Ian D. Williams

How are WEEE doing? A global review of the management of electrical and electronic wastes

This paper presents and critically analyses the current waste electrical and electronic equipment (WEEE) management practices in various countries and regions. Global trends in (i) the quantities and composition of WEEE; and (ii) the various strategies and practices adopted by selected countries to handle, regulate and prevent WEEE are comprehensively examined. The findings indicate that for (i), the quantities of WEEE generated are high and/or on the increase. IT and telecommunications equipment seem to be the dominant WEEE being generated, at least in terms of numbers, in Africa, in the poorer regions of Asia and in Latin/South America. However, the paper contends that the reported figures on quantities of WEEE generated may be grossly underestimated. For (ii), with the notable exception of Europe, many countries seem to be lacking or are slow in initiating, drafting and adopting WEEE regulations. Handling of WEEE in developing countries is typified by high rate of repair and reuse within a largely informal recycling sector. In both developed and developing nations, the landfilling of WEEE is still a concern. It has been established that stockpiling of unwanted electrical and electronic products is common in both the USA and less developed economies. The paper also identifies and discusses four common priority areas for WEEE across the globe, namely: (i) resource depletion; (ii) ethical concerns; (iii) health and environmental issues; and (iv) WEEE takeback strategies. Further, the paper discusses the future perspectives on WEEE generation, treatment, prevention and regulation. Four key conclusions are drawn from this review: global amounts of WEEE will continue unabated for some time due to emergence of new technologies and affordable electronics; informal recycling in developing nations has the potential of making a valuable contribution if their operations can be changed with strict safety standards as a priority; the pace of initiating and enacting WEEE specific legislation is very slow across the globe and in some cases non-existent; and globally, there is need for more accurate and current data on amounts and types of WEEE generated.

Switching the light emission of (4-biphenylyl)phenyldibenzofulvene by morphological modulation: crystallization-induced emission enhancement

(4-Biphenylyl)phenyldibenzofulvene is weakly luminescent in the amorphous phase but becomes highly emissive upon crystallization; this unusual crystallization-induced emission enhancement effect allows its emission to be repeatedly switched between dark and bright states by fuming-heating and heating-cooling processes.

Synergy between Twisted Conformation and Effective Intermolecular Interactions: Strategy for Efficient Mechanochromic Luminogens with High Contrast

A strategy towards efficient mechanochromic luminogens with high contrast is developed. The twisted propeller-like conformations and effective intermolecular interactions not only endow the luminogens with AIE characteristics and high efficiency in the crystalline state, but also render them to undergo conformational planarization and disruption in intermolecular interactions upon mechanical stimuli, resulting in remarkable changes in emission wavelength and efficiency.

Molecular anchors in the solid state: Restriction of intramolecular rotation boosts emission efficiency of luminogen aggregates to unity

Introduction of freely rotatable tetraphenylethene (TPE) to conventional luminophors quenches their light emissions in the solutions but endows the resultant molecules (TPEArs) with aggregation-induced emission characteristics in the condensed phase due to the restriction of intramolecular rotation. High fluorescence quantum yields up to 100% have been achieved in the films of TPEArs.

Benzothiazolium-functionalized tetraphenylethene: an AIE luminogen with tunable solid-state emission.

Melding a benzothiazolium unit with tetraphenylethene generates a new hemicyanine luminogen with aggregation-induced emission characteristics; the luminogen exhibits crystochromism and its solid-state emission can be repeatedly tuned from yellow or orange to red by grinding-fuming or grinding-heating processes due to the transformation from the crystalline to the amorphous state and vice versa.

Fluorescent Bioprobes: Structural Matching in the Docking Processes of Aggregation-Induced Emission Fluorogens on DNA Surfaces

Whereas most conventional DNA probes are flat disklike aromatic molecules, we explored the possibility of developing quadruplex sensors with nonplanar conformations, in particular, the propeller-shaped tetraphenylethene (TPE) salts with aggregation-induced emission (AIE) characteristics. 1,1,2,2-Tetrakis[4-(2-triethylammonioethoxy)phenyl]ethene tetrabromide (TPE-1) was found to show a specific affinity to a particular quadruplex structure formed by a human telomeric DNA strand in the presence of K(+) ions, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Steady-state and time-resolved spectral analyses revealed that the specific binding stems from a structural matching between the AIE fluorogen and the DNA strand in the folding process. Computational modeling suggests that the AIE molecule docks on the grooves of the quadruplex surface with the aid of electrostatic attraction. The binding preference of TPE-1 enables it to serve as a bioprobe for direct monitoring of cation-driven conformational transitions between the quadruplexes of various conformations, a job unachievable by the traditional G-quadruplex biosensors. Methyl thiazolyl tetrazolium (MTT) assays reveal that TPE-1 is cytocompatible, posing no toxicity to living cells.

Pyrene-substituted ethenes: aggregation-enhanced excimer emission and highly efficient electroluminescence

Pyrene-substituted ethenes, 1,2,2-tripheny-1-pyrenylethene (TPPyE) and 1,2-diphenyl-1,2-dipyrenylethene (DPDPyE), are synthesized and characterized. Whereas they are weakly emissive in solution they become strong emitters when aggregated in the condensed phase. In contrast to the general observation that excimer formation quenches the light emission of fluorophores, TPPyE and DPDPyE exhibit efficient excimer emissions in the solid state with high fluorescence quantum yields up to 100%. The π–π intermolecular interactions between the pyrene rings, coupled with multiple C–H⋯π hydrogen bonds, efficiently restrict intramolecular rotations, which block the nonradiative energy decay channel, and hence make the dye molecules highly emissive in the solid state. Non-doped organic light-emitting diodes using TPPyE and DPDPyE as emitters are fabricated, which give green light at low turn-on voltages (down to 3.2 V) with maximum luminance and power, current, and external quantum efficiencies of 49830 cd m−2, 9.2 lm W−1, 10.2 cd A−1 and 3.3%, respectively.

‘Carbon footprinting’: towards a universally accepted definition

As the threat of climate change becomes more acute, so does the need for adequate measures of impact(s), management and mitigation. Although carbon footprints are increasingly being used by organizations in the public and private sectors, a number of challenges and questions need to be addressed; among them, what does the term ‘carbon footprint’ actually mean? The term needs a universally accepted definition before a consistent, accurate, comparable and transferable methodology can be developed. This article investigates the range of current definitions proposed for a carbon footprint in the context of inventoried emissions, applications, boundaries and limitations. We argue that to only account for CO2 emissions would result in the omission of almost a third of GHGs and a significant gap in their global management, whilst inclusion of all GHGs is very time-consuming and expensive, and should be considered only in system-specific life cycle-based assessments; this requires a separate definition, name and methodology. We suggest that as data collection for CO2 and CH4 emissions is relatively straightforward, these two carbon-based gases should be used in the determination of a carbon footprint. This should allow the carbon footprint to become a cost-effective, practical and repeatable metric that can be adopted by all types of organizations across the globe as a ‘baseline’ indicator. However, it is likely that a more comprehensive metric will be required in some circumstances and by some organizations, so we also propose further GHG inclusion for full life cycle assessment-based assessments; where complete data is obtainable it can be used to provide a ‘climate footprint’. This name reflects the addition of noncarbon-based gases and encompasses the full range of gases used in the global political community’s response in managing climate change. We conclude by considering lessons learnt with the proposal of sound and pragmatic definitions.

Three coordinate phosphorus and boron as π-donor and π-acceptor moieties respectively, in conjugated organic molecules for nonlinear optics: crystal and molecular structures of E-Ph–CHCH–B(mes)2, E-4-MeO–C6H4–CHCH-B(mes)2, and E-Ph2P–CHCH–B(mes)2[mes = 2,4,6-Me3C6H2]

Hydroboration of π-donor substituted alkynes D–CC–H [D = Ph2P, 4-X–C6H4-(X = H, MeS, MeO, H2N), and (η5-C5H5)Fe(η5-C5H4-)] with dimesitylborane {[(mes)2BH]2, mes = 2,4,6-Me3C6H2} yields air-stable ‘push–pull’E-alkenes of the form E-D–CHCH–B(mes)2, which possess large molecular hyperpolarizabilities, β, as shown by electric-field induced second-harmonic generation (EFISH) experiments at 1.91 µm; single crystal X-ray diffraction studies indicate that E-Ph–CHCH–B(mes)2 and E-4-MeO–C6H4–CHCH–B(mes)2 crystallise in centrosymmetric space groups, whereas E-Ph2P–CHCH–B(mes)2 crystallises in the acentric space group P212121 and exhibits powder SHG of 1.064 µm laser light.

Fluorescent pH sensor constructed from a heteroatom-containing luminogen with tunable AIE and ICT characteristics

A heteroatom-containing organic fluorophore 1-(4-pyridinyl)-1-phenyl-2-(9-carbazolyl)ethene (CP3E) was designed and synthesized. CP3E exhibits the effect of intramolecular charge transfer (ICT) caused by the donor–acceptor interaction between its carbazole and pyridine units. Whereas it emits faintly in solution, it becomes a strong emitter in the aggregated state, demonstrating the phenomenon of aggregation-induced emission (AIE). Its emission can be reversibly switched between blue and dark states by repeated protonation and deprotonation. Such behaviour enables it to work as a fluorescent pH sensor in both solution and the solid state and as a chemosensor for detecting acidic and basic organic vapors. Analyses by NMR spectroscopy, single-crystal X-ray diffraction and computational calculations suggest that the change in electron affinity of the pyridinyl unit and molecular conformation of CP3E upon protonation and deprotonation is responsible for such sensing processes.