Tunable Self‐Assembled Micro/Nanostructures of Carboxyl‐Functionalized Squarylium Cyanine for Ammonia Sensing

Abstract

Orderly molecular self‐assembly for tunable micro/nanostructures is an effective way to prepare novel functional materials with desired properties. Squarylium cyanine (SCy) dyes have received great attention in the fields of laser, imaging, and optoelectronic device. However, the detailed self‐assembly behavior of SCy has rarely been investigated. In the present work, two SCy derivatives, D1 and D2, respectively, bearing four and two carboxylic acid groups at different positions are prepared and used as a model system to investigate the molecular self‐assembly, morphology, and optical properties of SCy dyes. The hydrogen‐bonding interactions between the carboxylic acid groups in D1 and D2 are determined with X‐ray diffraction, 2D nuclear magnetic resonance, and Fourier transformation infrared spectroscopy. The two types of hydrogen bonds in D1 cooperating with inherent π–π stacking interaction result in tunable molecular aggregations, which further leads to the transformation between J‐aggregation and H‐aggregation of D1 in the solid state in response to ammonia gas. In all, this work provides a feasible and effective way to study the self‐assembled aggregates of SCy dyes at both molecular and supramolecular levels, and has developed a reversible sensor for ammonia gas detection.

A Cyanine Dye Encapsulated Porous Fibrous Mat for Naked‐Eye Ammonia Sensing

“…Dye D1 with four carboxylic acid groups (Scheme ) was synthesized according to our previous report . The carboxylic acid groups afford strong polarity, stable intermolecular hydrogen bonds, and potential reaction sites for alkaline reagents. The functionalized dye was encapsulated into PLA, and then the PLA‐Cy mat was fabricated by electrospinning (Figure a).…”

“…To support this hypothesis further, the micromorphology of D1 in the solid state was determined by SEM. Aggregated particles with sizes up to 300 nm are formed in the DMF solution of D1 (1×10 −5 m ) owing to hydrogen bonding between the carboxylic acid groups and π–π stacking between the backbones of D1 (Figure a) . PLA without the addition of the dye would form a filmlike morphology instead of the nanocapsule morphology (Figure b).…”

Kinetically Trapped Supramolecular Assembly of Perylene Dianhydride Derivative in Methanol: Optical Spectra, Morphology, and Mechanisms

“…This can be attributed to the disintegration of the H‐aggregates and the emergence of the fluorescent TP‐PDA monomers under acidic conditions. The absorption peak of the nanospheres was blueshifted compared with that of monomeric TP‐PDA, which indicates that the TP‐PDA molecules in H‐aggregates overlap with face‐to‐face stacking . The internal structure of self‐assembled nanostructures of TP‐PDA was also investigated by using X‐ray diffraction (XRD) analysis (Figure ).…”

Controlling Crystal Structures and Multiple Thermo‐ and Vapochromic Behaviors of Benzimidazole‐Based Squaraine Dyes by Molecular Design and Solvent Adjustment

“…In addition, Yin et al. were the first to demonstrate the influence of H‐bonding on the aggregation behavior and the related fluorescent properties of 1,3‐SQs by introducing different numbers of carboxylic acid groups . To the best of our knowledge, the detailed optical/fluorescent behaviors of SQs, in particular 1,2‐SQs, caused by morphology control have not been reported so far.…”