Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)] (where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

It is demonstrated that 3D nanostructured polypyrrole (3D PPy) nanocomposites can be reinforced with PPy covered nanocellulose (PPy@nanocellulose) fibres to yield freestanding, mechanically strong and porosity optimised electrodes with large surface areas. Such PPy@nanocellulose reinforced 3D PPy materials can be employed as free-standing paper-like electrodes in symmetric energy storage devices exhibiting cell capacitances of 46 F g(-1), corresponding to specific electrode capacitances of up to ∼185 F g(-1) based on the weight of the electrode, and 5.5 F cm(-2) at a current density of 2 mA cm(-2). After 3000 charge/discharge cycles at 30 mA cm(-2), the reinforced 3D PPy electrode material also showed a cell capacitance corresponding to 92% of that initially obtained. The present findings open up new possibilities for the fabrication of high performance, low-cost and environmentally friendly energy-storage devices based on nanostructured paper-like materials.

In order to test the statistical influence of some process and micromachining parameters on the fracture strength of silicon microelements, arrays of identical microsized cantilever beams were bulk micromachined in single-crystalline silicon wafers. The beams were exposed to various surface treatments (diamond polishing with different grades, oxidization, stripping of oxide) in different combinations. The influence on fracture strength was investigated by bending the beams to fracture in a micromanipulator mounted in situ in a scanning electron microscope while registering force-versus-deflection curves. Average fracture strengths, standard deviations, Weibull moduli, crack-initiating flaw sizes, and in some cases elastic moduli were evaluated. Diamond polishing was found to decrease the fracture strength drastically, but polishing followed by oxidization not only restored the original strength, but actually increased it, due to crack healing. Polishing, oxidization, and subsequent stripping of oxide resulted in fracture strengths slightly higher than the original strength. The Weibull modulus was diminished from 10 to 6–9 by the polishing. The initiating flaw sizes were theoretically evaluated, and found to agree with previous results of cross-sectional transmission electron microscopy studies of polished silicon surfaces. The elastic moduli determined were significantly lower (30%–40%) than the corresponding module of pure, single-crystalline silicon, probably due to high dopant contents in the specimens investigated here.