Ammonia is not only a highly important gas for civilization but also contribute significantly for climate change and human health hazard. Highly sensitive ammonia sensor has been developed from a fluorescent zwitterionic spirocyclic Meisenheimer complex. Moreover, formation of this Meisenheimer complex can also be utilized for selective as well as naked eye instant detection of nitro aromatic explosive picric acid. The presence of a quaternary nitrogen atom directly attached to the spiro carbon is the unique feature of this Meisenheimer complex. This excellent photoluminescent (PL) Meisenheimer complex has two distinct stimuli responsive sites. One is sensitive towards acid while the other one is towards the base. These two positions can be modulated by adding one equivalent acid and one equivalent base to result two new products which are non fluorescent. One of these two non fluorescent species was found very exciting because of its UV/Vis transparency. Utilizing this concept we have fabricated an on-line sensor for measuring ammonia in dry or humid and condensing sewer air. The sensor was robust against ambient temperature and humidity variation. We have also developed an invisible ink from this Meisenheimer complex, with potential application for security purpose.

The Boc and N,N'-dicyclohexylurea capped γ-amino acid upon monobromination showed phosphorescence in the solid state. The compound exhibited different photoluminescence intensity and lifetimes in crystals obtained from ethyl acetate and methanol. X-ray crystallography revealed that the intermolecular C=O…Br halogen bond directs the heavy atom effect to produce the phosphorescence.

Different assembly and behaviour of homologous discotic tricarboxyamides containing b-alanine and gaminobutyric acid have been investigated. From UV/Vis and FT-IR spectroscopy the tricarboxyamides have similar self-assembly patterns. But, the tricarboxyamide 2 containing g-aminobutyric acid residues forms a gel in aromatic solvents after heating, cooling and ageing. However, the b-alanine analogue 1 failed to form a gel under the same conditions. From FE-SEM studies the tricarboxyamide 1 shows unbranched rod like morphology but the tricarboxyamide 2 exhibits an entangled fiber network. Finally, the X-ray crystallography reveals that both the tricarboxyamides 1 and 2 adopt 3-fold intermolecular Hbonded helical columnar structures. Detailed structural analysis shows that the individual helical columnar structures of tricarboxyamide 2 are themselves self-assembled through multiple hydrophobic interactions between side chains and thereby form a supramolecular network structure. However, the tricarboxyamide 1 columns are self-assembled into a supramolecular bundle-like structure. The result indicates that side chain interactions have a drastic effect on quaternary structure and function.

A supramolecular complex of syn-(methyl,methyl)bimane (1) and β-cyclodextrin demonstrates a sensitive (limit of detection = 0.60 nM) and selective fluorescence turn-off response in the presence of cobalt in aqueous media,...

Reported herein is the detection of iodine using a non‐covalent association complex formed between a β‐cyclodextrin host and a designer bimane ditriazole guest. This complex responds to the presence of iodine with a marked decrease in the observed fluorescence signal. A sub‐nanomolar detection limit of this system in the solution‐state was determined. Moreover, results using filter paper onto which the β‐cyclodextrin‐bimane complex was adsorbed show a noticeable advantage compared to the cyclodextrin‐free bimane. Thus, highly sensitive on‐paper colorimetric iodine detection was achieved.