as a whole act as donors rather than acceptors reported in previous studies. Decreasing the number of thiophene linkers from <i>m</i> = 2 to 1 lowers both LUMO and HOMO energy levels. As a result, the carriers in organic thin film transistors (OTFTs) could be switched from unipolar <i>p</i>-channel only to ambipolar transport. In ambient conditions, <b>PNDI-</b><i><b>2T</b></i><b>(BZ)</b><i><b>2T</b></i> presents an average hole mobility of 0.07 ± 0.02 cm² V^–1 s^–1, while <b>PNDI-</b><i><b>T</b></i><b>(BZ)</b><i><b>T</b></i> exhibits balanced ambipolar charge transport in a bottom-gate/top-contact device architecture, the average electron and hole mobilities was 0.05 ± 0.02 (<i>μ</i>_e) and 0.1 ± 0.03 (<i>μ</i>_h) cm² V^–1 s^–1, respectively. Moreover, OTFTs based on both polymer show good air-stability with negligible changes after stored in ambient over 3 months