The effect of atomic substitution on the optoelectronic properties of a coplanar donor–acceptor (D–A) semiconducting polymer (SPs), prepared using cyclopentadithiophene (CDT) and 2,1,3‐benzothiadiazole (BT) moieties, is investigated. By substituting a carbon atom in the BT unit with CF or C–Cl, two random D–A SPs are prepared, and their optoelectronic properties are thoroughly investigated. Density functional theory calculations demonstrate that the fluorinated polymer has a slightly smaller dihedral angle (ϴ = 0.6°) than the pristine polymer (ϴ = 1.9°) in its lowest‐energy conformation, implying efficient charge transport through the coplanar backbone of the fluorinated polymer. However, the chlorinated polymer shows the lowest energy at a relatively larger dihedral angle (ϴ = 139°) due to the steric hindrance induced by bulky chlorine atoms in the backbone, thereby leading to thin‐film morphology, which is unfavorable for charge transport. Consequently, the fluorinated polymer yields the highest field‐effect mobility (μ) of 0.57 cm2 V−1 s−1, slightly higher than that of the pristine polymer (μ = 0.33 cm2 V−1 s−1), and the extended device lifetime of organic field‐effect transistors over 12 d without any encapsulation layers. The results of this study provide design guidelines for air‐stable D–A SPs.

Front Cover: In article number 2100709 by Byoung Hoon Lee and co‐workers, the effect of chlorine atom substitution on the optoelectronic properties of cyclopentadithiophene‐based donor–acceptor π‐conjugated polymers is investigated. The chlorine atom substitution leads to deteriorated optical and electrical properties of the polymer due to chain distortion as a consequence of steric hindrance adjacent to the chlorine atoms.

The determination of trypsin activity in human urine is important for evaluating pancreatic disease. We designed an effective fluorescence sensing strategy based on a self-assembled amphiphilic pyrene/protamine complex system that provides an amplified fluorescence response for highly sensitive and selective detection of trypsin. In aqueous solution, the functionalized pyrene formed fluorescent, π-extended aggregates inside micelles, which were effectively quenched by protamine (a trypsin substrate). However, this quenched fluorescence was very sensitively recovered by the trypsin’s enzymatic reaction, and this was attributed to a marked reduction in enhanced exciton migration caused by protamine in π-delocalized pyrene aggregates. The devised sensing platform was successfully utilized to selectively and sensitively detect trypsin at very low concentrations (0.03–0.5 μg mL–1) in non-pretreated human urine and to screen for trypsin inhibitors at concentrations of 0.1–5.0 μg mL–1.