Patterning π‐Conjugated Polymers

π‐Conjugated polymers show promise as active materials in application areas such as microelectronics, electro‐optics, opto‐electronics, and photonics. A critical feature in this emerging technology is device fabrication and the reproducible deposition of active material. This review focuses on current trends in the spatial deposition of conjugated polymers.     

Fluorescent Nanoparticles Based on Self‐Assembled π‐Conjugated Systems

π‐Conjugated molecules are interesting components to prepare fluorescent nanoparticles. From the use of polymer chains that form small aggregates in water to the self‐assembly of small chromophoric segments into highly ordered structures, the preparation of these materials allows to develop systems with applications as sensors or biolabels. The potential functionalization of the nanoparticles can lead to specific probing. This progress report describes the recent advances in the preparation of such emittive organic nanoparticles.     

Creating Graphitic Carbon Nitride Based Donor‐π–Acceptor‐π–Donor Structured Catalysts for Highly Photocatalytic Hydrogen Evolution

Conjugated polymers with tailored donor–acceptor units have recently attracted considerable attention in organic photovoltaic devices due to the controlled optical bandgap and retained favorable separation of charge carriers. Inspired by these advantages, an effective strategy is presented to solve the main obstructions of graphitic carbon nitride (g‐C₃N₄) photocatalyst for solar energy conversion, that is, inefficient visible light response and insufficient separation of photogenerated electrons and holes. Donor‐π–acceptor‐π–donor polymers are prepared by incorporating 4,4′‐(benzoc 1,2,5 thiadiazole‐4,7‐diyl) dianiline (BD) into the g‐C₃N₄ framework (UCN‐BD). Benefiting from the visible light band tail caused by the extended π conjugation, UCN‐BD possesses expanded visible light absorption range. More importantly, the BD monomer also acts as an electron acceptor, which endows UCN‐BD with a high degree of intramolecular charge transfer. With this unique molecular structure, the optimized UCN‐BD sample exhibits a superior performance for photocatalytic hydrogen evolution upon visible light illumination (3428 µmol h^?1 g^?1), which is nearly six times of that of the pristine g‐C₃N₄. In addition, the photocatalytic property remains stable for six cycles in 3 d. This work provides an insight into the synthesis of g‐C₃N₄‐based D‐π–A‐π–D systems with highly visible light response and long lifetime of intramolecular charge carriers for solar fuel production.     

Notch stress analyses of high‐frequency mechanical impact‐improved welds by using ρf = 1 mm and ρf = ρ + 1 mm approaches

This paper presents further assessments of the previously reported round‐robin fatigue data obtained from high‐frequency mechanical impact (HFMI)‐improved longitudinal welds. A detailed statistical analyses of geometry measurements of HFMI‐treated weld toe profiles are presented. The fatigue analyses based on notch stress as defined by the International Institute of Welding are performed using the finite element method. Notch stresses are assessed based on both the fictitious weld toe radius and the addition of measured actual notch radius to the fictitious radius. While no large differences are observed between the results of methods, the former one is found to be more practical and faster to implement from the end‐user point of view.     

Random Lasing in π‐Conjugated Films and Infiltrated Opals

The properties of random lasers in π‐conjugated polymer films and solutions infiltrated into opal photonic crystals are reviewed. We show that random lasing is a generic phenomenon that occurs in disordered gain media at an excitation intensity regime higher than that giving rise to amplified spontaneous emission. The emission radiation is coherent as demonstrated by photon statistics methods, and its spectrum contains many laser modes from which a typical cavity length can be obtained using Fourier transform spectroscopy. Since the random cavities are independent from each other, we show that laser emission in several colors is possible when mixing different dyes in the same random cavities. In addition, it is demonstrated that random lasing is formed in many disordered media with various scattering properties ranging from a regime of light prelocalization to that of weak scattering.     

Design of High‐Mobility Diketopyrrolopyrrole‐Based π‐Conjugated Copolymers for Organic Thin‐Film Transistors

Since the report of the first diketopyrrolopyrrole (DPP)‐based polymer semiconductor, such polymers have received considerable attention as a promising candidate for high‐performance polymer semiconductors in organic thin‐film transistors (OTFTs). This Progress Report summarizes the advances in the molecular design of high‐mobility DPP‐based polymers reported in the last few years, especially focusing on the molecular design of these polymers in respect of tuning the backbone and side chains, and discussing the influences of structural modification of the backbone and side chains on the properties and device performance of corresponding DPP‐based polymers. This provides insights for the development of new and high‐mobility polymer semiconductors.     

A ψ–ω finite element formulations for the Navier-Stokes equations

A new method of solving the two-dimensional Navier–Stokes equations by using the finite element method is proposed. The flow is represented by the stream function–vorticity formulation and the no-slip boundary conditions are explicitly introduced in the nonlinear equations. This formulation coupled with the Newton-Raphson method enables the study of stationary flows for high Reynolds number, without any convergence problem. A number of flow problems are analysed in order to demonstrate the efficiency of the present formulation.