No abstract

The branching point of the side-chain of naphthalenediimide (NDI)-based conjugated polymers is systematically controlled by incorporating four different side-chains, i.e., 2-hexyloctyl (P(NDI1-T)), 3-hexylnonyl (P(NDI2-T)), 4-hexyldecyl (P(NDI3-T)), and 5-hexylundecyl (P(NDI4-T)). When the branching point is located farther away from the conjugated backbones, steric hindrance around the backbone is relaxed and the intermolecular interactions between the polymer chains become stronger, which promotes the formation of crystalline structures in thin film state. In particular, thermally annealed films of P(NDI3-T) and P(NDI4-T), which have branching points far away from the backbone, possess more-developed bimodal structure along both the face-on and edge-on orientations. Consequently, the field-effect electron mobilities of P(NDIm-T) polymers are monotonically increased from 0.03 cm 2 V −1 s −1 in P(NDI1-T) to 0.22 cm 2 V −1 s −1 in P(NDI4-T), accompanied by reduced activation energy and contact resistance of the thin films. In addition, when the series of P(NDIm-T) polymers is applied in all-polymer solar cells (all-PSCs) as electron acceptor, remarkably high-power conversion efficiency of 7.1% is achieved along with enhanced current density in P(NDI3-T)based all-PSCs, which is mainly attributed to red-shifted light absorption and enhanced electron-transporting ability.

Metal–organic frameworks are known to contain defects within their crystalline structures. Successful engineering of these defects can lead to modifications in material properties that can potentially improve the performance of many existing frameworks. Herein, we report the high-throughput computational screening of a large experimental metal–organic framework database to identify 13 frameworks that show significantly improved methane storage capacities with linker vacancy defects. The candidates are first identified by focusing on structures with methane-inaccessible pores blocked away from the main adsorption channels. Then, organic linkers of the candidate structures are judiciously replaced with appropriate modulators to emulate the presence of linker vacancies, resulting in the integration and utilization of the previously inaccessible pores. Grand canonical Monte Carlo simulations of defective candidate frameworks show significant enhancements in methane storage capacities, highlighting that rational defect engineering can be an effective method to significantly improve the performance of the existing metal–organic frameworks.

With growing focus on the use of carbon nanomaterials in chemical sensors, one-dimensional graphene nanoribbon (GNR) has become one of the most attractive channel materials, owing to its enhanced conductance fluctuation by quantum confinement effects and dense, abundant edge sites. Due to the narrow width of a basal plane with one-dimensional morphology, chemical modification of edge sites would greatly affect the electrical channel properties of a GNR. Here, we demonstrate for the first time that chemically functionalizing the edge sites with aminopropylsilane (APS) molecules can significantly enhance the sensing performance of the GNR sensor. The resulting APSfunctionalized GNR has a sensitivity ((ΔR/R b ) max ) of ∼30% at 0.125 ppm nitrogen dioxide (NO 2 ) and an ultrafast response time (∼6 s), which are, respectively, 7-and 15-fold enhancements compared to a pristine GNR sensor. This is the fastest and most sensitive gas-sensing performance of all GNR sensors reported. To demonstrate the superiority of the GNR-APS sensor, we compare its sensing performance with that of APS-functionalized carbon nanotube (CNT) and reduced graphene oxide (rGO) sensors prepared in identical synthesis conditions. Very interestingly, the GNR-APS sensor exhibited 30-and 93-fold enhanced sensitivity compared to the CNT-APS and rGO-APS sensors. This might be attributed to highly active edge sites with superior chemical reactivity, which are not present in CNT and rGO materials. Density functional theory clearly shows that the greatly enhanced gas response of GNR with edge functionalization can be attributed to the higher electron densities in the highest occupied molecular orbital levels of GNR-APS and incorporation of additional adsorption sites. This finding is the first demonstration of the importance of edge functionalization of GNR for chemical sensors.

Conductive metal–organic frameworks (cMOFs) are emerging materials for various applications due to their high surface area, high porosity, and electrical conductivity. However, it is still challenging to develop cMOFs having high surface reactivity and durability. Here, highly active and stable cMOF are presented via the confinement of bimetallic nanoparticles (BNPs) in the pores of a 2D cMOF, where the confinement is guided by dipolar‐interaction‐induced site‐specific nucleation. Heterogeneous metal precursors are bound to the pores of 2D cMOFs by dipolar interactions, and the subsequent reduction produces ultrasmall (≈1.54 nm) and well‐dispersed PtRu NPs confined in the pores of the cMOF. PtRu‐NP‐decorated cMOFs exhibit significantly enhanced chemiresistive NO2 sensing performances, owing to the bimetallic synergies of PtRu NPs and the high surface area and porosity of cMOF. The approach paves the way for the synthesis of highly active and conductive porous materials via bimetallic and/or multimetallic NP loading.