Activated Singlet Fission Dictated by Anti-Kasha Property in a Rylene Imide Dye.

A key challenge in the search of new materials capable of singlet fission (SF) arises from the primary energy conservation criterion, i.e., the energy of the triplet exciton has to be half that of the singlet (E(S1) ≥ 2E(T1)), which excludes most photostable organic materials from consideration and confines the design strategy to materials with low energy triplet states. One potential way to overcome this energy requirement and improve the triplet energy is to enable a SF channel from higher energy ("hot") excitonic states (Sn) in a process called activated SF. Herein, we demonstrate that efficient activated SF is achieved in a rylene imide-based derivative acenaphth[l, 2-a]acenaphthylene diimide (AADI). This process is enabled by an increase in the energy gap to greater than 1.0 eV between the S3 and S1 states due to the incorporation of an antiaromatic pentalene unit, which leads to the emergence of anti-Kasha properties in the isolated molecule. Transient spectroscopy studies show that AADI undergoes ultrafast SF from higher singlet excited states in thin film, with excitation wavelength-dependent SF yields. The SF yield of ∼200% is observed upon higher energy excitation, and long-lived free triplets persist on the µs time scale suggesting that AADI can be used in SF-enhanced devices. Our results suggest that enlarging the Sn-S1 energy gap is an effective way to turn on the activated SF channel and shed light on the development of novel, stable SF materials with high triplet energies.

High-Efficiency 3D-Printed Three-Chamber Electromagnetic Peristaltic Micropump.

This paper describes the design and characteristics of a three-chamber electromagnetic-driven peristaltic micropump based on 3D-printing technology. The micropump is composed of an NdFeB permanent magnet, a polydimethylsiloxane (PDMS) film, a 3D-printing pump body, bolts, electromagnets and a cantilever valve. Through simulation analysis and experiments using a single chamber and three chambers, valved and valveless, as well as different starting modes, the results were optimized. Finally, it is concluded that the performance of the three-chamber valved model is optimal under synchronous starting conditions. The measurement results show that the maximum output flow and back pressure of the 5 V, 0.3 A drive source are 2407.2 µL/min and 1127 Pa, respectively. The maximum specific flow and back pressure of the micropump system are 534.9 µL/min∙W and 250.4 Pa/W, respectively.

A Flexible Thermocouple Film Sensor for Respiratory Monitoring.

A novel flexible thermocouple film sensor on a polyimide substrate is proposed that is simple and flexible for monitoring the respiratory signal. Several thermocouples were connected in series and patterned on the polyimide substrate, and each one is formed by copper and a constant line connected to each other at two nodes. The respiratory signal was measured by the output voltage, which resulted from the temperature difference between the hot and cold junctions. The sensors were fabricated with surface-microfabrication technology with three sputtering steps. The measurement results showed that the peak voltage decreased by 90% in the case of apnea compared with normal breathing. The sensor has potential application for wearable detection of sleep apnea hypopnea syndrome (OSAHS).

Fluorescence-based thermal sensing with elastic organic crystals.

Operation of temperature sensors over extended temperature ranges, and particularly in extreme conditions, poses challenges with both the mechanical integrity of the sensing material and the operational range of the sensor. With an emissive bendable organic crystalline material, here we propose that organic crystals can be used as mechanically robust and compliant fluorescence-based thermal sensors with wide range of temperature coverage and complete retention of mechanical elasticity. The exemplary material described remains elastically bendable and shows highly linear correlation with the emission wavelength and intensity between 77 K to 277 K, while it also transduces its own fluorescence in active waveguiding mode. This universal new approach expands the materials available for optical thermal sensing to a vast number of organic crystals as a new class of engineering materials and opens opportunities for the design of lightweight, organic fluorescence-based thermal sensors that can operate under extreme temperature conditions such as are the ones that will be encountered in future space exploration missions.

Enhancing Transition Dipole Moments of Heterocyclic Semiconductors via Rational Nitrogen-Substitution for Sensitive Near Infrared Detection.

Designing ultrastrong near-infrared (NIR) absorbing organic semiconductors is a critical prerequisite for sensitive NIR thin film organic photodetectors (OPDs), especially in the region of beyond 900 nm, where the absorption coefficient of commercial single crystalline silicon (c-Si) is below 103 cm-1 . Herein, a pyrrolo[3,2-b]thieno[2,3-d]pyrrole heterocyclic core (named as BPPT) with strong electron-donating property and stretched geometry is developed. Relative to their analogue Y6, BPPT-contained molecules, BPPT-4F and BPPT-4Cl, show substantially upshifted and more delocalized highest occupied molecular orbitals, and larger transition dipole moments, leading to bathochromic and hyperchromic absorption spectra extending beyond 1000 nm with very large absorption coefficients (up to 3.7-4.3 × 105 cm-1 ) as thin films. These values are much higher than those (104 to 1 × 105 cm-1 ) of typical organic semiconductors, and 1-2 orders higher than those of commercial inorganic materials, such as c-Si, Ge, and InGaAs. The OPDs based on BPPT-4F or BPPT-4Cl blending polymer PBDB-T show high detectivity of above 1012 Jones in a wide wavelength range of 310-1010 nm with excellent peak values of 1.3-2.2 × 1013 Jones, respectively, which are comparable with and even better than those commercial inorganic photodetectors.

Design, Simulation and Experimental Study of the Linear Magnetic Microactuator.

This paper reports the design, simulation and experimental study of a linear magnetic microactuator for portable electronic equipment and microsatellite high resolution remote sensing technology. The linear magnetic microactuator consists of a planar microcoil, a supporter and a microspring. Its bistable mechanism can be kept without current by external permanent magnetic force, and can be switched by the bidirectional electromagnetic force. The linearization and threshold of the bistable mechanism was optimized by topology structure design of the microspring. The linear microactuator was then fabricated based on non-silicon technology and the prototype was tested. The testing results indicated that the bistable mechanism was realized with a fast response of 0.96 ms, which verified the simulation and analysis.

Effects of maltose and lysine treatment on coffee aroma by flash gas chromatography electronic nose and gas chromatography-mass spectrometry.

BACKGROUND: Arabica coffee is a sub-tropical agricultural product in China. Coffee undergoes a series of thermal reactions to form abundant volatile profiles after roasting, so it loses a lot of reducing sugars and amino acids. Adding carbonyl compounds with amino acids before roasting could ensure the nutrition and flavour of coffee. The technology is versatile for the development of coffee roasting process. This investigation evaluates the effects of combining maltose and lysine (Lys) to modify coffee aroma and the possibly related mechanisms. Arabica coffee was pretreated with a series of solvent ratios of maltose and Lys with an identical concentration (0.25 mol L-1 ) before microwave heating. RESULTS: It was found that the combination of maltose and Lys significantly (P ≤ 0.05) influenced quality indices of coffee (pH and browning degree). Ninety-six aromatic volatiles have been isolated and identified. Twelve volatile profiles revealed the relationship between fragrance difference and compound content in coffee. Moreover, coffee aroma was modified by a large number of volatiles with different chemical classes and character. CONCLUSION: Thus, our results suggest that the combination of reagents changed overall aroma quality through a series of complex thermal reactions, especially the ratio of Lys/maltose over 2:1. © 2017 Society of Chemical Industry.

The structure features of umami hexapeptides for the T1R1/T1R3 receptor.

Umami is thought to be initiated by binding tastants to G-protein-coupled receptors in taste cells, while the structure and mechanism of the receptors are not clear. In this study, we summarized umami peptides and classified them roughly into two groups: the first group contains dipeptides and tripeptides with terminal Glu or Asp, while the second peptides comprises more amino acids without significant features. The research on the structure and taste characteristics of second group peptides are less studied, so we focus on this group. In this work, nine flavor peptides were newly identified from Takifugu obscurus, and among them, the umami hexapeptides KGRYER belong to the second group. Five hexapeptides from this study, our previous work and references were chosen to build a Three Dimensional Quantitative Structure-Activity Relationship model with q2 value as 0.964 successfully. Then the relationship between the structure and intensity of umami peptides were illustrated.

Large Out-of-Plane Displacement Bistable Electromagnetic Microswitch on a Single Wafer.

This paper presents a bistable microswitch fully batch-fabricated on a single glass wafer, comprising of a microactuator, a signal transformer, a microspring and a permanent magnet. The bistable mechanism of the microswitch with large displacement of 160 µm depends on the balance of the magnetic force and elastic force. Both the magnetic force and elastic force were optimized by finite-element simulation to predict the reliable of the device. The prototype was fabricated and characterized. By utilizing thick laminated photoresist sacrificial layer, the large displacement was obtained to ensure the insulation of the microswitch. The testing results show that the microswitch realized the bistable mechanism at a 3-5 V input voltage and closed in 0.96 ms, which verified the simulation.