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Fluoroanthradithiophenes are well known organic semiconductors, where alkynyl substituents featuring silicon and germanium exhibit hole mobilities in excess of 5 cm 2 V −1 s −1 . A key feature to achieve these performance levels is the 2-dimensional brickwork packing of triethylsilyl and triethylgermyl side chains, which direct solid-state packing, increase molecular stability, and increase solution processability for cheap and large scale fabrication. We have recently reported side chains utilising carbon in place of the other group 14 atoms, resulting in less favourable 1-dimensional molecular packing. Here we present the synthesis of new derivatives which adopt 2-D brickwork packing without the use of silicon or germanium to determine substituent effects on charge carrier mobility. 

A carbon side-chain analogue to the high-performance organic semiconductor triethylsilylethynyl difluoroanthradithiophene has been synthesised and characterized. Atomic substitution of carbon for silicon results in subtle changes to opto-electronic properties, which are rationalised by density functional theory and balance of electron donating and withdrawing effects. Larger differences are observed in photostability and solid-state packing of the new material in comparison to known silicon and germanium derivatives. Comparison of the group 14 elements teaches us about the newly synthesised system, but also how the silylethynyl substituents used for the last two decades contribute to successful employment of functionalised polycyclic aromatic hydrocarbons as organic semiconductors. 

Photoinduced electron transfer into mesoporous oxide substrates is well-known to occur efficiently for both singlet and triplet excited states in conventional metal-to-ligand charge transfer (MLCT) dyes. However, in all-organic dyes that have the potential for producing two triplet states from one absorbed photon, called singlet fission dyes, the dynamics of electron injection from singlet vs. triplet excited states has not been elucidated. Using applied bias transient absorption spectroscopy with an anthradithiophene-based chromophore ( ADT-COOH ) adsorbed to mesoporous indium tin oxide ( nanoITO ), we modulate the driving force and observe changes in electron injection dynamics. ADT-COOH is known to undergo fast triplet pair formation in solid-state films. We find that the electronic coupling at the interface is roughly one order of magnitude weaker for triplet vs. singlet electron injection, which is potentially related to the highly localized nature of triplets without significant charge-transfer character. Through the use of applied bias on nanoITO : ADT-COOH films, we map the electron injection rate constant dependence on driving force, finding negligible injection from triplets at zero bias due to competing recombination channels. However, at driving forces greater than −0.6 eV, electron injection from the triplet accelerates and clearly produces a trend with increased applied bias that matches predictions from Marcus theory with a metallic acceptor. 

Dehydroannulenes are alkyne‐rich macrocycles possessing rigid, planar, π‐conjugated backbones. Octadehydro[12]annulenes in particular are formally antiaromatic, and have been shown to possess stable reduced states with exploitable LUMO energies. However, very few examples of this type of annulene have been structurally characterized, and there is little information on the stability of these antiaromatic molecules in solution or in the solid state. We have synthesized a range of substituted octadehydro[12]annulenes, and characterized their optical and redox properties. Contrary to prior reports, dehydro[12]annulenes with overlapping π‐surfaces are reasonably stable both in solution and thin films, suggesting potential use in practical applications.

 

Organic mixed ionic and electronic conductors are of significant interest for bioelectronic applications. Here, three different isoindigoid building blocks are used to obtain polymeric mixed conductors with vastly different structural and electronic properties which can be further fine‐tuned through the choice of comonomer unit. This work shows how careful design of the isoindigoid scaffold can afford highly planar polymer structures with high degrees of electronic delocalization, while subtle structural modifications can control the dominant charge carrier (hole or electron) when probed in organic electrochemical transistors. A combination of experimental and computational techniques is employed to probe electrochemical, structural, and mixed ionic and electronic properties of the polymer series which in turn allows the derivation of important structure–property relations for this promising class of materials in the context of organic bioelectronics. Ultimately, these findings are used to outline robust molecular‐design strategies for isoindigo‐based mixed conductors that can support efficient p‐type, n‐type, and ambipolar transistor operation in an aqueous environment.

 

In order to understand how additives influence the structure and electrical properties of active layers in thin‐film devices, a compositionally identical but structurally different guest–host system based on thesynandantiisomers of triethylsilylethynyl anthradithiophene (TES ADT) is systematically explored. The mobility of organic thin‐film transistors (OTFTs) comprisingantiTES ADT drops with the addition of only 0.01% of thesynisomer and is pinned at the mobility of OTFTs having puresynisomer after the addition of only 10% of the isomer. As thesynisomer fraction increases, intermolecular repulsion increases, resulting in a decrease in the unit‐cell density and concomitant disordering of the charge‐transport pathway. This molecular disorder leads to an increase in charge trapping, causing the mobility of OTFTs to drop with increasingsyn‐isomer concentration. Since charge transport is sensitive to even minute fractions of molecular disorder, this work emphasizes the importance of prioritizing structural compatibility when choosing material pairs for guest–host systems.