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Assuming a delta pulse excitation, quantum wavepackets are propagated on the excited state manifold in the energy range from 3.4–5.0 eV for coronene and 2.4–3.5 eV for circumcoronene to study the time evolution of the states as well as their lifetimes. The full-dimensional (102 and 210 degrees of freedom for coronene and circumcoronene respectively) non-adiabatic dynamics simulated with the ML-MCTDH method on twelve coupled singlet electronic states show that the different absorption spectra are only due to electronic delocalisation effects that change the excited state energies, but the structural dynamics in both compounds are identical. Breathing and tilting motions drive the decay dynamics of the electronic states away from the Frank–Condon region independently of the size of the aromatic system. This promising result allows the use of coronene as a model system for the dynamics of larger polycyclic aromatic hydrocarbons (PAHs) and graphene one dimensional sheets or nanoflakes. [ABSTRACT FROM AUTHOR]

To respond to the constant miniaturization of modern devices, it is imperative to develop novel classes of hybrid materials with outstanding functionalities. One of the most promising developments in this regard is photoswitchable nanoelectronics, which offer non-invasive structural changes via irradiation. Azobenzenes, in particular, represent a widely investigated group of compounds due to their reversible photoisomerization and flexibility to introduce modifications by functionalizing the aryl ring. Here, an interface consisting of graphene quantum dots (GQDs) and a pyrene functionalized azobenzene (AZO) is built and investigated to unravel the energy and charge transfer dynamics at play. The influence of the conformation, isomerization and thermal effects on the photophysics is described using a multiscale computational approach coupled to electronic structure calculations. By computing the photoinduced energy and charge transfer rates we found that the small exciton reorganization energy and favorable alignment of the energy levels at the interface favor excitation energy transfer. A significant increase of photoinduced hole transfer from AZO to GQDs is observed when thermal effects are considered. Moreover, these photoinduced processes for the azobenzene molecules in their trans configuration are always faster than those related to the cis isomer. This is due to a favorable overlap and a stronger interaction of the trans isomer, considered the active state, with the GQDs. On the other hand, the cis configuration, featuring slower photoinduced energy and charge transfer processes, can be considered as the inactive species. Nevertheless, its contribution to the overall photophysics remains non-negligible. [ABSTRACT FROM AUTHOR]

Multicolor emissive carbon dots (CDs) hold great potential for a wide range of applications in various fields. However, the luminescence enhancement mechanism is still controversial due to combined effects of the carbon core and surface states. Herein, we elucidate the surface state mechanism for the tunable and enhanced photoluminescence of CDs via only surface nitrogen and sulfur modification (N,S-CDs) through an electrochemical synthesis method. It is demonstrated that surface nitrogen functionalization with increasing content of NH2 groups leads to multicolor emission from blue to red. Moreover, surface sulfur functionalization with the introduction of C–S bonds can further improve the luminescence intensity by facilitating the transition of S-related excitation electrons and radiative recombination. In addition, the high luminance of N,S-GCDs enables their application in flexible fluorescence films, latent fingerprint detection and information encryption. [ABSTRACT FROM AUTHOR]

A molecular imprinted polymer (MIP) fabricated from a chitosan doped with graphite to create a conductive composite (CG-MIC) with the ability to trap and detect dimethyl methylphosphonate (DMMP) through a change in resistance of the material has been successfully manufactured. The GC-MIC presented a maximum trapping capacity of 96 ppm (0.096 mg g−1) of DMMP. A similar non-imprinted composite made of chitosan-graphite (CG-NIC) had a surface adsorption of 48 ppm (0.048 mg g−1) of DMMP. The manufacturing process was tested for consistency and there were no significant differences in resistance between batches of CG-MIC before (around 450 Ω) and after (around 70 Ω) DMMP extraction, representing a homogeneous manufacturing process. Although Atomic Force Microscopy studies revealed that the graphite was not homogenously distributed throughout the chitosan matrix, the response was consistent. The changes in the concentration of DMMP within the self-sensing material, being proportional to those in gas concentration, could be followed by the changes in resistance. The inclusion of common interferents: Acetic acid, acetone, ethanol, ammonium hydroxide and 2-propanol, equivalent in concentration to the DMMP, caused a change in the resistance of the material but did not substantially affect the specific resistance response of the composite material. Based on this data, the CG-MIC could be used as a smart material with sensing capabilities to monitor trapping levels of DMMP. [ABSTRACT FROM AUTHOR]

Urgent requirements for high-efficiency and low-cost photovoltaic devices are constantly pushing forward the development of emerging solar cells. Currently, organic solar cells (OSCs) and perovskites solar cells (PSCs) are considered most likely commercialized solar cells in the short-term period. Enormous optimization strategies towards optimizing the device efficiency and stability have been developed. It is noteworthy that the well-known small-sized quantum dots (QDs) have been explored as the additional components in OSCs and PSCs, and have yielded rather modest amelioration of the device performance. Herein, we reviewed recent advances in strategically integrating all kinds of QDs (consisting of metal chalcogenide-based QDs, perovskite QDs, InP-based QDs, carbon QDs, graphene QDs, black phosphorus QDs, and other emerging two-dimensional QDs) and the associated relevant performance enhancement of OSCs and PSCs. In view of each type of QDs, we have mainly emphasized their involved device configuration, integration location, and physical mechanism. In addition, the fundamental structures, operation principles, and analogies/distinctions of OSCs and PSCs have been briefly outlined. Finally, existing challenges and future prospects based on QDs-integrated OSCs and PSCs have been listed. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) integrated with two-dimensional (2D) nanomaterials hold potential use in photodetector devices due to the unique light absorption of QDs and excellent carrier transport properties of 2D nanomaterials. A simple strategy to fabricate hybrid graphene and QD photodetectors using a single-crystal monolayer graphene film as a carrier channel at the top and perfectly wrapping it to be in contact with the bottom layer of C3N QDs is developed. This strategy can lead to a tight contact between C3N QDs and the graphene interface, thus facilitating an efficient collection of all photo-generated carriers. Photodetectors, employing C3N QDs integrated with single-crystal graphene, exhibited distinct photocurrent response with high responsivity and detectivity at 1550 nm. The photocurrent map and simulated electric field distribution reveal the fast response and recovery, indicating that C3N QDs enhanced the local electric field near graphene. The present research indicates the strategy of combining hybrid architectures for optoelectronic devices to improve their performance thereof. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) are promising materials for biomedical applications owing to their unique properties, biocompatibility, and biodegradability. The current studies on CDs are focused on improving their functionality by modulating their electronic structure, which helps in controlling their chemical, optical, and electrical properties. Doping with heteroatoms is a typical approach for modulating the electronic structure of CDs. In particular, there has been considerable progress in nitrogen-doped CDs for improving their potential for various biomedical applications, including optical imaging, drug delivery, and light-mediated imaging/therapeutic applications such as photoacoustic imaging, photothermal therapy, and photodynamic therapy. In this review, the important features of nitrogen-doped CDs are discussed along with the recent studies on these materials and their prospects. [ABSTRACT FROM AUTHOR]

The fluorescence solvatochromism of p-phenylenediamine-derived carbon dots (CDs) was modulated through surface modification with decanoic acid or perfluorodecanoic acid. This is attributed to the adjustment of the dipole interaction between solvent molecules and the CD surface in terms of steric hindrance of a surface modifier and polarization of the modified CD surface. [ABSTRACT FROM AUTHOR]

A crystalline quantum dot of a COF was prepared for the first time by the original BRB method and a novel pathway for online monitoring of the COF reaction rate was proposed. The quantum dot can respond to uranyl ion quickly and sensitively and is of great potential in uranium detection. [ABSTRACT FROM AUTHOR]

A portable linear ion trap mass spectrometer featuring a compact three-stage vacuum system, a continuous atmospheric pressure interface (CAPI), and a miniature ion funnel was developed and characterized. The dimensions and weight of the instrument were 38 × 26 × 23 cm3 and ∼20 kg, respectively. The combination of a three-stage vacuum system and CAPI reduced the pressure smoothly from atmospheric to ∼5 × 10−4 Torr, ensuring that the miniature ion funnel, quadrupole ion guide, and linear ion trap operated in a suitable and stable vacuum environment. The analytical performance of the instrument was evaluated with a nano-electron spray ionization source and a reserpine sample solution. A satisfactory mass resolution up to 4060 (m/Δm, FWHM) was achieved at m/z 609 when the mass scan rate was 495 Da s−1. Unit mass resolution was achieved at a mass scan rate of 6000 Da s−1. In addition, a limit of detection of 5 ng mL−1 was achieved and tandem mass spectrometry (MS3) was successfully performed with the instrument. Furthermore, the measurements showed high repeatability and stability (RSD < 6%). This portable mass spectrometer shows great potential for practical applications in on-site analyses, such as those required for food safety, drug analysis, environmental protection, forensic investigations, and homeland security. [ABSTRACT FROM AUTHOR]

Reported is a confined lattice plane electrochemical exfoliation method that exploits the electrochemical reaction of face (basal) or side (edge) planes of highly oriented pyrolytic graphite (HOPG) while other planes are blocked using wax, based on the anisotropy of HOPG for efficient and effective fabrication of graphene nanodots with uniform size distribution. [ABSTRACT FROM AUTHOR]

The emergence of carbon dots (CDs) has opened up an exciting new field in the science and technology of carbon nanomaterials and has attracted increasing interest in recent years. Due to their diverse physicochemical properties and favourable attributes, such as quantum confinement effects and abundant surface defects, CDs and their derived hybrids have shown exciting and indispensable prospects in the energy conversion and storage fields. Considering the latest developments, in this review, we comprehensively summarize the classification and structure of CDs. Three strategies for structural engineering of CDs are presented and analyzed, in terms of the tuning of size and crystallinity, and the methodologies for surface modification and heteroatom doping, with a focus on the relationship among the synthesis methods, structure and properties of the concerned CDs. More importantly, the recent advances in energy-oriented applications of CDs, including photo- and electro-catalysis, light-emitting diodes, photovoltaic cells, lithium/sodium ion batteries and supercapacitors, will be systematically highlighted. Finally, we discuss and outline the remaining major challenges and opportunities for CDs in the future. [ABSTRACT FROM AUTHOR]

Solution-processable graphene derivatives, such as graphene oxide (GO) and graphene quantum dots (GQDs), are a promising class of cathode interlayer (CIL) materials for polymer solar cells (PSCs). These graphene derivatives always contain ions, which may migrate under electrical field during the PSC device operation and consequently deteriorate device stability. In this manuscript, by functionalizing GQDs with amino N-oxide groups at the edge of the graphene basal plane, we develop a non-ionic graphene derivative (GQD-NO) as a CIL. The periphery polar amino N-oxide groups form the desired interfacial dipole with an indium tin oxide (ITO) electrode to lower the work function by as much as 1.06 eV. As a result, GQD-NO as a CIL forms Ohmic contact with the active layer of PSC devices, improves electron transport/extraction, blocks holes and prevents charge recombination on the cathode. Owing to the periphery amino N-oxide groups, GQD-NO exhibits good solubility in water and insolubility in common low-polarity organic solvents, which enables multilayer inverted PSC device fabrication. In addition, the small lateral size of GQD-NO leads to a large bandgap and transparency in the visible/NIR region. Using a blend of poly[N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-thienyl-2,1,3-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the active layer, the inverted PSC device with GQD-NO as CIL shows the power conversion efficiency of 7.43%, which is much higher than that with the state-of-the-art ZnO as CIL (PCE = 6.56%) or without the CIL (PCE = 3.16%). These results indicate that non-ionic GQD-NO is a promising CIL for PSCs. [ABSTRACT FROM AUTHOR]

Recent years have witnessed a cornucopia of synthetic methods for fabricating carbon–metal nanocomposites. Nonetheless, achieving a cooperative synergy of zero-dimensional carbon nanomaterials and metal nanocrystals is still uncommon. To this end, we performed a controllable structural design comprising customizable alternating layers of active and functional zero-dimensional nanomaterials, which were intimately assembled together. This unique highly-ordered multilayer configuration was afforded by a judicious layer-by-layer (LbL) assembly strategy, enabling the rational and tunable construction of a series of well-defined metal/graphene quantum dots (M/GQDs)n (M = Au, Ag, Pt) multilayers. This strategy allows the direct assembly of customized units of positively-charged graphene quantum dots (GQDs) and negatively-charged metal nanocrystals (NCs), which were integrated in an alternating stacked fashion under a pronounced electrostatic attractive interaction. Moreover, these multilayer thin films demonstrate remarkably efficient and versatile catalytic performance toward the selective organic transformation of aromatic nitro compounds, electrocatalytic methanol oxidation and photoelectrochemical water splitting under simulated solar light irradiation under ambient conditions, attributed to the cooperative synergy of the metal NC and GQD building blocks. More significantly, the catalytic performances of the (M/GQDs)n (M = Au, Ag, Pt) multilayer thin films are tunable via the assembly cycle and sequence, as well as by selecting different metal NC types. This work highlights the significance of the customizable design of GQDs–metal-based systems for various advanced chemical-to-energy conversion applications. [ABSTRACT FROM AUTHOR]

The development of two-dimensional (2D) inorganic materials-based quantum dots (QDs) is still in its infancy but is triggering immense enthusiasm due to their high chemical stability, good aqueous dispersibility, excellent optical property, good biocompatibility and easy functionalization. This review covers almost all the extant 2D-QDs based on graphene, phosphorene, silicene, carbides, nitrides, transition metal dichalcogenide, transition metal oxides and MXenes, etc. Their categories, synthetic routes, properties, functionalization and applications are critically highlighted. In the application section, special emphasis is placed on the progress in bioimaging, cancer therapy, fluorescent sensing and optoelectronics. Meanwhile, the latest advances in 2D QDs-based catalysis and energy since 2015 are addressed. Moreover, 2D nanoclusters, in particular 2D-QDs, are also included. This review provides guidance for 2D-QDs studies to meet the increasing demands in the many diverse applications. [ABSTRACT FROM AUTHOR]

Herein, we summarize recent research developments and progress of carbon dots (CDs), which have been attracting considerable attention as a new type of photoluminescent material. Raw materials, from single carbonaceous compounds to colorful natural substances, for the synthesis of CDs are discussed. A range of diverse synthetic methodologies to achieve better photoluminescence performance and more advanced functions are summarized, and these are basically divided into two classes: top-down and bottom-up. The inspiring properties, mainly including composites, optical properties and cytotoxicity, are listed. In particular, the luminescence mechanism and surface functionalization of the CDs are briefly discussed. Moreover, on the basis of the above, the long-wavelength and multicolor emission properties of CDs and ways to achieve these goals including surface state and size controlled by synthesis strategies, proper precursors, chemical doping and modification, solvatochromic effects and energy transfer are reviewed in detail. [ABSTRACT FROM AUTHOR]

Solid-phase microextraction (SPME) is directly integrated with low temperature plasma ionisation mass spectrometry to rapidly detect organophosphate chemical warfare agent simulants and their hydrolysis products in chemical mixtures, including urine. In this sampling and ionization method, the fibre serves: (i) to extract molecules from their native environment, and (ii) as the ionization electrode that is used to desorb and ionize molecules directly from the SPME surface. By use of a custom fabricated SPME fibre consisting of a stainless steel needle coated with a Linde Type A (LTA) zeolitic microporous material and low temperature plasma mass spectrometry, protonated dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP) and pinacolyl methylphosphonic acid (PinMPA) can be detected at less than 100 ppb directly in water and urine. Organophosphates were not readily detected by this approach using an uncoated needle in negative control experiments. The use of the LTA coating significantly outperformed the use of a high alumina Zeolite Socony Mobil-5 (ZSM-5) coating of comparable thickness that is significantly less polar than LTA. By conditioning the LTA probe by immersion in an aqueous CuSO4 solution, the ion abundance for protonated DMMP increased by more than 300% compared to that obtained without any conditioning. Sample recovery values were between 96 and 100% for each analyte. The detection of chemical warfare agent analogues and hydrolysis products required less than 2 min per sample. A key advantage of this sampling and ionization method is that analyte ions can be directly and rapidly sampled from chemical mixtures, such as urine and seawater, without sample preparation or chromatography for sensitive detection by mass spectrometry. This ion source should prove beneficial for portable mass spectrometry applications because relatively low detection limits can be obtained without the use of compressed gases, fluid pumps, and lasers. Moreover, the ion source is compact, can be powered with a 10 V battery, and is tolerant of complex mixtures. [ABSTRACT FROM AUTHOR]

Covering: up to 2015 This review summarises the accumulated knowledge about characterised bacterial terpene cyclases. The structures of identified products and of crystallised enzymes are included, and the obtained insights into enzyme mechanisms are discussed. After a summary of mono-, sesqui- and diterpene cyclases the special cases of the geosmin and 2-methylisoborneol synthases that are both particularly widespread in bacteria will be presented. A total number of 63 enzymes that have been characterised so far is presented, with 132 cited references. [ABSTRACT FROM AUTHOR]