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A study of cofacially arrayed π-systems is of particular importance for the design of functional materials for efficient long-range intra-chain charge transfer through the bulk semiconducting materials in the layers of photovoltaic devices. The effect of π-stacking between a pair of aromatic rings has been mainly studied in the form of cyclophanes, where aromatic rings are forced into a sandwich-like geometry, which extensively deforms the aromatic rings from planarity. The synthetic difficulties associated with the preparation of cyclophane-like structures has prevented the synthesis of many examples of their multi-layered analogues. Moreover, the few available multi-layered cyclophanes are not readily amenable to the structural modification required for the construction of D–spacer–A triads needed to explore mechanisms of electron and energy transfer. In this review, we recount how a detailed experimental and computational analysis of 1,3-diarylalkanes led to the design of a new class of cofacially arrayed polyfluorenes that retain their π-stacked structure. Thus, efficient synthetic strategies have been established for the ready preparation of monodisperse polyfluorenes with up to six π-stacked fluorenes, which afford ready access to D–spacer–A triads by linking donor and acceptor groups to the polyfluorene spacers via single methylenes. Detailed ¹H NMR spectroscopy, X-ray crystallography, electrochemistry, and He(I) photoelectron spectroscopy of F2–F6 have confirmed the rigid cofacial stacking of multiple fluorenes in F2–F6, despite the presence of rotatable C–C bonds. These polyfluorenes (F2–F6) form stable cation radicals in which a single hole is delocalized amongst the stacked fluorenes, as judged by the presence of intense charge-resonance transition in their optical spectra. Interestingly, these studies also discern that delocalization of a single cationic charge could occur over multiple fluorene rings in F2–F6, while the exciton is likely localized only onto two fluorenes in F2–F6. Facile synthesis of the D–spacer–A triads allowed us to demonstrate that efficient triplet energy transfer can occur through π-stacked polyfluorenes; the mechanism of energy transfer crosses over from tunneling to hopping with increasing number of fluorenes in the polyfluorene spacer. We suggest that the development of rigidly held π-stacked polyfluorenes, described herein, with well-defined redox and optoelectronic properties provides an ideal scaffold for the study of electron and energy transfer in D-spacer-A triads, where the Fn spacers serve as models for cofacially stacked π-systems. Full article

There are many different fields in which wireless sensor networks (WSNs) can be used such as environmental monitoring, healthcare, military, and security. Due to the vulnerability of WSNs, reliability is a critical concern. Evaluation of a WSN’s reliability is essential during the design process and when evaluating WSNs’ performance. Current research uses the reliability block diagram (RBD) technique, based on component functioning or failure state, to evaluate reliability. In this study, a new methodology-based RBD, to calculate the energy reliability of various proposed chain models in WSNs, is presented. A new method called D-Chain is proposed, to form the chain starting from the nearest node to the base station (BS) and to choose the chain head based on the minimum distance D, and Q-Chain is proposed, to form the chain starting from the farthest node from the BS and select the head based on the maximum weight, Q. Each chain has three different arrangements: single chain/single-hop, multi-chain/single-hop, and multi-chain/multi-hop. Moreover, we applied dynamic leader nodes to all of the models mentioned. The simulation results indicate that the multi Q-Chain/single-hop has the best performance, while the single D-Chain has the least reliability in all situations. In the grid scenario, multi Q-Chain/single-hop achieved better average reliability, 11.12 times greater than multi D-Chain/single-hop. On the other hand, multi Q-Chain/single-hop achieved 6.38 times better average reliability than multi D-Chain/single-hop, in a random scenario. Full article