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  1. Side chain engineering of non-planar zinc(ii) complexes of azadipyrromethene enables either very high hole mobility, high electron mobility or both as estimated by the space-charge limited current (SCLC) method in diodes.

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    Free, publicly-accessible full text available January 1, 2025
  2. Zinc(II) complexes of azadipyrromethenes are non-planar chromophores with strong absorption in the visible to NIR and are promising n-type materials for organic solar cells. To increase solubility and tune their properties, we incorporated hexyl or hexyloxy solubilizing groups either on the distal or proximal phenyls of bis[2,6-diphenylethynyl-1,3,7,9-tetraphenyl azadipyrromethene] zinc(II) (Zn(WS3)2). Crystal structures confirm the typical distorted tetrahedral geometry for these types of complexes and show that the solubilizing groups on the distal phenyls extend away from the conjugated core whereas groups on proximal phenyls interact with the other ligand. Differential scanning calorimetry measurement indicated that crystals of distal-substituted complexes have two endothermic peaks: solubilizing groups ‘melting’ and complex melting, whereas the proximal substituted complexes show one exothermic crystallization peak and one endothermic melting peak. Electrochemical and optical properties varied as expected for ADP-based complexes: the presence of electron rich groups at the proximal substitutions resulted in lower oxidation potentials, higher HOMO levels, red-shifted absorption and lower optical gap than distal substitutions, and the effect was greater for hexyloxy than hexyl. Upon thermal annealing, films of the hexyloxy-substituted complexes strongly aggregated and showed crystal features under a polarized microscope, indicating that hexyloxy groups drive ordered self-assembly, especially when placed on distal phenyls. The ability to guide solid-state self-assembly of these non-planar chromophores using solubilizing groups have the potential to improve their charge carrier mobility and performance in opto-electronic applications such as organic solar cells, and photodetectors. 
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  3. Abstract

    Electrospun biopolymer fibers are utilized in a wide variety of industries such as tissue engineering, sensors, drug delivery, membrane filtration, and protective membranes. The biopolymer chitosan, the partiallyN‐deacetylated derivative of chitin, which has been the focus of many studies, contains amine or hydroxyl functionalities that may be substituted with a number of chemistries such as carboxylate, benzene, or cyano groups. Modified chitosan solutions are often challenging to electrospin, as an entirely new set of solution and operating conditions must be developed for each modification. In this study, a facile post‐modification processing method for chitosan is introduced that circumvents the need to perform bulk modification prior to electrospinning, and therefore new spinning conditions. The chitosan mats were solution‐phase post‐processed by chemically functionalizing the mats with carboxylate, benzene and cyano groups. Scanning electron microscopy and Fourier‐transform infrared have been performed to determine fiber morphology retention and chemical interactions, respectively. Post‐modification retained the fibrous structure of the white‐colored, round and smooth mats with spectral changes indicating changes in the chitosan mat. Mean fiber diameters were 131 ± 75 nm (~31% smaller), 210 ± 81 nm (46% larger), and 85 ± 29 nm (~11% smaller) for carboxymethylchitosan, benzylidenechitosan, and cyanochitosan, respectively.

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