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Tetraphenylazadipyrromethenes (ADPs) are attractive near-infrared (NIR) dyes because of their simple synthesis and exceptional optical and electronic properties. The typical BF2 and less explored intramolecular BO coordination planarize the molecule, making them promising π-conjugated materials for organic electronic applications. However, their use has been mostly limited to vacuum-deposited devices. To improve the properties, we synthesized and characterized a series of ADP complexes and used density functional theory calculations to further explain the properties. Hexyloxy solubilizing groups increase the complexes’ solubility in organic solvents and enable film formation from solution. Phenylethynyls at the pyrrolic positions extend π conjugation, red-shift absorption and emission peaks, and increase the ionization potential (IP) and electron affinity. When the properties of complexes with hexyloxy and phenyethynyl substitutions are compared, the BO complex is more planar and has a smaller IP than the corresponding BF2 complex because of increased electron density on the proximal phenyls. The BO complex has an unusual combination of properties: a solution λmax of 781 nm, emission at 805 nm, a small Stokes shift, and a quantum yield of 6%. It forms transparent films with a low optical gap of 1.22 eV. This new complex is a promising candidate for transparent solar cells and NIR photodetectors.

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 partially N-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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